Thermodynamics and the Intrinsic Stability of Lead Halide Perovskites CH3NH3PbX3Click to copy article linkArticle link copied!
- Andrea Ciccioli*Andrea Ciccioli*E-mail: [email protected]Department of Chemistry, Sapienza − University of Rome, Piazzale Aldo Moro 5, 00185 Rome, ItalyMore by Andrea Ciccioli
- Alessandro LatiniAlessandro LatiniDepartment of Chemistry, Sapienza − University of Rome, Piazzale Aldo Moro 5, 00185 Rome, ItalyMore by Alessandro Latini
Abstract
The role of thermodynamics in assessing the intrinsic instability of the CH3NH3PbX3 perovskites (X = Cl,Br,I) is outlined on the basis of the available experimental information. Possible decomposition/degradation pathways driven by the inherent instability of the material are considered. The decomposition to precursors CH3NH3X(s) and PbX2(s) is first analyzed, pointing out the importance of both the enthalpic and the entropic factor, the latter playing a stabilizing role making the stability higher than often asserted. For CH3NH3PbI3, the disagreement between the available calorimetric results makes the stability prediction uncertain. Subsequently, the gas-releasing decomposition paths are discussed, with emphasis on the discrepant results presently available, probably reflecting the predominance of thermodynamic or kinetic control. The competition between the formation of NH3(g) + CH3X(g), CH3NH2(g) + HX(g) or CH3NH3X(g) is analyzed, in comparison with the thermal decomposition of methylammonium halides. In view of the scarce and inconclusive thermodynamic studies to-date available, the need for further experimental data is emphasized.
It is no exaggeration to say that the largest part of the current research efforts on lead halide-based and similar perovskite materials is directed toward the search for higher stability needed in photovoltaic applications. In the last five years, many authors expressed the concern that the low stability under the action of a number of external agents, including other device components, could be the main Achilles’ heel of this class of light harvester materials, very attractive in other respects, whose prototype is the well-known methylammonium lead iodide, CH3NH3PbI3. (1−6) As a consequence, a wealth of strategies were put in place to improve the material and device stability, based on chemical modifications (7−9) protection layers, (10) and encapsulation. (11)
Interaction with water/moisture has been soon identified as a major drawback. (12) Other external agents which many researchers focused on are oxygen and UV/visible radiation. (13) The study of these degradation processes was typically performed by following the change of properties/performances of the material/device, while the interaction takes place or ex post. To elucidate the progress and mechanism of degradation, a “microscopic” approach is most often applied, based on techniques such as XRD, UV–vis and NIR spectroscopy, fluorescence, microscopy, XPS, etc. (14−17) Theoretical calculations may be of help in identifying mechanistic details. (18) The effect of temperature on the perovskite stability was usually studied in conjunction with that of such chemical and physical agents. Incidentally, it should be mentioned that in some cases the diagnostic means used to study degradation (e.g., X-ray irradiation, electron currents) can themselves play a role in degradation phenomena. (19,20)
Comparatively little work has been carried out on the intrinsic (in)stability of these materials in itself, both in vacuo and under inert atmosphere, as a function of temperature. (21−24) In particular, very few studies are available based on a macroscopic thermodynamic approach. (25−27) Moreover, the available experimental and computational results are often discrepant. The goal of this Perspective is to discuss the issue of the intrinsic stability of CH3NH3PbX3 materials from a thermodynamic point of view in light of the information currently available, pointing out the persistent uncertainties and inconsistencies, which make urgent further experimental efforts. Special focus is done on the decomposition processes leading to the release of gaseous products.
Overall, we would like to emphasize in this paper the contribution that classic macroscopic thermodynamics can (or cannot) provide to the stability issues raised from the application of these materials to energy conversion technologies. It is important to underline that the thermodynamic characterization of a material as such is a crucial prerequisite to undertake reliable thermodynamic predictions and simulations of its behavior in various chemical and physical environments. Furthermore, ascertaining the intrinsic (in)stability of a material is essential for practical applications, because if the material is found to be inherently unstable, any protection strategy may be undermined. Regrettably, from an analysis of the literature trends, one has the clear impression that experimental thermodynamic studies cannot keep pace with the wealth of new material modifications that are proposed at an ever-increasing rate to overcome instability issues.
In the broadest sense, investigating the thermodynamic stability of a material means to wonder if, under a given set of external conditions, the material will remain unchanged or it will undergo some kind of chemical/physical transformation, ultimately driven by entropy production. The number of possible transformation pathways of the system is, in general, high and difficult to predict. In a stricter and more practical sense, one usually evaluates the thermodynamic driving force or affinity, , for one or a few among the many possible decomposition/degradation reactions, where νi and μi are, respectively, the stoichiometric coefficients (taken as negative for the left-hand reactants of the chemical/physical degradation process) and the chemical potentials of all the species involved. If the affinity is found to be negative under the conditions of interest (for example, for given pressure and temperature), the selected decomposition/degradation path is thermodynamically favored. Otherwise, the material is stable as far as that path is considered, and indeed its formation from right-hand products is thermodynamically favored. In this approach, the final products of the process are to be known or an hypothesis has to be done. In the case of CH3NH3PbX3 compounds, the decomposition to the synthesis precursors was most often considered in theoretical evaluations (Figure 1):
Figure 1
Figure 1. Enthalpy and entropy level scheme for possible formation/decomposition processes of CH3NH3PbX3 perovskites. Decomposition to precursors can be both endothermic and exothermic. The minor process leading to the formation of CH3NH3X(g) (see Figure 3) is not shown. Enthalpy levels are not to scale.
Although considering this reaction is probably the most natural choice in assessing the formability of CH3NH3PbX3 compounds, it should be noted that, while PbI2(s) was much often reported as the main decomposition product under various conditions, apparently no experimental study reported the CH3NH3X solids among the observed products.
A huge number of theoretical calculations were performed to evaluate the energy/enthalpy change of the above reaction by the DFT approach. However, the results are significantly dependent on the chosen functional, the best performance being usually obtained with the PBEsol one, with the additional inclusion of spin–orbit contributions. (28,29) A fairly rich selection of results is reported in Table 1. As for experiments, regrettably, only two direct determinations of ΔrH°(1) are available in the literature, both obtained by solution calorimetry at T = 298 K, using DMSO (25) or aqueous HCl (26) as a solvent. Note that, although at 298 K CH3NH3PbI3 is stable in the tetragonal form, measurements of ref (25) were performed on the (metastable) cubic high temperature phase. A third experimental value for reaction 1 can be derived from the vapor pressure measurements carried out by effusion-based techniques on the equilibrium (reaction 8) discussed in the next section. (27)
theory (DFT) | thermodynamic experiments | |||||||
---|---|---|---|---|---|---|---|---|
X | ΔEb | ref. | ΔH298K° | method and ref | S298K°c | ΔS298K°d | ΔG298K° | stable with respect to precursors at 298 K, 1 bare |
Cl (cubic) | 12 | (30) | 9.03 ± 1.68 | solution calorim. in HCl (26) | 313.37 | −38.77 | 11.6 | YES |
68 | (31) | 4.45 ± 0.34 | solution calorim. in DMSO (25) | 16.0 | YES | |||
0.39–3.9 | (32) | 2.8 ± 7.8 | vapor pressure (KEML, KEMS) (27) | 11.6 | YES | |||
Br (cubic) | 12 | (30) | –6.69 ± 1.41 | solution calorim. in HCl (26) | 349.29 | −39.9 | 5.2 | YES |
24 | (31) | 6.78 ± 0.97 | solution calorim. in DMSO (25) | 18.7 | YES | |||
1.4–4.1 | (32) | 3.3 ± 8.7 | vapor pressure (KEML, KEMS) (27) | 15.2 | YES | |||
I (tetragonal) | 2.7–3.4 | (22) | solution calorim. in HCl (26) | 374.15 | –39.6 | –22.7 | NO | |
9.6 | (33) | −34.50 ± 1.01 | ||||||
2.2 | (29) | |||||||
4.8 | (34) | |||||||
–8.7 | (35) | −1.913 ± 1.12f | solution calorim. in DMSO (25) | 9.9 | YES | |||
5.8 | (36) | |||||||
9.6 | (31) | |||||||
–5.8/–6.1 | (32) | |||||||
0.39 | (37) | 0.39 ± 9.7 | vapor pressure (KEML, KEMS) (27) | 11.4 | YES | |||
2.4 | (38) | |||||||
3.9 | (39) | |||||||
I (cubic)g | –4.8 | (28) | –4.493 ± 1.12 | solution calorim. in DMSO (25) | 383.85c | –49.3 | 10.2 | YES |
–1.9 | (30) | |||||||
26 | (40) | |||||||
–11/–12 | (32) |
Energies and enthalpies are in kJ/mol, entropies in J/K mol.
For an accurate comparison of the theoretical ΔEs with the thermochemical ΔH298K°, small effects due to zero-point energy, finite temperature and standard pressure should be considered. The corrections due to the heat content difference (H298 K–H0K) and the P°ΔV terms are of the order of few kJ/mol and J/mol, respectively.
Absolute entropies of CH3NH3PbX3 are from ref (41). The value for the high temperature cubic phase of CH3NH3PbI3 was estimated by adding the tetragonal-cubic transition entropy (9.7 J/K mol, measured at 330 K41) to S298K° of the tetragonal phase.
Entropies of CH3NH3X(s) and PbX2(s) are from the compilation of ref (25). except for CH3NH3Br, whose S298K°was estimated by us as 148.2 J/K mol by a volume-based-thermodynamics approach. (42)
Based on the sign of ΔG298K°, which for reactions (1) corresponds to the driving force ΔrG at 298 K and 1 bar.
Evaluated by adding the t-c transition enthalpy (2.58 kJ/mol, measured at 330 K41) to the ΔH298K° value measured for the cubic phase. (25)
The tetragonal to cubic transition enthalpy of CH3NH3PbI3 is 2.58 kJ/mol, measured at 330 K. (41)
A compilation of all the results is reported in Table 1. Somehow surprisingly, the two calorimetric determinations are not in agreement, showing a discrepancy definitely outside the claimed experimental uncertainties. For CH3NH3PbI3, in particular, the very negative value of ΔrH°(1) found in ref (26), which led those authors to claim the instability of the compound, was not confirmed by the subsequent measurements in DMSO, (25) making difficult any conclusive prediction on the spontaneous direction of reaction (1) at room temperature for X = I. Also the stability trend from Cl to Br to I is not in agreement between the two studies (Figure 2). The values of ref (26) suggest the Cl > Br > I stability trend, which is consistent with the Goldschmidt’s tolerance factor traditionally used to rationalize the stability of perovskite phases. However, tensimetric results (27) agree well with the Ivanov’s data, (25) which is a nice occurrence in view of the completely different experimental approach used.
Figure 2
Figure 2. Stability order of CH3NH3PbX3 for X = Cl,Br,I with respect to different processes.
Since reaction 1 involves pure solid phases, ΔrG° is practically coincident with the thermodynamic driving force for decomposition, ΔrG, provided that pressure is not too high. The last column of Table 1 indicates the stability of perovskite compounds with respect to precursors of reaction 1. On the basis of the available information, it is concluded that for X = Cl and Br decomposition is thermodynamically disfavored at 298 K, whereas for X = I the results are conflicting: depending on the selected enthalpy change, the negative entropic term can compensate it or not. On the basis of the agreement with tensimetric values, it seems reasonable to recommend provisionally the calorimetric results of Ivanov et al., (25) which provide the following expressions for ΔrG° of the decomposition reaction 1:
As mentioned, ascertaining the stability of a material referring to only one or several processes is not a conclusive proof of its absolute intrinsic stability. For example, in order to identify the most favored among a number of possible decomposition pathways of CH3NH3PbI3, a convex hull approach was used, leading to select the decomposition to NH4I + PbI2 + CH2 as the most stable path. (43) In this connection, it is interesting to note that the cleavage of the C–N bond with formation of hydrocarbon fragments −CH2– was recently observed in in situ-deposited CH3NH3PbI3 films by near ambient pressure XPS. (44)
Another process that is sometimes taken as representative of the intrinsic stability of a material is the opposite of the formation from elements, Pb + 1.5 X2 + 3 H2 + 0.5 N2 + C = CH3NH3PbX3, with all species in their reference phase (at the temperature of interest) and in the standard state (see Figure 1). (45) Consistent with eqs 2–4, the following expressions can be derived for ΔfG° of the CH3NH3PbX3 compounds, valid for the room temperature phases in a reasonably large temperature range:
These equations indicate that ΔfG° is strongly negative at temperatures close to room temperature and show the expected trend of stability with respect to elements, Cl > Br > I (Figure 2). Equations 5–7 can be combined with the corresponding expressions for other substances (H2O, PbO, PbCO3, HI, CH3NH2, etc.) to estimate the standard Gibbs energy change of chemical reactions potentially involved in the intrinsic or extrinsic (e.g., due to water or oxygen) degradation of the materials as well in synthesis and annealing processes. Note that for several important reactions (for example, those forming perovskite hydrate phases such as (CH3NH3)4PbI6·2H2O under exposure to moisture) ΔrG° cannot be evaluated owing to the lack of relevant thermodynamic data.
In view of the above discussion, the decomposition processes (1) should not be a worrisome decomposition path as far as methylammonium lead chloride and bromide perovskites are concerned, whereas the discrepancy between calorimetric data makes a conclusive assessment for iodide difficult. However, other decomposition channels could be at work under operative conditions. In particular, gas-releasing decomposition processes are of crucial importance for investigating the stability of CH3NH3PbX3 and similar materials. Grazing-incidence wide-angle X-ray diffraction measurements have shown recently (46) that the dramatic heat-induced performance decrease of encapsulated perovskite-based devices is due to surface modifications related to the intercalation of thermally decomposed methylammonium fragments into PbI2 planes. Since encapsulation is expected to prevent interaction with external agents, this is a clear evidence of intrinsically driven degradation related to the loss of volatile fragments, as already suggested in previous papers. (22,24) Furthermore, the type of gas that these materials tend to lose under heating may be of interest for real devices because gaseous products could interact with the sealing materials and with the other components of the cell. Finally, gas-phase releasing degradation is very important under conditions where the system is allowed to vaporize, such as postsynthesis annealing (47) and synthesis by vapor deposition techniques. (48) In spite of this, the direct experimental study of the released gaseous species has been the subject of relatively few studies that, unfortunately, presented problematic results. (27,49,50)
In this connection, the following gas-releasing processes are worth considering:
In all three cases, solid lead dihalide is formed, as invariably observed by means of solid state techniques, (27) and the CH3NH3X portion of the perovskite phase is lost, either as undissociated methylammonium halide or in the form of smaller molecules. In principle, gas-phase dissociation can occur by formation of HX or CH3X, depending on whether the methyl group or the proton associates with the halide ion. Theoretical analyses indicate as an energetically favored path to this kind of degradation the creation of HI vacancies and the subsequent combination of the amine fragment with Pb atoms, which disintegrates the inorganic framework. (51)
That the heat-induced degradation of CH3NH3PbI3 perovskites proceeds through mass loss has been shown by a number of thermogravimetric (TGA) measurements and has been also inferred by solid state techniques, for example by measuring the evolution of I/Pb and N/Pb ratios by photoelectron spectroscopy. (20)
Most investigations of the degradation of CH3NH3PbX3 to volatile species were carried out by classic TGA, where the mass loss rate is recorded as a function of temperature, usually under an inert dynamic atmosphere.
To the best of our knowledge, the first reports on the direct detection of the gas phase released by the CH3NH3PbX3 perovskites appeared in 2016, (27,49,54) although FTIR spectroscopy experiments were previously reported for the vaporization of dimethylformamide-CH3NH3PbClxI3–x solutions. (56)
Extensive vaporization experiments were first reported based on the classic Knudsen Effusion Mass Loss (KEML) and Knudsen Effusion Mass Spectrometry (KEMS) techniques. (27) KEMS measurements were carried out on all three CH3NH3PbX3 compounds in the overall temperature range 76–144 °C, much lower than decomposition temperatures found in TGA measurements. Mass spectra showed the large dominance of peaks attributable to HX(g) and CH3NH2(g), providing strong evidence of the occurrence of reaction 8 previously proposed in ref (54) based on Temperature-Programmed Desorption experiments. Weakest peaks corresponding to undissociated CH3NH3X(g) were also detected (it should be pointed out that electron impact mass spectrometry could cause the undissociated CH3NH3X(g) species to break into smaller fragment ions.). The thermodynamic analysis of partial pressure data allowed decomposition enthalpies to be derived for reaction 8 and, thereafter, formation enthalpies of CH3NH3PbX3 perovskites to also be evaluated. The latter were subsequently found to agree well with calorimetric results (see Table 1). (25,50) Shortly after, another study (49) was published where a very different behavior was observed by TGA-Mass Spectrometry experiments for CH3NH3PbI3 and for its precursor halide, CH3NH3I, which were found to release only NH3(g) and CH3I(g). Although the largest part of TGA-MS experiments were carried out at much higher temperatures (300–420 °C) than Knudsen measurements, authors obtained some indication that the same process would also take place at temperatures as low as 80 °C, close to those of interest for photovoltaic applications. Interestingly, the findings of ref (49) confirmed in part those previously obtained by FTIR. (56) FTIR spectra of the gas phase recorded at 265 °C indicated the decomposition of solid CH3NH3I to NH3(g) and CH3I(g), in contrast with CH3NH3Cl and CH3NH3PbCl3, which was observed to release HCl(g) and CH3NH2(g).
In order to shed some light on this scanty and discrepant experimental information, a thermodynamic analysis is useful.
In principle, reactions 8–10 may occur simultaneously, giving a three-phase monovariant equilibrium with seven components, two of them thermodynamically independent. While the absolute values of the partial pressures depend on the properties of the two condensed phases, the thermodynamic competition between the three reactions is basically due to the different stability of the gaseous species.
Using relations 5–7 for the Gibbs energy of formation of the perovskite phases and the corresponding well-established expressions for the products of reactions 8 and 9, the results reported in Table 2 are derived for the corresponding standard Gibbs energy changes. Data in Table 2 indicate that, at variance with the trend of formation enthalpies, the bromide perovskite is the most stable with respect to vaporization (Figure 2) for both processes 8 and 9. However, the stability trend is Br > I > Cl and Br > Cl > I, respectively, for the two processes. Note that only in the case of reaction 8 is the stability order in agreement with TGA experiments (see above). For the sake of comparison, in the same table, the ΔrG°’s are also reported for the corresponding decomposition reactions of methylammonium halides, CH3NH3X. It is interesting to note that ΔrG° values for the latter are lower (i.e., the decomposition pressures are higher at a given temperature) than those of the corresponding perovskites. A large part of this effect is due to the higher entropy changes for the decomposition of CH3NH3X compounds.
X | CH3NH3PbX3(s) = PbX2(s) + HX(g) + CH3NH2(g) (8) | CH3NH3PbX3(s) = PbX2(s) + CH3X(g) + NH3(g) (9) |
---|---|---|
Cl | 187.9 – 252.3 × 10–3T | 174.9– 249.6 × 10–3T |
Br | 206.9 – 253.3 × 10–3T | 183.3 – 250.3 × 10–3T |
Ib | 200.2 – 250.1 × 10–3T | 164.7 – 247.2 × 10–3T |
CH3NH3X(s) = HX(g) + CH3NH2(g) | CH3NH3X(s) = CH3X(g) + NH3(g) | |
---|---|---|
Cl | 183.5 – 291.1 × 10–3T | 170.5 – 288.3 × 10–3T |
Br | 200.1 – 293.3 × 10–3T | 176.6 – 290.3 × 10–3T |
I | 204.7 – 289.7 × 10–3T | 169.2 – 286.8 × 10–3T |
These expressions can be applied in a reasonably large temperature range near to 298 K.
Cubic phase of CH3NH3PbI3.
A similar analysis for process 10 is made difficult by the lack of thermodynamic data for the species CH3NH3X(g), which is not surprising if we consider that, even for the simpler ammonium halide species, NH4X(g), experimental data are more uncertain than one might believe. For example, the dissociation degree of NH4Cl(g) to NH3(g) and HCl(g) has been the subject of a longstanding debate, with experimental results ranging from complete to very limited dissociation and theoretical studies claiming for a fair stability of the undissociated hydrogen-bond linked species. (57) Although the CH3NH2 + HCl potential energy surface has been the subject of a number of theoretical studies aimed at clarifying the mechanism of the methyl exchange in solution phase (the so-called Menshutkin SN2 reaction, CH3Cl + NH3 = CH3NH3+Cl–), apparently a stable structure for the CH3NH3Cl complex in the gas phase was reported only recently by Patterson (58) based on DFT calculations. In order to evaluate the relative importance of reaction 10 for the iodide perovskite under thermodynamic conditions, similar calculations were done for the CH3NH3I(g) species, (59) that allowed us to derive an approximate estimate of ΔrG°(10) as
Figure 3
Overall, from this analysis the conclusion can be drawn that (i) process 9 has a much larger thermodynamic driving force, but (ii) under effusion conditions, which, in principle, should allow an approach toward thermodynamic equilibrium, the occurrence of this process is kinetically hindered, and the measured pressures suggest that process 8 takes place instead. The kinetic limitation of reactions 9 seems quite plausible because the breaking of a strong C–N bond (330 kJ/mol at 298 K) is required, instead of the hydrogen-bond breaking involved in process 8. This view is supported by DFT calculations, (49) which predict a remarkable activation barrier for reaction 9, and by the comparison with the thermal decomposition behavior of simple alkylammonium halides (see below). It should be noted that the very good agreement between calculated and experimental data indicates that, as far as process 8 is concerned, thermodynamic equilibrium is fully attained under Knudsen conditions, giving confidence in the thermodynamic properties derived from tensimetric measurements, provided that data are analyzed on the basis of the proper reaction.
In view of the above analysis, the aforementioned experimental results on the decomposition of CH3NH3PbX3 (especially in regard to CH3NH3PbI3) are somehow puzzling. Apparently, measurements under Knudsen conditions, which are supposed to favor the attainment of thermodynamic equilibrium, gave evidence for the occurrence of the thermodynamically disfavored process 8, whereas “open-pan” TGA-MS and IR experiments provided evidence for the occurrence of the thermodynamic pathway. Since the latter experiments were mostly performed in a much higher temperature range where kinetic hindrance might be overcome, the question arises whether different temperatures alone can account for the experimental findings or other effects are to be invoked, such as vacuum versus dynamic inert atmosphere, heating scan versus thermal equilibration, presence of a heated transfer line, etc.
More recent KEMS experiments (50) where the competition between processes 8 and 9 was studied by measuring the p(HI)/p(CH3I) ratio under different conditions, provided some additional information. The competition between the two processes is basically driven by the following homogeneous pressure-independent gaseous equilibrium: (50)
In view of the small entropy change of reaction 12, the partial pressure ratio 13 is ruled by the enthalpic factor. Since ammonia is much more thermally stable than methylamine (ΔfH298° = −45.94 and −22.5 kJ/mol, respectively), at the temperatures of interest equilibrium 12 is shifted toward the right, regardless of the nature of X. Furthermore, since HI is thermally unstable (ΔfH298° = 26.5 kJ/mol) compared to CH3I (ΔfH298° = 14.4 kJ/mol), the decomposition channel 8 is especially disfavored for iodide in comparison with chloride (ΔfH298° = −92.3 and −81.9 kJ/mol for HCl and CH3Cl, respectively), whereas the thermal stabilities of CH3Br and HBr are practically equal (ΔfH298° = −36.3 and −36.4 kJ/mol). Being exothermal, reaction 12 tends to shift to left at higher temperatures, although right-hand products remain strongly favored at any temperature of interest. In Figure 4, the p(HI)/p(CH3I) pressure ratio calculated by eq 13 is reported, along with the corresponding ratios measured by KEMS in a higher temperature range compared to ref (27), using two different effusion caps. (50) The red line refers to experiment carried out with an ordinary effusion hole (1 mm diameter, negligible thickness), the blue one was derived using a sort of “chimney” orifice, with 0.5 mm in diameter and a 6.5 mm long channel making the effusion rate lower (see the cap pictures in Figure 4). The higher impedance to effusion flow is expected to favor approaching the heterogeneous equilibrium. Indeed, Figure 4 clearly shows that (i) higher temperatures do favor the formation of CH3I (g) versus HI(g), contrarily to thermodynamic predictions (black line with negative slope in Figure 4), and (ii) high impedance effusion conditions have the same effect, decreasing the HI/CH3I ratio by more than 1 order of magnitude. A schematic picture of these findings is reported in Figure 5. Nevertheless, under all the explored conditions, process 8 remains the dominant decomposition pathway. Therefore, according to KEMS results, even at temperature as high as 250 °C, process 9 cannot come out by the extent predicted by equilibrium thermodynamics.
Figure 4
Figure 5
In an attempt to rationalize the observed decomposition behavior of CH3NH3PbX3 perovskites, a possible benchmark is given by the thermal decomposition of simple mono- di-, tri-, and tetralkylammonium halides, which have been the subject of quite a high number of studies. (61−63) On the basis of TGA experiments, Błażejowski and co-workers concluded that compounds of general formula RpNH4–pX decompose under heating according to the following processes: (62)
In other words, mono-, di- and trialkyl ammonium halides decompose, releasing the corresponding amine and hydrogen halide rather than by the alternative process releasing the alkyl halide and the less substituted amine:
As far as thermodynamic equilibrium is concerned, the above-reported discussion on the competition between processes 8 and 9 could be extended to processes 14 and 16. Indeed, the pressure ratio (process 12) in equilibrium with the CH3NH3PbX3 + PbX2 mixture is the same as that in equilibrium with the methylammonium halide solids CH3NH3X, and it is ruled by the relative stability of NH3(g) versus CH3NH2(g) and HX(g) versus CH3X(g), which would strongly favor process 16 (see above). Other cases can be more complex, since the relative stability of HX(g) and RX(g) depends markedly on X and that of RpNH3–p(g) versus Rp–1NH4–p(g) for p = 2,3 is not obvious.
The kinetic hindrance of the C–N bond-breaking process involved in decomposition reactions 15 and 16 is supported by the fact that quaternary amines, where process 14 cannot take place, are observed to decompose at much higher temperatures than less substituted compounds. (63) Furthermore, the enthalpy changes of the thermal decomposition of tetralkylammonium halides as measured by TGA have been found to be much higher than those measured by DSC (for instance, 319.7 kJ/mol versus 186.7 kJ/mol for (CH3)4NI (63)), which correspond to the actual energy required to convert the solid into gaseous products (i.e., the thermodynamic decomposition enthalpy). In TGA measurements, where the enthalpy change is obtained by the temperature dependence of the mass loss rate, the activation barrier is instead measured. DFT calculations fully support this view. For example, an activation energy of 239 kJ/mol was calculated recently (64) for the thermodynamically favored decomposition of dioctylammonium chloride to dioctylamine +1-chlorooctane, whereas no activation barrier is found for the alternative process leading to trioctylammonium chloride and HCl. While the outlined frame of the thermal behavior of alkylammonium halide seems fairly well-established, nonetheless the direct experimental evidence of process 14 for mono-, di-, and trisubstituted compounds seems scarce, and indeed recent perovskite-related experiments seem to call it into question. (49,56)
In conclusion, the intrinsic stability of CH3NH3PbX3 perovskites can be analyzed in the light of a classical thermodynamic analysis relying on the limited experimental information available to date. Decomposition reactions to solid precursors PbX2(s) and CH3NH3X(s) are shown to be thermodynamically disfavored for X = Cl, Br, in great part because of the large negative decomposition entropies. For X = I, the serious discrepancy between the calorimetric determinations does not allow one to draw definitive conclusions on the thermodynamic driving force of this decomposition pathway, although the entropic contribution certainly also plays a large stabilizing role in this case. Decomposition reactions are most likely to occur by the release of gaseous products, a process that, according to recent experimental findings, may play an important role even in encapsulated devices. However, the identification of the molecular species lost by the perovskite structure is still uncertain, and the limited experimental information is not conclusive. Decomposition to NH3(g) and CH3X(g) is largely favored from a thermodynamic point of view, but it seems to suffer from a severe kinetic limitation related to the breaking of the strong C–N bond in the organic cation, as previously observed in the thermal decomposition of alkylammonium halides. Indeed, TGA-MS measurements support the occurrence of this decomposition channel at high temperature for X = I. However, effusion experiments indicate, in spite of thermodynamic driving forces, the release of HX(g) and CH3NH2(g), rather than NH3(g) and CH3X(g), at temperatures much lower than the decomposition temperatures detected by TGA experiments. The thermodynamic pathway becomes more important at higher temperature and under closer-to-equilibrium effusion conditions. The release of undissociated CH3NH3X(g) molecules seems thermodynamically disfavored, although accurate thermodynamic data for these species are lacking. While thermodynamics prove to be very useful in rationalizing the degradation behavior of perovskite materials and corresponding precursors, careful attention has to be paid to kinetic effects. However, the scarcity and the uncertainty of the experimental data currently available is a serious limit to thermodynamic predictions, which would greatly benefit from increased research efforts aimed at determining accurate thermodynamic information by independent techniques under various conditions. It is desirable that, in the next years, chemical thermodynamics research will give a greater contribution to assess the stability and the suitability of perovskite materials for photovoltaics and, more generally, to help the development of advanced materials for energy applications. (65)
Biographies
Andrea Ciccioli
Andrea Ciccioli (born 1969) is a Senior Scientist at the Department of Chemistry of the University of Rome “La Sapienza”. His current research interests include the determination of thermodynamic properties of condensed phases by tensimetric measurements, the investigation of the evaporation/decomposition behavior of ionic liquids and hybrid materials, the experimental and computational study of bond energies of gaseous molecules.
Alessandro Latini
Alessandro Latini was born in Rome, Italy, in 1974. He obtained a Master degree in Chemistry and a Ph.D. in Chemical Sciences (2006) from the University of Rome “La Sapienza”, where he presently works as a Senior Scientist. His research is focused on the synthesis, characterization, and thermodynamic analysis of inorganic and hybrid materials, with special focus on advanced materials for energy conversion. He has coauthored 62 publications in international peer-reviewed journals.
Acknowledgments
Authors wish to thank warmly Dr. Eric V. Patterson (Stony Brook University, New York, USA) for sharing unpublished computational results on the CH3NH3I(g) dissociation reaction, and Prof. Rohan Mishra (Washington University in St. Louis, St. Louis, Missouri, USA) for providing numerical values of the theoretical decomposition enthalpies of CH3NH3PbX3. The work done by Mr. Niccolò Iacovelli in preparing Figure 1, 2, 5, and the TOC/abstract graphic is gratefully acknowledged.
References
This article references 65 other publications.
- 1Asghar, M. I.; Zhang, J.; Wang, H.; Lund, P. D. Device Stability of perovskite Solar Cells: A review. Renewable Sustainable Energy Rev. 2017, 77, 131– 146, DOI: 10.1016/j.rser.2017.04.003Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlvVOisbY%253D&md5=3c258ad2d58d9aa3609cdd636c97c6a8Device stability of perovskite solar cells - A reviewAsghar, M. I.; Zhang, J.; Wang, H.; Lund, P. D.Renewable & Sustainable Energy Reviews (2017), 77 (), 131-146CODEN: RSERFH; ISSN:1364-0321. (Elsevier Ltd.)A review. This work provides a thorough overview of state of the art of stability of perovskite solar cells (PSCs) and covers important degrdn. issues involved in this technol. Degrdn. factors, which are reported in the literature affecting the stability of PSCs, are discussed. Several degrdn. mechanisms resulting from thermal and chem. instabilities, phase transformations, exposure to visible and UV light, moisture and oxygen and most importantly sealing issues are thoroughly analyzed. Methods are suggested to study most of these degrdn. mechanisms in a systematic way. In addn., environmental assessment of PSCs is briefly covered. Alternative materials and their prepn. methods are screened with respect to stability of the device. Overall, this work contributes in developing better understanding of the degrdn. mechanisms and help in improving overall stability of the PSCs.
- 2Berhe, T. A.; Su, W.-N.; Chen, C.-H.; Pan, C.-J.; Cheng, J.-H.; Chen, H.-M.; Tsai, M.-C.; Chen, L.-Y.; Dubale, A. A.; Hwang, B.-J. Organometal Halide Perovskite Solar Cells: Degradation and Staility. Energy Environ. Sci. 2016, 9, 323– 356, DOI: 10.1039/C5EE02733KGoogle ScholarThere is no corresponding record for this reference.
- 3Manser, J. S.; Saidaminov, M. I.; Christians, J. A.; Bakr, O. M.; Kamat, P. V. Making and Breaking of Lead Halide Perovskites. Acc. Chem. Res. 2016, 49, 330– 338, DOI: 10.1021/acs.accounts.5b00455Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVyhsbc%253D&md5=da6db8049c1c2ef7e9e38e91ad064b6aMaking and Breaking of Lead Halide PerovskitesManser, Joseph S.; Saidaminov, Makhsud I.; Christians, Jeffrey A.; Bakr, Osman M.; Kamat, Prashant V.Accounts of Chemical Research (2016), 49 (2), 330-338CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review. A new front-runner has emerged in the field of next-generation photovoltaics. A unique class of materials, known as org. metal halide perovskites, bridges the gap between low-cost fabrication and exceptional device performance. These compds. can be processed at low temp. (typically in the range 80-150°) and readily self-assemble from the soln. phase into high-quality semiconductor thin films. The low energetic barrier for crystal formation has mixed consequences. On one hand, it enables inexpensive processing and both optical and electronic tunability. The caveat, however, is that many as-formed lead halide perovskite thin films lack chem. and structural stability, undergoing rapid degrdn. in the presence of moisture or heat. To date, improvements in perovskite solar cell efficiency have resulted primarily from better control over thin film morphol., manipulation of the stoichiometry and chem. of lead halide and alkylammonium halide precursors, and the choice of solvent treatment. Proper characterization and tuning of processing parameters can aid in rational optimization of perovskite devices. Likewise, gaining a comprehensive understanding of the degrdn. mechanism and identifying components of the perovskite structure that may be particularly susceptible to attack by moisture are vital to mitigate device degrdn. under operating conditions. This account provides insight into the life cycle of org.-inorg. lead halide perovskites, including (i) the nature of the precursor soln., (ii) formation of solid-state perovskite thin films and single crystals, and (iii) transformation of perovskites into hydrated phases upon exposure to moisture. In particular, spectroscopic and structural characterization techniques shed light on the thermally driven evolution of the perovskite structure. By tuning precursor stoichiometry and chem., and thus the lead halide charge-transfer complexes present in soln., crystn. kinetics can be tailored to yield improved thin film homogeneity. Because degrdn. of the as-formed perovskite film is in many ways analogous to its initial formation, the same suite of monitoring techniques reveals the moisture-induced transformation of low band gap methylammonium lead iodide (CH3NH3PbI3) to wide band gap hydrate compds. The rate of degrdn. is increased upon exposure to light. Interestingly, the hydration process is reversible under certain conditions. This facile formation and subsequent chem. lability raises the question of whether CH3NH3PbI3 and its analogs are thermodynamically stable phases, thus posing a significant challenge to the development of transformative perovskite photovoltaics. Adequately addressing issues of structural and chem. stability under real-world operating conditions is paramount if perovskite solar cells are to make an impact beyond the bench top. Expanding our fundamental knowledge of lead halide perovskite formation and degrdn. pathways can facilitate fabrication of stable, high-quality perovskite thin films for the next generation of photovoltaic and light emitting devices.
- 4Wang, D.; Wright, M.; Elumalai, N. K.; Uddin, A. Stability of perovskite Solar Cells. Solar Energy Mater. Sol. Energy Mater. Sol. Cells 2016, 147, 255– 275, DOI: 10.1016/j.solmat.2015.12.025Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlygtQ%253D%253D&md5=bbeb0a2e8c23923fcd88960e5a92dd92Stability of perovskite solar cellsWang, Dian; Wright, Matthew; Elumalai, Naveen Kumar; Uddin, AshrafSolar Energy Materials & Solar Cells (2016), 147 (), 255-275CODEN: SEMCEQ; ISSN:0927-0248. (Elsevier B.V.)The performance of perovskite solar cells has increased at an unprecedented rate, with efficiencies currently exceeding 20%. This technol. is particularly promising, as it is compatible with cheap soln. processing. For a thin-film solar product to be com. viable, it must pass the IEC 61646 testing stds., regarding the environmental stability. Currently, the poor stability of perovskite solar cells is a barrier to commercialization. The main issue causing this problem is the instability of the perovskite layer when in contact with moisture; however, it is important to explore stability problems with the other layers and interfaces within the device. The stability issues discussed in this review highlight the need to view the device as a whole system, due to the interdependent relationships between the layers, including: the perovskite absorber, electron transport layers, hole transport layers, other buffer layers and the electrodes. We also discuss other issues pertaining to device stability, such as measurement-induced hysteresis and the requirement for std. testing protocols. For perovskite solar cells to achieve the required stability, future research must focus on improving the intrinsic stability of the perovskite absorber layer, carefully designing the device geometry, and finding durable encapsulant materials, which seal the device from moisture.
- 5Leijtens, T.; Eperon, G. E.; Noel, N. K.; Habisreutinger, S. N.; Petrozza, A.; Snaith, H. J. Stability of Metal Halide Perovskite Solar Cells. Adv. Energy Mater. 2015, 5, 1500963, DOI: 10.1002/aenm.201500963Google ScholarThere is no corresponding record for this reference.
- 6Niu, G.; Guo, X.; Wang, L. Review of Recent Progress in Chemical Stability of Perovskite Solar Cells. J. Mater. Chem. A 2015, 3, 8970– 8980, DOI: 10.1039/C4TA04994BGoogle Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitVaqur%252FN&md5=1d6428e608a087ab03a54eb6d885c578Review of recent progress in chemical stability of perovskite solar cellsNiu, Guangda; Guo, Xudong; Wang, LiduoJournal of Materials Chemistry A: Materials for Energy and Sustainability (2015), 3 (17), 8970-8980CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)This review summarizes recent studies of the relationship of the chem. stability of perovskite solar cells with their environment (oxygen and moisture, UV light, soln. process, temp.) and corresponding possible solns. In recent years, the record efficiency of perovskite solar cells has been updated from 9.7% to 20.1%. However, there has been very little study of the issue of stability, which restricts the outdoor application of perovskite solar cells. The issues of the degrdn. of perovskite and the stability of perovskite solar cell devices should be urgently addressed to achieve good reproducibility and long lifetimes for perovskite solar cells with high conversion efficiency. Without studies on stability, exciting achievements cannot be transferred from the lab. to industry and outdoor applications. In order to improve their stability, a basic understanding of the degrdn. process of perovskite solar cells in different conditions should be acquired via thorough study.
- 7Ono, L. K.; Juarez-Perez, E. J.; Qi, Y. Progress on Perovskite Materials and Solar Cells with Mixed Cations and Halide Anions. ACS Appl. Mater. Interfaces 2017, 9, 30197– 30246, DOI: 10.1021/acsami.7b06001Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFaqsrjF&md5=4e3694cdf0a38b99b7a33d32d4442d43Progress on Perovskite Materials and Solar Cells with Mixed Cations and Halide AnionsOno, Luis K.; Juarez-Perez, Emilio J.; Qi, YabingACS Applied Materials & Interfaces (2017), 9 (36), 30197-30246CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)A review. Org.-inorg. halide perovskite materials (e.g. MAPbI3, FAPbI3, etc; where MA = CH3NH3+; FA = CH(NH2)2+) have been studied intensively for photovoltaic applications. Major concerns for the commercialization of perovskite photovoltaic technol. to take off include lead toxicity, long-term stability, hysteresis, and optimal bandgap. Therefore, there is still needs for further exploration of alternative candidates. Elemental compn. engineering of MAPbI3 and FAPbI3 has been proposed to address the above concerns. Among the best six certified power conversion efficiencies reported by National Renewable Energy Lab. (NREL) on perovskite-based solar cells, four are based on mixed perovskites (e.g. MAPbI1-xBrx, FA0.85MA0.15PbI2.55Br0.45, Cs0.1FA0.75MA0.15PbI2.49Br0.51). In this article, we review the recent progress on the synthesis and fundamental aspects of mixed cation and halide perovskites correlating with device performance, long-term stability, and hysteresis. In the outlook, we outline the future research directions based on the reported results as well as related topics that warrant further investigation.
- 8Chen, J.; Cai, X.; Yang, D.; Song, D.; Wang, J.; Jiang, J.; Ma, A.; Lv, S.; Hu, M. Z.; Ni, C. Recent Progress in Stabilizing Hybrid Perovskites for Solar Cell Applications. J. Power Sources 2017, 355, 98– 133, DOI: 10.1016/j.jpowsour.2017.04.025Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmtlKru74%253D&md5=9ebfaeda6b18c49c7f9bf149436d03c1Recent progress in stabilizing hybrid perovskites for solar cell applicationsChen, Jianqing; Cai, Xin; Yang, Donghui; Song, Dan; Wang, Jiajia; Jiang, Jinghua; Ma, Aibin; Lv, Shiquan; Hu, Michael Z.; Ni, ChaoyingJournal of Power Sources (2017), 355 (), 98-133CODEN: JPSODZ; ISSN:0378-7753. (Elsevier B.V.)A review is given. Hybrid inorg.-org. perovskites have quickly evolved as a promising group of materials for solar cells and optoelectronic applications mainly owing to the inexpensive materials, relatively simple and versatile fabrication and high power conversion efficiency (PCE). The certified energy conversion efficiency for perovskite solar cell (PSC) has reached above 20%, which is compatible to the current best for com. applications. However, long-term stabilities of the materials and devices remain to be the biggest challenging issue for realistic implementation of the PSCs. This article discusses the key issues related to the stability of perovskite absorbing layer including crystal structural stability, chem. stability under moisture, oxygen, illumination and interface reaction, effects of electron-transporting materials (ETM), hole-transporting materials (HTM), contact electrodes, ion migration and prepn. conditions. Towards the end, prospective strategies for improving the stability of PSCs are also briefly discussed and summarized. We focus on recent understanding of the stability of materials and devices and our perspectives about the strategies for the stability improvement.
- 9Slavney, A. H.; Smaha, R. W.; Smith, I. C.; Jaffe, A.; Umeyama, D.; Karunadasa, H. I. Chemical Approach to Addressing the Instability and Toxicity of Lead-Halide Perovskite Absorbers. Inorg. Chem. 2017, 56, 46– 55, DOI: 10.1021/acs.inorgchem.6b01336Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1ynsb7P&md5=903889ff9e5b8151fb5828a98de114e0Chemical Approaches to Addressing the Instability and Toxicity of Lead-Halide Perovskite AbsorbersSlavney, Adam H.; Smaha, Rebecca W.; Smith, Ian C.; Jaffe, Adam; Umeyama, Daiki; Karunadasa, Hemamala I.Inorganic Chemistry (2017), 56 (1), 46-55CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)A review. The impressive rise in efficiencies of solar cells employing the three-dimensional (3D) lead-iodide perovskite absorbers APbI3 (A = monovalent cation) has generated intense excitement. Although these perovskites have remarkable properties as solar-cell absorbers, their potential commercialization now requires a greater focus on the materials' inherent shortcomings and environmental impact. This creates a challenge and an opportunity for synthetic chemists to address these issues through the design of new materials. Synthetic chem. offers powerful tools for manipulating the magnificent flexibility of the perovskite lattice to expand the no. of functional analogs to APbI3. To highlight improvements that should be targeted in new materials, here we discuss the intrinsic instability and toxicity of 3D lead-halide perovskites. We consider possible sources of these instabilities and propose methods to overcome them through synthetic design. We also discuss new materials developed for realizing the exceptional photophys. properties of lead-halide perovskites in more environmentally benign materials. In this Forum Article, we provide a brief overview of the field with a focus on our group's contributions to identifying and addressing problems inherent to 3D lead-halide perovskites.
- 10Ito, S.; Tanaka, S.; Manabe, K.; Nishino, H. Effects of Surface Blocking Layer of Sb2S3 on Nanocrystalline TiO2 for CH3NH3PbI3 Perovskite Solar Cells. J. Phys. Chem. C 2014, 118, 16995– 17000, DOI: 10.1021/jp500449zGoogle Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXnt1amt7s%253D&md5=0b3efa8bca57ca6bf95ccefc79178b9aEffects of Surface Blocking Layer of Sb2S3 on Nanocrystalline TiO2 for CH3NH3PbI3 Perovskite Solar CellsIto, Seigo; Tanaka, Soichiro; Manabe, Kyohei; Nishino, HitoshiJournal of Physical Chemistry C (2014), 118 (30), 16995-17000CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Sb2S3 layers were inserted at the interface between TiO2 and CH3NH3PbI3 perovskite to create CH3NH3PbI3 solar cells using inorg. hole transporting material (CuSCN). The CH3NH3PbI3 layer was spin-coated by a one-drop method onto the nanocryst. TiO2 layer. The photoenergy conversion efficiencies were improved with Sb2S3 layers (the best efficiency: 5.24%). During the light exposure test without encapsulation, the CH3NH3PbI3 solar cells without Sb2S3 deteriorated to zero efficiency in 12 h and were completely changed from black to yellow because the perovskite CH3NH3PbI3 was changed to hexagonal PbI2. With Sb2S3, on the other hand, the CH3NH3PbI3 solar cells became stable against light exposure without encapsulation, which did not change the crystal structure or the wavelength edges of absorption and IPCE. Therefore, it was believed that degrdn. can occur at the interface between TiO2 and CH3NH3PbI3.
- 11Matteocci, F.; Cinà, L.; Lamanna, E.; Cacovich, S.; Divitini, G.; Midgley, P. A.; Ducati, C.; Di Carlo, A. Encapsulation for Long-Term Stability Enhancement of Perovskite Solar Cells. Nano Energy 2016, 30, 162– 172, DOI: 10.1016/j.nanoen.2016.09.041Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslWju73L&md5=775f04e1de37781f8eb65a12a288fd05Encapsulation for long-term stability enhancement of perovskite solar cellsMatteocci, Fabio; Cina, Lucio; Lamanna, Enrico; Cacovich, Stefania; Divitini, Giorgio; Midgley, Paul A.; Ducati, Caterina; Di Carlo, AldoNano Energy (2016), 30 (), 162-172CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)Perovskite Solar Cells (PSCs) have achieved power conversion efficiencies (PCEs) comparable to established technologies, but their stability in real-life working conditions - including exposure to moisture, heat and light - has still not been decisively demonstrated. Encapsulation of the cells is vital for increasing device lifetime, as well as shedding light on the intrinsic degrdn. process of the active layers. Here we compare different sealing protocols applied to large area cells (1 cm2, av. PCE 13.6%) to sep. the extrinsic degrdn., due to the external environment, from the intrinsic one, due to the materials themselves. Sealing methods were tested against accelerated life-time tests - damp-heating, prolonged heating and light-soaking. We thus developed and tested a novel sealing procedure that makes PSCs able to maintain a stabilized 10% PCE after heat, light and moisture stress.
- 12Huang, J.; Tan, S.; Lund, P. D.; Zhou, H. Impact of H2O on Organic-Inorganic Hybrid Perovskite Solar Cells. Energy Environ. Sci. 2017, 10, 2284– 2311, DOI: 10.1039/C7EE01674CGoogle Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFeqtrnL&md5=bdb1266b10f2a2d08ab9d54fa614b539Impact of H2O on organic-inorganic hybrid perovskite solar cellsHuang, Jianbing; Tan, Shunquan; Lund, Peter D.; Zhou, HuanpingEnergy & Environmental Science (2017), 10 (11), 2284-2311CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)The performance and stability of org.-inorg. hybrid perovskite solar cells (PSCs) is sensitive to water and moisture in an ambient environment. Understanding how H2O influences the perovskite material is also important for developing appropriate control strategies to mitigate the problem. Here we provide a comprehensive review on the effect of water on the state-of-the-art lead-based perovskite solar cells in terms of perovskite material design, perovskite film prepn., device fabrication, and photovoltaic application. It is found that a moderate amt. of water can facilitate nucleation and crystn. of the perovskite material, resulting in better perovskite film quality and enhanced PSC performance. The perovskite materials are irreversibly destroyed by H2O after a certain level of water, but they exihibit better tolerance than initially expected. Humidity resistant fabrication of high-performance PSC devices and modules should therefore be favored. Generally, water shows a neg. effect on the long-term stability and lifetime of PSCs. To reduce the effects from water during outdoor operation, attention should be paid to different protection methods such as varying the perovskite compn., optimizing the electron/hole transport layer and encapsulation of the device.
- 13Matsumoto, F.; Vorpahl, S. M.; Banks, J. Q.; Sengupta, E.; Ginger, D. S. Photodecomposition and Morphology Evolution of Organometal Halide Perovskite Solar Cells. J. Phys. Chem. C 2015, 119, 20810– 20816, DOI: 10.1021/acs.jpcc.5b06269Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtlOnur3O&md5=ef1e5d34b19586bbc37df0745a114983Photodecomposition and Morphology Evolution of Organometal Halide Perovskite Solar CellsMatsumoto, Fukashi; Vorpahl, Sarah M.; Banks, Jannel Q.; Sengupta, Esha; Ginger, David S.Journal of Physical Chemistry C (2015), 119 (36), 20810-20816CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)We study the photoinduced degrdn. of hybrid organometal perovskite photovoltaics under illumination and ambient atm. using UV-vis absorption, at. force microscopy, and device performance. We correlate the structural changes in the surface of the perovskite film with changes in the optical and electronic properties of the devices. The photodecompn. of the methylammonium lead triiodide perovskite layer itself proceeds much more slowly than the photodegrdn. of the performance of devices with fullerene/bathocuproine/aluminum top contacts, indicating that the active layer alone is more stable than the interface with the electrodes in this geometry. The evolution of the perovskite active layer performance proceeded through several phases: (1) an initial improvement in device characteristics, (2) a plateau with very slow degrdn., and (3) a catastrophic decline in material performance accompanied by marked changes in film morphol. The rapid increase in surface roughness of the active perovskite semiconductor assocd. with sudden failure also correlates with decreased absorption at the perovskite band edge and growth of a lead iodide absorption feature. We find that degrdn. requires both light and moisture, is accelerated at increased humidity, and scales linearly with light intensity, depending primarily on total photon dose.
- 14Poorkazem, K.; Kelly, T. L. Compositional Engineering to Improve the Stability of Lead Halide Perovskites: A comparative Study of Cationic and Anionic Dopants. ACS Appl. Energy Mater. 2018, 1, 181– 190, DOI: 10.1021/acsaem.7b00065Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFahsLbE&md5=0b3ae7117b83879d274f773eaaef01c4Compositional Engineering To Improve the Stability of Lead Halide Perovskites: A Comparative Study of Cationic and Anionic DopantsPoorkazem, Kianoosh; Kelly, Timothy L.ACS Applied Energy Materials (2018), 1 (1), 181-190CODEN: AAEMCQ; ISSN:2574-0962. (American Chemical Society)The instability of perovskite solar cells is the single greatest barrier to their commercialization. While a no. of studies have now looked at the effect of perovskite compn. on device stability, many of these have examd. only a single compositional variable. With many of these studies having been carried out under different environmental conditions, and still others lacking environmental controls entirely, it is often difficult to compare the relative effect of various cationic or anionic dopants. To address this knowledge gap, we fabricated CH3NH3PbI3-based solar cells where either the methylammonium or iodide ions were replaced with 20 mol % of a dopant ion (ethylammonium, formamidinium, bromide, or chloride). We then assessed their stability either in a controlled 85% relative humidity environment or under 1 sun illumination in air; both conditions have been previously shown to rapidly decomp. CH3NH3PbI3. Of the dopants studied, the formamidinium cations imparted the best moisture resistance, and the resulting perovskite displayed the lowest photochem. reactivity. We attribute the improved stability of the formamidinium-doped perovskite to the more delocalized pos. charge of the formamidinium cation.
- 15Ono, L. K.; Qi, Y. Surface and Interface Aspects of Organometal Halide Perovskite Materials and Solar Cells. J. Phys. Chem. Lett. 2016, 7, 4764– 4794, DOI: 10.1021/acs.jpclett.6b01951Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslGhtb7N&md5=2e5620e9175f7bac0fb949d8936225e9Surface and Interface Aspects of Organometal Halide Perovskite Materials and Solar CellsOno, Luis K.; Qi, YabingJournal of Physical Chemistry Letters (2016), 7 (22), 4764-4794CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)A review. The current challenges (e.g., stability, hysteresis, etc.) in organometal halide perovskite solar cell research are closely correlated with surfaces and interfaces. For instance, efficient generation of charges, extn., and transport with min. recombination through interlayer interfaces is crucial to attain high-efficiency solar cell devices. Furthermore, intralayer interfaces may be present in the form of grain boundaries within a film composed of the same material, for example, a polycryst. perovskite layer. The adjacent grains may assume different crystal orientations and/or have different chem. compns., which impacts charge excitation and dynamics and thereby the overall solar cell performance. In this Perspective, we present case studies to demonstrate (1) how surfaces and interfaces can impact material properties and device performance and (2) how these issues can be investigated by surface science techniques, such as scanning probe microscopy, photoelectron spectroscopy, and so forth. We end this Perspective by outlining the future research directions based on the reported results as well as the new trends in the field.
- 16Guerrero, A.; You, J.; Aranda, C.; Kang, Y. O.; Garcia-Belmonte, G.; Zhou, H.; Bisquert, J.; Yang, Y. Interfacial Degradation of Planar Lead Halide Perovskite Solar Cells. ACS Nano 2016, 10, 218– 224, DOI: 10.1021/acsnano.5b03687Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVeqt7jP&md5=74935f8cf4492ca73428599dcc7a100aInterfacial Degradation of Planar Lead Halide Perovskite Solar CellsGuerrero, Antonio; You, Jingbi; Aranda, Clara; Kang, Yong Soo; Garcia-Belmonte, Germa; Zhou, Huanping; Bisquert, Juan; Yang, YangACS Nano (2016), 10 (1), 218-224CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)The stability of perovskite solar cells is one of the major challenges for this technol. to reach commercialization, with water believed to be the major degrdn. source. In this work, a range of devices contg. different cathode metal contacts in the configuration ITO/PEDOT:PSS/MAPbI3/PCBM/Metal are fully elec. characterized before and after degrdn. caused by steady illumination during 4 h that induces a dramatic redn. in power conversion efficiency from values of 12 to 1.8%. We show that a decrease in performance and generation of the S-shape is assocd. with chem. degrdn. of the metal contact. Alternatively, use of Cr2O3/Cr as the contact enhances the stability, but modification of the energetic profile during steady illumination takes place, significantly reducing the performance. Several techniques including capacitance-voltage, X-ray diffraction, and optical absorption results suggest that the properties of the bulk perovskite layer are little affected in the device degrdn. process. Capacitance-voltage and impedance spectroscopy results show that the elec. properties of the cathode contact are being modified by generation of a dipole at the cathode that causes a large shift of the flat-band potential that modifies the interfacial energy barrier and impedes efficient extn. of electrons. Ionic movement in the perovskite layer changes the energy profile close to the contacts, modifying the energy level stabilization at the cathode. These results provide insights into the degrdn. mechanisms of perovskite solar cells and highlight the importance to further study the use of protecting layers to avoid the chem. reactivity of the perovskite with the external contacts.
- 17Huang, W.; Manser, J. S.; Kamat, P. V.; Ptasinska, S. Evolution of Chemical Composition, Morphology, and Photovoltaic Efficiency of CH3NH3PbI3 Perovskite under Ambient Conditions. Chem. Chem. Mater. 2016, 28, 303– 311, DOI: 10.1021/acs.chemmater.5b04122Google ScholarThere is no corresponding record for this reference.
- 18Koocher, N. Z.; Saldana-Greco, D.; Wang, F.; Liu, S.; Rappe, A. M. Polarization Dependenceof Water Adsoprtion to CH3NH3PbI3 (001). J. Phys. Chem. Lett. 2015, 6, 4371– 438, DOI: 10.1021/acs.jpclett.5b01797Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsF2ltbrF&md5=8365eb296bec95bac0e070840d90d7fdPolarization Dependence of Water Adsorption to CH3NH3PbI3 (001) SurfacesKoocher, Nathan Z.; Saldana-Greco, Diomedes; Wang, Fenggong; Liu, Shi; Rappe, Andrew M.Journal of Physical Chemistry Letters (2015), 6 (21), 4371-4378CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The instability of organometal halide perovskites when in contact with water is a serious challenge to their feasibility as solar cell materials. Although studies of moisture exposure have been conducted, an atomistic understanding of the degrdn. mechanism is required. Toward this goal, we study the interaction of water with the (001) surfaces of CH3NH3PbI3 under low and high water concns. using d. functional theory. We find that water adsorption is heavily influenced by the orientation of the methylammonium cations close to the surface. We demonstrate that, depending on methylammonium orientation, the water mol. can infiltrate into the hollow site of the surface and get trapped. Controlling dipole orientation via poling or interfacial engineering could thus enhance its moisture stability. No direct reaction between the water and methylammonium mols. is seen. Furthermore, calcns. with an implicit solvation model indicate that a higher water concn. may facilitate degrdn. through increased lattice distortion.
- 19Yuan, H.; Debroye, E.; Janssen, K.; Naiki, H.; Steuwe, C.; Lu, G.; Moris, M.; Orgiu, E.; Uji-I, H.; De Schryver, F.; Samorì, P. Degradation of Methylammonium Lead Iodide Perovskite Structures through Light and Electron Beam Driven Ion Migration. J. Phys. Chem. Lett. 2016, 7, 561– 566, DOI: 10.1021/acs.jpclett.5b02828Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1KmsLY%253D&md5=64250702d30988b4c910d636c1ee2e8eDegradation of Methylammonium Lead Iodide Perovskite Structures through Light and Electron Beam Driven Ion MigrationYuan, Haifeng; Debroye, Elke; Janssen, Kris; Naiki, Hiroyuki; Steuwe, Christian; Lu, Gang; Moris, Michele; Orgiu, Emanuele; Uji-i, Hiroshi; De Schryver, Frans; Samori, Paolo; Hofkens, Johan; Roeffaers, MaartenJournal of Physical Chemistry Letters (2016), 7 (3), 561-566CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Organometal halide perovskites show promising features for cost-effective application in photovoltaics. The material instability remains a major obstacle to broad application because of the poorly understood degrdn. pathways. Here, the authors apply simultaneous luminescence and electron microscopy on perovskites for the 1st time, allowing the authors to monitor in situ morphol. evolution and optical properties upon perovskite degrdn. Morphol., photoluminescence (PL), and cathodoluminescence of perovskite samples evolve differently upon degrdn. driven by electron beam (e-beam) or by light. A transversal elec. current generated by a scanning electron beam leads to dramatic changes in PL and tunes the energy band gaps continuously alongside film thinning. In contrast, light-induced degrdn. results in material decompn. to scattered particles and shows little PL spectral shifts. The differences in degrdn. can be ascribed to different elec. currents that drive ion migration. Also, soln.-processed perovskite cuboids show heterogeneity in stability which is likely related to crystallinity and morphol. The authors' results reveal the essential role of ion migration in perovskite degrdn. and provide potential avenues to rationally enhance the stability of perovskite materials by reducing ion migration while improving morphol. and crystallinity. It is worth noting that even moderate e-beam currents (86 pA) and acceleration voltages (10 kV) readily induce significant perovskite degrdn. and alter their optical properties. Therefore, attention has to be paid while characterizing such materials using SEM or TEM techniques.
- 20Philippe, B.; Park, B.-W.; Lindblad, R.; Oscarsson, J.; Ahmadi, S.; Johansson, E. M.; Rensmo, H. Chemical and Electronic Structure Characterization of Led Halide Perovskite and Stabilityi Behavior under Different Exposures – A Photoelectron Spectroscopy Investigation. Chem. Mater. 2015, 27, 1720– 1731, DOI: 10.1021/acs.chemmater.5b00348Google ScholarThere is no corresponding record for this reference.
- 21Akbulatov, A. F.; Luchkin, S. Yu.; Frolova, L. A.; Dremova, N. N.; Gerasimov, K. L.; Zhidkov, I. S.; Anokhin, A. V.; Kurmaev, E. Z.; Stevenson, K. J.; Troshin, P. A. Probing the Intrinsic Thermal and Photochemical Stability of Hybrid and Inorganic Lead Halide Perovskites. J. Phys. Chem. Lett. 2017, 8, 1211– 1218, DOI: 10.1021/acs.jpclett.6b03026Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjtVajtr0%253D&md5=06614bfefdafc451913bbde716b4e850Probing the Intrinsic Thermal and Photochemical Stability of Hybrid and Inorganic Lead Halide PerovskitesAkbulatov, Azat F.; Luchkin, Sergey Yu.; Frolova, Lyubov A.; Dremova, Nadezhda N.; Gerasimov, Kirill L.; Zhidkov, Ivan S.; Anokhin, Denis V.; Kurmaev, Ernst Z.; Stevenson, Keith J.; Troshin, Pavel A.Journal of Physical Chemistry Letters (2017), 8 (6), 1211-1218CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)We report a systematic study of thermal and photochem. degrdn. of a series of complex haloplumbates APbX3 (X =I, Br) with hybrid org. (A+ =CH3NH3) and inorg. (A+ =Cs+) cations under anoxic conditions (i.e., without exposure to O and moisture by testing in an inert glovebox environment). We show that the most common hybrid materials (e.g., MAPbI3) are intrinsically unstable with respect to the heat- and light-induced stress and, therefore, can hardly sustain the real solar cell operation conditions. On the contrary, the Ca-based all-inorg. complex Pb halides revealed far superior stability and, therefore, provide an impetus for creation of highly efficient and stable perovskite solar cells that can potentially achieve pragmatic operational benchmarks.
- 22Conings, B.; Drijkoningen, J.; Gauquelin, N.; Babayigit, A.; D’Haen, J.; D’Olieslaeger, L.; Ethirajan, A.; Verbeeck, J.; Manca, J.; Mosconi, E.; De Angelis, F.; Boyen, H.-G. Intrinsic Thermal Instability of Methylammonium Lead Trihalide Perovskite. Adv. Energy Mater. 2015, 5, 1500477, DOI: 10.1002/aenm.201500477Google ScholarThere is no corresponding record for this reference.
- 23Dualeh, A.; Gao, P.; Seok, S. I.; Nazeeruddin, M. K.; Grätzel, M. Thermal Behavior of Methyilammonium Lead-Trihalide Perovskite Photovoltaic Light Harvester. Chem. Mater. 2014, 26, 6160– 6164, DOI: 10.1021/cm502468kGoogle ScholarThere is no corresponding record for this reference.
- 24Alberti, A.; Deretzis, I.; Pellegrino, G.; Bongiorno, C.; Smecca, E.; Mannino, G.; Giannazzo, F.; Condorelli, G. G.; Sakai, N.; Miyasaka, T. Similar Structural Dynamics for the Degradation of CH3NH3PbI3 in Air and in Vacuum. ChemPhysChem 2015, 16, 3064– 3071, DOI: 10.1002/cphc.201500374Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVagtb%252FJ&md5=722011e314b057e4a64802930fd08c94Similar Structural Dynamics for the Degradation of CH3NH3PbI3 in Air and in VacuumAlberti, Alessandra; Deretzis, Ioannis; Pellegrino, Giovanna; Bongiorno, Corrado; Smecca, Emanuele; Mannino, Giovanni; Giannazzo, Filippo; Condorelli, Guglielmo Guido; Sakai, Nobuya; Miyasaka, Tsutomu; Spinella, Corrado; La Magna, AntoninoChemPhysChem (2015), 16 (14), 3064-3071CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)We investigate the degrdn. path of MAPbI3 (MA=methylammonium) films over flat TiO2 substrates at room temp. by means of x-ray diffraction, spectroscopic ellipsometry, XPS, and high-resoln. transmission electron microscopy. The degrdn. dynamics is found to be similar in air and under vacuum conditions, which leads to the conclusion that the occurrence of intrinsic thermodn. mechanisms is not necessarily linked to humidity. The process has an early stage, which drives the starting tetragonal lattice in the direction of a cubic at. arrangement. This early stage is followed by a phase change towards PbI2. We describe how this degrdn. product is structurally coupled with the original MAPbI3 lattice through the orientation of its constituent PbI6 octahedra. Our results suggest a slight octahedral rearrangement after volatilization of HI+CH3NH2 or MAI, with a relatively low energy cost. Our expts. also clarify why reducing the interfaces and internal defects in the perovskite lattice enhances the stability of the material.
- 25Ivanov, I. L.; Steparuk, A. S.; Bolyachkina, M. S.; Tsvetkov, D. S.; Safronov, A. P.; Zuev, A. Yu. Thermodynamics of formation of hybrid perovskite-type methylammonium lead halides. J. Chem. Thermodyn. 2018, 116, 253– 258, DOI: 10.1016/j.jct.2017.09.026Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFOhtrvO&md5=37b330bec5973df397ee028e95217d75Thermodynamics of formation of hybrid perovskite-type methylammonium lead halidesIvanov, I. L.; Steparuk, A. S.; Bolyachkina, M. S.; Tsvetkov, D. S.; Safronov, A. P.; Zuev, A. Yu.Journal of Chemical Thermodynamics (2018), 116 (), 253-258CODEN: JCTDAF; ISSN:0021-9614. (Elsevier Ltd.)Enthalpies of soln. of hybrid perovskites CH3NH3PbX3 (X = Cl, Br, I) in DMSO were measured using soln. calorimetry. Std. enthalpies and Gibbs free energies of formation of CH3NH3PbX3 (X = Cl, Br, I) hybrid perovskites from halides as well as from elements at 298 K were calcd. on the basis of exptl. data obtained and compared with the data available in literature. Excellent agreement was obtained between the std. Gibbs free energy of decompn. of CH3NH3PbX3 into solid PbX2, gaseous HX and methylamine calcd. on the basis of our data and that evaluated on the basis of vapor pressure measurement results reported by other authors. Entropy contribution was shown to play a major role in the stability of hybrid org.-inorg. perovskites with respect to their decompn. on constituent halides.
- 26Nagabhushana, G. P.; Shivaramaiah, R.; Navrotsky, A. Direct Calorimetric Verification of Thermodynamic Instability of Lead Halide Hybrid Perovskites. Proc. Natl. Acad. Sci. U. S. A. 2016, 113, 7717– 7721, DOI: 10.1073/pnas.1607850113Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFentrzM&md5=b3e3b2e535f04cdd69c9021aa7bb2d5aDirect calorimetric verification of thermodynamic instability of lead halide hybrid perovskitesNagabhushana, G. P.; Shivaramaiah, Radha; Navrotsky, AlexandraProceedings of the National Academy of Sciences of the United States of America (2016), 113 (28), 7717-7721CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Hybrid perovskites, esp. methylammonium lead iodide (MAPbI3), exhibit excellent solar power conversion efficiencies. However, their application is plagued by poor chem. and structural stability. Using direct calorimetric measurement of heats of formation, MAPbI3 is shown to be thermodynamically unstable with respect to decompn. to lead iodide and methylammonium iodide, even in the absence of ambient air or light or heat-induced defects, thus limiting its long-term use in devices. The formation enthalpy from binary halide components becomes less favorable in the order MAPbCl3, MAPbBr3, MAPbI3, with only the chloride having a neg. heat of formation. Optimizing the geometric match of constituents as measured by the Goldschmidt tolerance factor provides a potentially quantifiable thermodn. guide for seeking chem. substitutions to enhance stability.
- 27Brunetti, B.; Cavallo, C.; Ciccioli, A.; Gigli, G.; Latini, A. On the Thermal and Thermodynamic (In)stability of Methylammonium Lead Halide Perovskites. Sci. Rep. 2016, 6, 31896, DOI: 10.1038/srep31896Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVSrsb7N&md5=531e2461d5fd57c414ad5d9959bbd25cOn the Thermal and Thermodynamic (In)Stability of Methylammonium Lead Halide PerovskitesBrunetti, Bruno; Cavallo, Carmen; Ciccioli, Andrea; Gigli, Guido; Latini, AlessandroScientific Reports (2016), 6 (), 31896CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)The interest of the scientific community on methylammonium lead halide perovskites (MAPbX3, X = Cl, Br, I) for hybrid org.-inorg. solar cells has grown exponentially since the first report in 2009. This fact is clearly justified by the very high efficiencies attainable (reaching 20% in lab scale devices) at a fraction of the cost of conventional photovoltaics. However, many problems must be solved before a market introduction of these devices can be envisaged. Perhaps the most important to be addressed is the lack of information regarding the thermal and thermodn. stability of the materials towards decompn., which are intrinsic properties of them and which can seriously limit or even exclude their use in real devices. In this work we present and discuss the results we obtained using non-ambient X-ray diffraction, Knudsen effusion-mass spectrometry (KEMS) and Knudsen effusion mass loss (KEML) techniques on MAPbCl3, MAPbBr3 and MAPbI3. The measurements demonstrate that all the materials decomp. to the corresponding solid lead (II) halide and gaseous methylamine and hydrogen halide, and the decompn. is well detectable even at moderate temps. (∼60 °C). Our results suggest that these materials may be problematic for long term operation of solar devices.Brunetti, B.; Cavallo, C.; Ciccioli, A.; Gigli, G.; Latini, A. Corrigendum: On the Thermal and Thermodynamic (In)Stability of Methylammonium Lead Halide Perovskites. Sci. Rep 2017, 7, 46867, DOI: 10.1038/srep46867Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1Cms7fL&md5=f8549c08001b340d933daea262c93f84Corrigendum: On the Thermal and Thermodynamic (In)Stability of Methylammonium Lead Halide PerovskitesBrunetti, Bruno; Cavallo, Carmen; Ciccioli, Andrea; Gigli, Guido; Latini, AlessandroScientific Reports (2017), 7 (), 46867CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)There is no expanded citation for this reference.
- 28Thind, A. S.; Huang, X.; Sun, J.; Mishra, R. First-Principle Prediction of a Stable Hexagonal Phase of CH3NH3PbI3. Chem. Mater. 2017, 29, 6003– 6011, DOI: 10.1021/acs.chemmater.7b01781Google ScholarThere is no corresponding record for this reference.
- 29Faghihnasiri, M.; Izadifard, M.; Ghazi, M. E. DFT Study of Mechanical Properties and Stability of Cubic Methylammonium Lead Halide Perovskites (CH3NH3PbX3, X = I, Br, Cl). J. Phys. Chem. C 2017, 121, 27059– 27070, DOI: 10.1021/acs.jpcc.7b07129Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslyhsrrI&md5=420bd1c0c18850d468a88ee52206899cDFT Study of Mechanical Properties and Stability of Cubic Methylammonium Lead Halide Perovskites (CH3NH3PbX3, X = I, Br, Cl)Faghihnasiri, Mahdi; Izadifard, Morteza; Ghazi, Mohammad EbrahimJournal of Physical Chemistry C (2017), 121 (48), 27059-27070CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)In this study, using the d. functional theory, the mech. properties of methylammonium lead halide perovskites (CH3NH3PbX3, X = I, Br, Cl) were investigated. Young's modulus, bulk modulus, and shear modulus, Poisson's ratio, and many other parameters were calcd. using the PBEsol and vdW approxns. Also, in this work, utilizing a new accuracy in calcg. the elastic consts., the intense conflict between the previous theor. results and the exptl. data were fixed. Moreover, for the first time, through combination of the PBEsol and vdW methods, the effect of the interaction between methylammonium and PbX3 scaffold on the mech. properties of lead halide perovskites was well cleared. In continuation, using the PBEsol+vdW method, a phase transition appeared for the MAPbBr3 and MAPbCl3 structures, which proved more stability of MAPbBr3 and MAPbCl3 in comparison with MAPbI3. In what follows, by studying these materials under an applied strain beyond the harmonic region, the transition zone to the plastic area in the strain region of 5.5% and smaller was identified, and the small values of the aforementioned applied strains were found to be the reason for the instability of these materials at room temp. and above.
- 30Yang, D.; Lv, J.; Zhao, X.; Xu, Q.; Fu, Y.; Zhan, F.; Zunger, A.; Zhang, L. Functionality-Directed Screening of Pb-Free Hybrid Organic-Inorganic Perovskites with Desired Intrinsic Photovoltaic Functionalities. Chem. Mater. 2017, 29, 524– 538, DOI: 10.1021/acs.chemmater.6b03221Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitFOiurzI&md5=a081b09283f5c1cb70acc487384d6c98Functionality-Directed Screening of Pb-Free Hybrid Organic-Inorganic Perovskites with Desired Intrinsic Photovoltaic FunctionalitiesYang, Dongwen; Lv, Jian; Zhao, Xingang; Xu, Qiaoling; Fu, Yuhao; Zhan, Yiqiang; Zunger, Alex; Zhang, LijunChemistry of Materials (2017), 29 (2), 524-538CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The material class of hybrid org.-inorg. perovskites has risen rapidly from a virtually unknown material in photovoltaic applications a short 7 years ago into an ∼20% efficient thin-film solar cell material. As promising as this class of materials is, however, there are limitations assocd. with its poor long-term stability, nonoptimal band gap, presence of environmentally toxic Pb element, etc. We herein apply a functionality-directed theor. materials selection approach as a filter for initial screening of the compds. that satisfy the desired intrinsic photovoltaic functionalities and might overcome the above limitations. First-principles calcns. are employed to systemically study thermodn. stability and photovoltaic-related properties of hundreds of candidate hybrid perovskites. We have identified in this materials selection process 14 Ge- and Sn-based materials with potential superior bulk-material-intrinsic photovoltaic performance. A distinct class of compds. contg. NH3COH+ with the org. mol. derived states intriguingly emerging at band-edges is found. Comparison of various candidate materials offers insights on how compn. variation and microscopic structural changes affect key photovoltaic relevant properties in this family of materials.
- 31Buin, A.; Comin, R.; Xu, J.; Ip, A. H.; Sargent, E. H. Halide-Dependent Electronic Structure of Organolead Perovskite Materials. Chem. Mater. 2015, 27, 4405– 4412, DOI: 10.1021/acs.chemmater.5b01909Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXpsFOitbo%253D&md5=0cca5a4d89cdea2cebf27e91a8a51cc8Halide-Dependent Electronic Structure of Organolead Perovskite MaterialsBuin, Andrei; Comin, Riccardo; Xu, Jixian; Ip, Alexander H.; Sargent, Edward H.Chemistry of Materials (2015), 27 (12), 4405-4412CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)Organometal halide perovskites have recently attracted tremendous attention both at the exptl. and theor. levels. These materials, in particular methylammonium triiodide, are still limited by poor chem. and structural stability under ambient conditions. Today this represents one of the major challenges for polycryst. perovskite-based photovoltaic technol. In addn. to this, the performance of perovskite-based devices is degraded by deep localized states, or traps. To achieve better-performing devices, it is necessary to understand the nature of these states and the mechanisms that lead to their formation. The major sources of deep traps in the different halide systems have different origin and character. Halide vacancies are shallow donors in I-based perovskites, whereas they evolve into a major source of traps in Cl-based perovskites. Lead interstitials, which can form lead dimers, are the dominant source of defects in Br-based perovskites, in line with recent exptl. data. As a result, the optimal growth conditions are also different for the distinct halide perovskites: growth should be halide-rich for Br and Cl, and halide-poor for I-based perovskites. Stability in relation to the reaction enthalpies of mixts. of bulk precursors with respect to final perovskite product are discussed. Methylammonium lead triiodide was characterized by the lowest reaction enthalpy, explaining its low stability. At the opposite end, the highest stability was found for the methylammonium lead trichloride, also consistent with the authors' exptl. findings which show no observable structural variations over an extended period of time.
- 32Zhang, Y.-Y.; Chen, S.; Xu, P.; Xiang, H.; Gong, X.-G.; Walsh, A.; Wei, S.-H. Intrinsic Instability of the Hybrid Halide Perovskite Semiconductor CH3NH3PbI3. arXiv.org, e-Print Arch., Condens. Matter 2015, arXiv:1506.01301 DOI: 10.1088/0256-307X/35/3/036104Google ScholarThere is no corresponding record for this reference.
- 33Buin, A.; Pietsch, P.; Xu, J.; Voznyy, O.; Ip, A. H.; Comin, R.; Sargent, E. H. Materials Processing Routes to Trap-Free Halide Perovskites. Nano Lett. 2014, 14, 6281– 6286, DOI: 10.1021/nl502612mGoogle Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslagurzF&md5=c0f902453e55d5a93ec2bf3cded2224eMaterials Processing Routes to Trap-Free Halide PerovskitesBuin, Andrei; Pietsch, Patrick; Xu, Jixian; Voznyy, Oleksandr; Ip, Alexander H.; Comin, Riccardo; Sargent, Edward H.Nano Letters (2014), 14 (11), 6281-6286CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Photovoltaic devices based on lead iodide perovskite films have seen rapid advancements, recently achieving an impressive 17.9% certified solar power conversion efficiency. Reports have consistently emphasized that the specific choice of growth conditions and chem. precursors is central to achieving superior performance from these materials; yet the roles and mechanisms underlying the selection of materials processing route is poorly understood. Films grown under iodine-rich conditions are prone to a high d. of deep electronic traps (recombination centers), while the use of a chloride precursor avoids the formation of key defects (Pb atom substituted by I) responsible for short diffusion lengths and poor photovoltaic performance. Also, the lowest-energy surfaces of perovskite crystals are entirely trap-free, preserving both electron and hole delocalization to a remarkable degree, helping to account for explaining the success of polycryst. perovskite films. The authors construct perovskite films from I-poor conditions using a lead acetate precursor, and the authors' measurement of a long (600 ± 40 nm) diffusion length confirms this new picture of the importance of growth conditions.
- 34Tenuta, E.; Zheng, C.; Rubel, O. Thermodynamic Origin of Instability in Hybrid Halide Perovskites. Sci. Rep. 2016, 6, 37654, DOI: 10.1038/srep37654Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitFSmtbvJ&md5=cdf310db5f6822b0dea11f0b16d9a978Thermodynamic origin of instability in hybrid halide perovskitesTenuta, E.; Zheng, C.; Rubel, O.Scientific Reports (2016), 6 (), 37654CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)Degrdn. of hybrid halide perovskites under the influence of environmental factors impairs future prospects of using these materials as absorbers in solar cells. First principle calcns. can be used as a guideline in search of new materials, provided we can rely on their predictive capabilities. We show that the instability of perovskites can be captured using ab initio total energy calcns. for reactants and products augmented with addnl. thermodn. data to account for finite temp. effects. Calcns. suggest that the instability of CH3NH3PbI3 in moist environment is linked to the aq. soly. of the CH3NH3I salt, thus making other perovskite materials with sol. decompn. products prone to degrdn. Properties of NH3OHPbI3, NH3NH2PbI3, PH4PbI3, SbH4PbI3, CsPbBr3, and a new hypothetical SF3PbI3 perovskite are studied in the search for alternative solar cell absorber materials with enhanced chem. stability.
- 35Ganose, A. M.; Savory, C. N.; Scanlon, D. O. (CH3NH3)2Pb(SCN)2I2: A More Stable Structural Motif for Hybrid Halide Photovoltaics ?. J. Phys. Chem. Lett. 2015, 6, 4594– 4598, DOI: 10.1021/acs.jpclett.5b02177Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhslGms7bK&md5=7cb162d005a67d7418b9ef5ee761df6f(CH3NH3)2Pb(SCN)2I2: A New More Stable Structural Motif for Hybrid Halide Photovoltaics?Ganose, Alex M.; Savory, Christopher N.; Scanlon, David O.Journal of Physical Chemistry Letters (2015), 6 (22), 4594-4598CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Hybrid halide perovskites have recently emerged as a highly efficient class of light absorbers; however, there are increasing concerns over their long-term stability. Recently, incorporation of SCN- was suggested as a novel route to improving stability without neg. impacting performance. Intriguingly, despite crystg. in a 2-dimensional layered structure, (CH3NH3)2Pb(SCN)2I2 (MAPSI) possesses an ideal band gap of 1.53 eV, close to that of the 3-dimensional connected champion hybrid perovskite absorber, CH3NH3PbI3 (MAPI). Here, the authors identify, using hybrid d. functional theory, the origin of the smaller than expected band gap of MAPSI through a detailed comparison with the electronic structure of MAPI. Also, assessment of the MAPSI structure reveals that it is thermodynamically stable with respect to phase sepn., a likely source of the increased stability reported in expt.
- 36Zheng, C.; Rubel, O. Ionization Energy as a Stability Criterion for Halide Perovskites. J. Phys. Chem. C 2017, 121, 11977– 11984, DOI: 10.1021/acs.jpcc.7b00333Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXns1Ontrs%253D&md5=e050eee4490f3cecf84aa925113e1c95Ionization Energy as a Stability Criterion for Halide PerovskitesZheng, Chao; Rubel, OlegJournal of Physical Chemistry C (2017), 121 (22), 11977-11984CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Instability of hybrid org.-inorg. halide perovskites hinders their development for photovoltaic applications. First-principles calcns. were used for evaluation of a decompn. reaction enthalpy of hybrid halide perovskites, which is linked to exptl. obsd. degrdn. of device characteristics. However, simple criteria for predicting the intrinsic stability of halide perovskites are lacking since Goldschmidt's tolerance and octahedral geometrical factors do not fully capture formability of those perovskites. The authors extend the Born-Haber cycle to partition the reaction enthalpy of various perovskite structures into lattice, ionization, and molecularization energy components. The anal. of various contributions to the reaction enthalpy points to an ionization energy of an org. mol. and an inorg. complex ion as an addnl. criterion for predicting chem. trends in stability of hybrid halide perovskites. The ionization energy equal to or less than that for cesium and the size comparable to that of methylammonium define the design space for cations A+ in the search for new perovskite structures APbI3 with improved chem. stability that are suitable for photovoltaic applications.
- 37Yang, B.; Dyck, O.; Ming, W.; Du, M.-H.; Das, S.; Rouleau, C. M.; Duscher, G.; Geohegan, D. B.; Xiao, K. Observation of Nanoscale Morphological and Structural Degradation in Perovskite Solar Cells by in Situ TEM. ACS Appl. Mater. Interfaces 2016, 8, 32333– 32340, DOI: 10.1021/acsami.6b11341Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvVSjur7M&md5=3c22e4bc4468498904d7a761cbdd0293Observation of Nanoscale Morphological and Structural Degradation in Perovskite Solar Cells by in Situ TEMYang, Bin; Dyck, Ondrej; Ming, Wenmei; Du, Mao-Hua; Das, Sanjib; Rouleau, Christopher M.; Duscher, Gerd; Geohegan, David B.; Xiao, KaiACS Applied Materials & Interfaces (2016), 8 (47), 32333-32340CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)High-resoln. in situ transmission electron microscopy (TEM) and electron energy loss spectroscopy were applied to systematically investigate morphol. and structural degrdn. behaviors in perovskite films during different environmental exposure treatments. In situ TEM expt. indicates that vacuum itself is not likely to cause degrdn. in perovskites. In addn., these materials were found to degrade significantly when they were heated to ∼50-60 °C (i.e., a solar cell's field operating temp.) under illumination. This observation thus conveys a critically important message that the instability of perovskite solar cells at such a low temp. may limit their real field com. applications. It was further unveiled that oxygen most likely attacks the CH3NH3+ org. moiety rather than the PbI6 component of perovskites during ambient air exposure at room temp. This finding grants a deeper understanding of the perovskite degrdn. mechanism and suggests a way to prevent degrdn. of perovskites by tailoring the org. moiety component.
- 38Agiorgousis, M. L.; Sun, Y.-Y.; Zeng, A.; Zhang, S. Strong Covalency-Induced Recombination Centers in Perovskite Solar Cell Material CH3NH3PbI3. J. Am. Chem. Soc. 2014, 136, 14570– 14575, DOI: 10.1021/ja5079305Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsFyjtbnE&md5=6231d3e9862a08628d8eebe695356b68Strong Covalency-Induced Recombination Centers in Perovskite Solar Cell Material CH3NH3PbI3Agiorgousis, Michael L.; Sun, Yi-Yang; Zeng, Hao; Zhang, ShengbaiJournal of the American Chemical Society (2014), 136 (41), 14570-14575CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Inorg.-org. hybrid perovskites are a new family of solar cell materials, which have recently been used to make solar cells with efficiency approaching 20%. Here, we report the unique defect chem. of the prototype material, CH3NH3PbI3, based on first-principles calcn. We found that both the Pb cations and I anions in this material exhibit strong covalency as characterized by the formation of Pb dimers and I trimers with strong covalent bonds at some of the intrinsic defects. The Pb dimers and I trimers are only stabilized in a particular charge state with significantly lowered energy, which leads to deep charge-state transition levels within the band gap, in contradiction to a recent proposal that this system has only shallow intrinsic defects. Our results show that, in order to prevent the deep-level defects from being effective recombination centers, the equil. carrier concns. should be controlled so that the Fermi energy is about 0.3 eV away from the band edges. Beyond this range, according to a Shockley-Read-Hall anal., the nonequil. carrier lifetime will be strongly affected by the concn. of I vacancies and the anti-site defects with I occupying a CH3NH3 site.
- 39Haruyama, J.; Sodeyama, K.; Han, L.; Tateyama, Y. Termination Dependence of Tetragonal CH3NH3PbI3 Surfaces for Perovskite Solar Cells. J. Phys. Chem. Lett. 2014, 5, 2903– 2909, DOI: 10.1021/jz501510vGoogle Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtleqtLfO&md5=45b2397926d439305279faad86275965Termination Dependence of Tetragonal CH3NH3PbI3 Surfaces for Perovskite Solar CellsHaruyama, Jun; Sodeyama, Keitaro; Han, Liyuan; Tateyama, YoshitakaJournal of Physical Chemistry Letters (2014), 5 (16), 2903-2909CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)We investigated the termination dependence of structural stability and electronic states of the representative (110), (001), (100), and (101) surfaces of tetragonal CH3NH3PbI3 (MAPbI3), the main component of a perovskite solar cell (PSC), by d. functional theory calcns. By examg. various types of PbIx polyhedron terminations, we found that a vacant termination is more stable than flat termination on all of the surfaces, under thermodn. equil. conditions of bulk MAPbI3. More interestingly, both terminations can coexist esp. on the more probable (110) and (001) surfaces. The electronic structures of the stable vacant and PbI2-rich flat terminations on these two surfaces largely maintain the characteristics of bulk MAPbI3 without midgap states. Thus, these surfaces can contribute to the long carrier lifetime actually obsd. for the PSCs. Furthermore, the shallow surface states on the (110) and (001) flat terminations can be efficient intermediates of hole transfer. Consequently, the formation of the flat terminations under the PbI2-rich condition will be beneficial for the improvement of PSC performance.
- 40Yin, W.- J.; Shi, T.; Yan, Y. Unusual Defect Physics in CH3NH3PbI3 Perovskite Solar Cell Absorbers. Appl. Phys. Lett. 2014, 104, 063903, DOI: 10.1063/1.4864778Google ScholarThere is no corresponding record for this reference.
- 41Onoda-Yamamuro, N.; Matsuo, T.; Suga, H. Calorimetric and IR Spectroscopic Studies of Phase Transitions in Methylammonium Trihalogenoplumbates (II). J. Phys. Chem. Solids 1990, 51, 1383– 1395, DOI: 10.1016/0022-3697(90)90021-7Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXhtFahsL4%253D&md5=e87ac8ccd0e391890852451c44f992d9Calorimetric and IR spectroscopic studies of phase transitions in methylammonium trihaloplumbates(II)Onoda-Yamamuro, Noriko; Matsuo, Takasuke; Suga, HiroshiJournal of Physics and Chemistry of Solids (1990), 51 (12), 1383-95CODEN: JPCSAW; ISSN:0022-3697.Heat capacities of CH3NH3PbX3(X = Cl, Br, I) were measured at 13-300 K (365 K for the I). Two anomalies were found in the Cl and the I, and 3 in the Br. All the phase transitions were of the 1st order, although the highest temp. transitions in the Br and the I were close to 2nd order. Their temps. and entropies are given.
- 42Glasser, L.; Jenkins, D. D. B. Standard Absolute Entropies, S°298, from Volume or Density. Part II. Organic Liquids and Solids. Thermochim. Acta 2004, 414, 125– 130, DOI: 10.1016/j.tca.2003.12.006Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXjsVCrsb4%253D&md5=d7870a85fb38d213e185774ea460490dStandard absolute entropies, S298°, from volume or density. Part II. Organic liquids and solidsGlasser, Leslie; Jenkins, H. Donald BrookeThermochimica Acta (2004), 414 (2), 125-130CODEN: THACAS; ISSN:0040-6031. (Elsevier Science B.V.)The std. abs. entropies of many materials are unknown, which precludes a full understanding of their thermodn. stabilities. We show, for both org. liqs. and solids, that entropies are reliably linearly correlated with vol. per mol., Vm (nm3 per mol.) (or molar volume, M/ρ (cm3 mol-1)); thus, permitting simple evaluation of std. entropies (J K-1 mol-1) at 298 K. The regression lines generally pass close to the origin, with the following formulas: for org. liqs., S298°(l) (J K-1 mol-1) = 1133Vm + 44 or S298°(l) (J K-1 mol-1) = 1.881M/ρ + 44; for org. solids, S298°(s) (J K-1 mol-1) = 774Vm + 57 or S298°(s) (J K-1 mol-1) = 1.285M/ρ + 57. These results complement similar studies (by ourselves and others) demonstrating linear entropy-vol. correlations for ionic solids (including minerals, simple ionic solids, and ionic hydrates and solvates).
- 43El-Mellouhi, F.; Bentria, E. T.; Rashkeev, S. N.; Kais, S.; Alharbi, F. H. Enhancing Intrinsic Stability of Hybrid Perovskite Sola Cell by Strong, yet Balanced, Electronic Coupling. Sci. Rep. 2016, 6, 30305, DOI: 10.1038/srep30305Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht12gu7vI&md5=c35c71967d3bc68788806f8e738b47d2Enhancing Intrinsic Stability of Hybrid Perovskite Solar Cell by Strong, yet Balanced, Electronic CouplingEl-Mellouhi, Fedwa; Bentria, El Tayeb; Rashkeev, Sergey N.; Kais, Sabre; Alharbi, Fahhad H.Scientific Reports (2016), 6 (), 30305CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)In the past few years, the meteoric development of hybrid org.-inorg. perovskite solar cells (PSC) astonished the community. The efficiency has already reached the level needed for commercialization; however, the instability hinders its deployment on the market. Here, we report a mechanism to chem. stabilize PSC absorbers. We propose to replace the widely used methylammonium cation (CH3NH3+) by alternative mol. cations allowing an enhanced electronic coupling between the cation and the PbI6 octahedra while maintaining the band gap energy within the suitable range for solar cells. The mechanism exploits establishing a balance between the electronegativity of the materials' constituents and the resulting ionic electrostatic interactions. The calcns. demonstrate the concept of enhancing the electronic coupling, and hence the stability, by exploring the stabilizing features of CH3PH3+, CH3SH2+, and SH3+ cations, among several other possible candidates. Chem. stability enhancement hence results from a strong, yet balanced, electronic coupling between the cation and the halides in the octahedron. This shall unlock the hindering instability problem for PSCs and allow them to hit the market as a serious low-cost competitor to silicon based solar cell technologies.
- 44Chun-Ren Ke, J.; Walton, A. S.; Lewis, D. J.; Tedstone, A.; O’Brien, P.; Thomas, A. G.; Flavell, W. R. In situ Investigation of Degradation at Organometal Halide Perovskite Surfaces by X-Ray Photoeectron Spectroscopy at Realistic Water Vapour Pressure. Chem. Commun. 2017, 53, 5231, DOI: 10.1039/C7CC01538KGoogle ScholarThere is no corresponding record for this reference.
- 45Hong, F.; Saparov, B.; Meng, W.; Xiao, Z.; Mitzi, D. B.; Yan, Y. Viability of Lead-Free Perovskites with Mixed Chalcogen and Halogen Anions for Photovoltaic Applications. J. Phys. Chem. C 2016, 120, 6435– 6441, DOI: 10.1021/acs.jpcc.6b00920Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjvVGjsrw%253D&md5=fa35a1bdcc705c34cbcc9d79fbe3166fViability of Lead-Free Perovskites with Mixed Chalcogen and Halogen Anions for Photovoltaic ApplicationsHong, Feng; Saparov, Bayrammurad; Meng, Weiwei; Xiao, Zewen; Mitzi, David B.; Yan, YanfaJournal of Physical Chemistry C (2016), 120 (12), 6435-6441CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The authors assess the viability for photovoltaic applications of proposed Pb-free perovskites with mixed chalcogen and halogen anions, AB(Ch,X)3 (A = Cs or Ba; B = Sb or Bi; Ch = chalcogen; X = halogen), by examg. crit. issues such as the structural, electronic/optical properties, and stability through the combination of d.-functional theory calcns. and solid-state reactions. The calcns. show that these quaternary Pb-free perovskites are thermodynamically unstable-they are prone to decomp. into ternary and/or binary secondary phases or form phases with nonperovskite structures. Solid-state synthesis efforts confirm the theor. predicted difficulty for prepg. these compds.; all attempted reactions do not form the desired perovskite phases with mixed chalcogen and halogen anions under conditions examd. Instead, they form sep. binary and ternary compds. Despite earlier predictions of promising characteristics for these prospective perovskites for photovoltaics, the results suggest that, due to their instability, the Pb-free perovskites with mixed chalcogen and halogen anions may be challenging to form under equil. synthetic conditions.
- 46Kim, N.-K.; Min, Y. H.; Noh, S.; Cho, E.; Jeong, G.; Joo, M.; Ahn, S.-W.; Lee, J. S.; Kim, S.; Ihm, K.; Ahn, H. Investigation of Thermally Induced Degradation in CH3NH3PbI3 Perovskite Solar Cells Using In-situ Synchrotron Radiation Analysis. Sci. Rep. 2017, 7, 4645, DOI: 10.1038/s41598-017-04690-wGoogle Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1cjkvVWksA%253D%253D&md5=3799e89322ddb5bfd60f8da2263cc716Investigation of Thermally Induced Degradation in CH3NH3PbI3 Perovskite Solar Cells using In-situ Synchrotron Radiation AnalysisKim Nam-Koo; Min Young Hwan; Noh Seokhwan; Cho Eunkyung; Jeong Gitaeg; Joo Minho; Ahn Seh-Won; Lee Jeong Soo; Kim Seongtak; Kang Yoonmook; Lee Hae-Seok; Kim Donghwan; Ihm Kyuwook; Ahn HyungjuScientific reports (2017), 7 (1), 4645 ISSN:.In this study, we employ a combination of various in-situ surface analysis techniques to investigate the thermally induced degradation processes in MAPbI3 perovskite solar cells (PeSCs) as a function of temperature under air-free conditions (no moisture and oxygen). Through a comprehensive approach that combines in-situ grazing-incidence wide-angle X-ray diffraction (GIWAXD) and high-resolution X-ray photoelectron spectroscopy (HR-XPS) measurements, we confirm that the surface structure of MAPbI3 perovskite film changes to an intermediate phase and decomposes to CH3I, NH3, and PbI2 after both a short (20 min) exposure to heat stress at 100 °C and a long exposure (>1 hour) at 80 °C. Moreover, we observe clearly the changes in the orientation of CH3NH3(+) organic cations with respect to the substrate in the intermediate phase, which might be linked directly to the thermal degradation processes in MAPbI3 perovskites. These results provide important progress towards improved understanding of the thermal degradation mechanisms in perovskite materials and will facilitate improvements in the design and fabrication of perovskite solar cells with better thermal stability.
- 47Song, Z.; Watthage, S. C.; Phillips, A. B.; Tompkins, B. L.; Ellingson, R. J.; Heben, M. J. Impact of Processing Temperature and Composition on the Formation of Methylammonium Lead Iodide Perovskites. Chem. Mater. 2015, 27, 4612– 4619, DOI: 10.1021/acs.chemmater.5b01017Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXosVCgsrs%253D&md5=ecce420966bae0b8ca34931601860181Impact of Processing Temperature and Composition on the Formation of Methylammonium Lead Iodide PerovskitesSong, Zhaoning; Watthage, Suneth C.; Phillips, Adam B.; Tompkins, Brandon L.; Ellingson, Randy J.; Heben, Michael J.Chemistry of Materials (2015), 27 (13), 4612-4619CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)A delicate control of the stoichiometry, crystallog. phase, and grain structure of the photoactive material is typically required to fabricate high-performance photovoltaic (PV) devices. Organo-metal halide perovskite materials, however, exhibit a large degree of tolerance in synthesis and can be fabricated into high efficiency devices by a variety of different vacuum and soln.-based processes, with a wide range of precursor ratios. Probably the phase field for the desired material is wider than expected or that high device efficiency may be achieved with a range of phases. Here, the authors study the structural and optical properties of the materials formed when a range of compns. of methylammonium iodide (MAI) and lead iodide (PbI2) were reacted at 40-190°. The reactions were performed according to a commonly employed synthetic approach for high efficiency PV devices, and the data was analyzed to construct a pseudobinary, temp.-dependent, phase-compn. processing diagram. Escape of MAI vapor at the highest temps. (150-190°) enabled a PbI2 phase to persist to very high MAI concns., and the processing diagram was not representative of phase equil. in this range. Data from reactions performed with a fixed vapor pressure of MAI allowed the high temp. portion of the diagram to be cor. and a near-equil. phase diagram to be proposed. The perovskite phase field is wider than previously thought under both processing conditions and extended by the existence of stacked perovskite sheet phases. Several aspects of the diagrams clarify why the organo-halide perovskite materials are compatible with soln. processing.
- 48Leyden, M. R.; Meng, L.; Jiang, Y.; Ono, L. K.; Qiu, L.; Juarez-Perez, E. J.; Qin, C.; Adachi, C.; Qi, Y. Methylammonium Lead Bromide Perovskite Light-Emitting Diodes by Chemical Vapor deposition. J. Phys. Chem. Lett. 2017, 8, 3193– 3198, DOI: 10.1021/acs.jpclett.7b01093Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVKisbrL&md5=96c91cb7f5f53c11ec06d701646a11cdMethylammonium Lead Bromide Perovskite Light-Emitting Diodes by Chemical Vapor DepositionLeyden, Matthew R.; Meng, Lingqiang; Jiang, Yan; Ono, Luis K.; Qiu, Longbin; Juarez-Perez, Emilio J.; Qin, Chuanjiang; Adachi, Chihaya; Qi, YabingJournal of Physical Chemistry Letters (2017), 8 (14), 3193-3198CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Organo-Pb-halide perovskites are promising materials for optoelectronic applications. Perovskite solar cells have reached power conversion efficiencies of >22%, and perovskite light-emitting diodes (LEDs) have recently achieved >11% external quantum efficiency. To date, most research on perovskite LEDs has focused on soln.-processed films. There are many advantages of a vapor-based growth process to prep. perovskites, including ease of patterning, ability to batch process, and material compatibility. An all-vapor perovskite growth process by CVD was studied, and luminance ≤560 cd/m2 was demonstrated.
- 49Juarez-Perez, E. J.; Hawash, Z.; Raga, S. R.; Ono, L. K.; Qi, Y. Thermal Degradation of CH3NH3PbI3 Perovskite into NH3 and CH3I Gases Observed by Coupled Thermogravimetry-Mass Spectrometry Analysis. Energy Environ. Sci. 2016, 9, 3406– 3410, DOI: 10.1039/C6EE02016JGoogle Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVKjtLjM&md5=c6c03d9dbf93e71a54a56d5cf9d7f000Thermal degradation of CH3NH3PbI3 perovskite into NH3 and CH3I gases observed by coupled thermogravimetry-mass spectrometry analysisJuarez-Perez, Emilio J.; Hawash, Zafer; Raga, Sonia R.; Ono, Luis K.; Qi, YabingEnergy & Environmental Science (2016), 9 (11), 3406-3410CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)Thermal gravimetric and DTA (TG-DTA) coupled with quadrupole mass spectrometry (MS) and first principles calcns. were employed to elucidate the chem. nature of released gases during the thermal decompn. of CH3NH3PbI3. In contrast to the common wisdom that CH3NH3PbI3 is decompd. into CH3NH2 and HI, the major gases were methyliodide (CH3I) and ammonia (NH3). We anticipate that our findings will provide new insights into further formulations of the perovskite active material and device design that can prevent methylammonium decompn. and thus increase the long-term stability of perovskite-based optoelectronic devices.
- 50Latini, A.; Gigli, G.; Ciccioli, A. A Study on the Nature of the Thermal Decomposition of Methylammonium Lead Iodide Perovskite CH3NH3PbI3: An attempt to Rationalise Contradictory Experimental Results. Sustainable Energy Fuels 2017, 1, 1351, DOI: 10.1039/C7SE00114BGoogle Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1CrsLrL&md5=c942e4c428cd439c6f0d65b304522ea2A study on the nature of the thermal decomposition of methylammonium lead iodide perovskite, CH3NH3PbI3: an attempt to rationalise contradictory experimental resultsLatini, Alessandro; Gigli, Guido; Ciccioli, AndreaSustainable Energy & Fuels (2017), 1 (6), 1351-1357CODEN: SEFUA7; ISSN:2398-4902. (Royal Society of Chemistry)The nature of the gas phase product released during the thermal decompn. of CH3NH3PbI3 (methylammonium lead iodide) to PbI2 (lead diiodide) under vacuum is discussed on the basis of thermodn. predictions, recently published exptl. results, and new expts. presented here. From the limited data currently available, the nature of the main decompn. path is not clear because, both, the process releasing HI(g) + CH3NH2(g) and that leading to NH3(g) + CH3I(g) were obsd. under different conditions. Our thermodn. anal. showed that process is largely favored for all the CH3NH3PbX3 (X = Cl, Br, I) compds. However, Knudsen effusion mass spectrometry expts. (temp. range 140-240 °C) showed that HI(g) and CH3NH2(g) were the predominant species in the vapor, with process occurring to a much smaller extent than suggested by the thermodn. driving force, thus being of minor importance under effusion conditions. We also found that this process was comparatively enhanced by high temps. and low effusion rates (high impedance orifice). Our exptl. evidence suggested that the thermodynamically favored process was affected by a significant kinetic hindrance. Overall, the prevailing decompn. path is likely to markedly depend on the actual operative conditions.
- 51Deretzis, I.; Alberti, A.; Pellegrino, G.; Smecca, E.; Giannazzo, F.; Sakai, N.; Miyasaka, T.; LaMagna, A. Atomistic Origins of CH3NH3PbI3 degradation to PbI2 in vacuum. Appl. Phys. Lett. 2015, 106, 131904, DOI: 10.1063/1.4916821Google Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlslCntLs%253D&md5=6e80b96477b15ae873f7a2926a0337efAtomistic origins of CH3NH3PbI3 degradation to PbI2 in vacuumDeretzis, I.; Alberti, A.; Pellegrino, G.; Smecca, E.; Giannazzo, F.; Sakai, N.; Miyasaka, T.; La Magna, A.Applied Physics Letters (2015), 106 (13), 131904/1-131904/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)We study the mechanisms of CH3NH3PbI3 degrdn. and its transformation to PbI2 by means of X-ray diffraction and the d. functional theory. The exptl. anal. shows that the material can degrade in both air and vacuum conditions, with humidity and temp.-annealing strongly accelerating such process. Based on ab initio calcns., we argue that even in the absence of humidity, a decompn. of the perovskite structure can take place through the statistical formation of mol. defects with a non-ionic character, whose volatility at surfaces should break the thermodn. defect equil. We finally discuss the strategies that can limit such phenomenon and subsequently prolong the lifetime of the material. (c) 2015 American Institute of Physics.
- 52Stoumpos, C. C.; Malliakas, C. D.; Kanatzidis, M. G. Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties. Inorg. Chem. 2013, 52, 9019– 9038, DOI: 10.1021/ic401215xGoogle Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtVGqsL3N&md5=94c35d645dcd9770b4097d0bd440269bSemiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent PropertiesStoumpos, Constantinos C.; Malliakas, Christos D.; Kanatzidis, Mercouri G.Inorganic Chemistry (2013), 52 (15), 9019-9038CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)A broad org.-inorg. series of hybrid metal iodide perovskites AMI3, where A is the methylammonium (MeNH3+) or formamidinium (HC(NH2)2+) cation and M is Sn (1 and 2) or Pb (3 and 4) are reported. The compds. were prepd. through a variety of synthetic approaches, and the nature of the resulting materials is discussed in terms of their thermal stability and optical and electronic properties. The chem. and phys. properties of these materials strongly depend on the prepn. method. Single crystal x-ray diffraction anal. of 1-4 classifies the compds. in the perovskite structural family. Structural phase transitions were obsd. and studied by temp.-dependent single crystal x-ray diffraction in the 100-400 K range. The charge transport properties of the materials are discussed in conjunction with diffuse reflectance studies in the mid-IR region that display characteristic absorption features. Temp.-dependent studies show a strong dependence of the resistivity as a function of the crystal structure. Optical absorption measurements indicate that 1-4 behave as direct-gap semiconductors with energy band gaps distributed at 1.25-1.75 eV. The compds. exhibit an intense near-IR luminescence (PL) emission in the 700-1000 nm range (1.1-1.7 eV) at room temp. Solid solns. between the Sn and Pb compds. are readily accessible throughout the compn. range. The optical properties such as energy band gap, emission intensity, and wavelength can be readily controlled for the isostructural series of solid solns. MeNH3Sn1-xPbxI3 (5). The charge transport type in these materials was characterized by Seebeck coeff. and Hall-effect measurements. The compds. behave as p- or n-type semiconductors depending on the prepn. method. The samples with the lowest carrier concn. are prepd. from soln. and are n-type; p-type samples can be obtained through solid state reactions exposed in air in a controllable manner. In the case of Sn compds., there is a facile tendency toward oxidn. which causes the materials to be doped with Sn4+ and thus behave as p-type semiconductors displaying metal-like cond. The compds. appear to possess very high estd. electron and hole mobilities that exceed 2000 cm2/(V s) and 300 cm2/(V s), resp., as shown in the case of MeNH3SnI3 (1). The authors also compare the properties of the title hybrid materials with those of the all-inorg. CsSnI3 and CsPbI3 prepd. using identical synthetic methods.
- 53Dimesso, L.; Dimamay, M.; Hamburger, M.; Jaegermann, W. Properties of CH3NH3PbX3 (X = I, Br, Cl) Powders as Precursors for Organic/Inorganic Solar Cells. Chem. Mater. 2014, 26, 6762– 6770, DOI: 10.1021/cm503240kGoogle Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvFaqu7bF&md5=a2e05a7682d381a74647fa66b7909c45Properties of CH3NH3PbX3 (X = I, Br, Cl) Powders as Precursors for Organic/Inorganic Solar CellsDimesso, L.; Dimamay, M.; Hamburger, M.; Jaegermann, W.Chemistry of Materials (2014), 26 (23), 6762-6770CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The MeNH3PbX3 (X = Cl, Br, I) perovskites were prepd. by a self-organization processes using different precursor solns. The XRD anal. indicates the formation, at room temp., of a tetragonal structure (space group I4/mcm) for X = I, of a cubic structure (space group Pm‾3m) for X = Br, and of centro-sym. cubic structure (space group Pm3m) for X = Cl, resp. The structural anal. revealed the formation of MeNH3Cl as secondary phase in the Cl-contg. system. The morphol. study revealed the formation of rhombo-hexagonal dodecahedra crystallite for X = I, Br, whereas cube-like aggregates were obsd. for X = Cl. The TGA performed in air did not reveal any loss until 250° for X = I and 300° for X = Br, resp., whereas the DTA detected 2 endothermic thermal events (at 336 and 409°) for X = I and one only (379°) for X = Br, resp. The IR spectra (IR) of the powders conformed to the 3-fold symmetry of the methylammonium ion which rotates around the C-N axis. Optical absorption measurements indicated that the MeNH3PbX3 systems behave as direct-gap semiconductors with energy band gaps of 1.53 eV for X = I, 2.20 eV for X = Br, and 3.00 eV for X = Cl, resp., at room temp. The direct-gap semicond. for X = I and X = Br was confirmed by the photoluminescence emission measurements, whereas the compd. for X = Cl is inactive. Iodine-contg. powders were dissolved in an org. solvent (dimethyl-formamide, DMF). The dispersion (100-300 μL) was dropped on glassy substrates on which thick films were obtained by spin-coating and thermal treatment at 120° for ∼5 min. The prepn. of the layers was performed in air at room temp.
- 54Nenon, D. P.; Christians, J. A.; Wheeler, L. M.; Blackburn, J. L.; Sanehira, E. M.; Dou, B.; Olsen, M. L.; Zhu, K.; Berry, J. J.; Luther, J. M. Structural and Chemical Evolution of Methylammonium Lead Halide Perovskites During Thermal Processing from Solution. Energy Environ. Sci. 2016, 9, 2072– 2082, DOI: 10.1039/C6EE01047DGoogle Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmvFylurk%253D&md5=c9bcf86e4e67ed408c5a0516ad3ba84eStructural and chemical evolution of methylammonium lead halide perovskites during thermal processing from solutionNenon, David P.; Christians, Jeffrey A.; Wheeler, Lance M.; Blackburn, Jeffrey L.; Sanehira, Erin M.; Dou, Benjia; Olsen, Michele L.; Zhu, Kai; Berry, Joseph J.; Luther, Joseph M.Energy & Environmental Science (2016), 9 (6), 2072-2082CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)Following the prominent success of CH3NH3PbI3 in photovoltaics and other optoelectronic applications, focus has been placed on better understanding perovskite crystn. from precursor and intermediate phases in order to facilitate improved crystallinity often desirable for advancing optoelectronic properties. Understanding of stability and degrdn. is also of crit. importance as these materials seek com. applications. In this study, we investigate the evolution of perovskites formed from targeted precursor chemistries by correlating in situ temp.-dependent X-ray diffraction, thermogravimetric anal., and mass spectral anal. of the evolved species. This suite of analyses reveals important precursor compn.-induced variations in the processes underpinning perovskite formation and degrdn. The addn. of Cl- leads to widely different precursor evolution and perovskite formation kinetics, and results in significant changes to the degrdn. mechanism, including suppression of cryst. PbI2 formation and modification of the thermal stability of the perovskite phase. This work highlights the role of perovskite precursor chem. in both its formation and degrdn.
- 55Kottokkaran, R.; Abbas, H.; Balaji, G.; Zhang, L.; Samiee, M.; Kitahara, A.; Noack, M.; Dalal, V. Highly Reproducible Vapor Deposition Technique, Device Physics and Structural Instability of Perovskite Solar Cells. IEEE 42nd Photovoltaic Specialist Conference (PVSC) 2015, 42, 1– 4, DOI: 10.1109/PVSC.2015.7355612Google ScholarThere is no corresponding record for this reference.
- 56Williams, A. E.; Holliman, P. J.; Carnie, M. J.; Davies, M. L.; Worsley, D. A.; Watson, T. M. Perovskite Processing for Photovoltaics: A Spectrothermal Evaluation. J. Mater. Chem. A 2014, 2, 19338– 19346, DOI: 10.1039/C4TA04725GGoogle Scholar56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslaisrjJ&md5=5e7ba07965dcce4306da59652e02eeedPerovskite processing for photovoltaics: a spectro-thermal evaluationWilliams, Alice E.; Holliman, Peter J.; Carnie, Matthew J.; Davies, Matthew L.; Worsley, David A.; Watson, Trystan M.Journal of Materials Chemistry A: Materials for Energy and Sustainability (2014), 2 (45), 19338-19346CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)Thermal anal. (TGA and DSC), coupled with evolved gas FTIR spectroscopy, has been used to study the changes occurring during, and differences between materials after, the annealing step of mixed-halide methylammonium lead halide perovskites. This is important because, to date, the material is the most efficient light harvester in highly efficient, 3rd generation perovskite photovoltaic devices, and processing plays a significant role in device performance. TGA-FTIR data show only solvent evolution during the annealing step, while post-annealing anal. shows that the resulting material still contains a significant amt. of residual solvent; however, efficient DMF removal was possible using a silica gel desiccant for a period of 3 days. The data also show that methylammonium halide decompn. does not occur until temps. are well above those used for perovskite processing, suggesting that this is not a significant issue for device manuf. The absence of a well-defined, reversible tetragonal-cubic phase change around 55° in the DSC data of the annealed material, and the presence of HCl in evolved gas analyzed following thermal decompn., demonstrates that CH3NH3I3-xClx does retain some Cl after annealing and does not simply form stoichiometric CH3NH3PbI3 as has been suggested by some workers.
- 57Showman, A. P. Hydrogen Halides on Jupiter and Saturn. Icarus 2001, 152, 140– 150, DOI: 10.1006/icar.2001.6614Google ScholarThere is no corresponding record for this reference.
- 58Jay, A. N.; Daniel, K. A.; Patterson, E. V. Atom-Centered Density Matrix Propagation Calculations on the Methyl Transfer from CH3Cl to NH3: Gas-Phase and Continuum-Solvated Trajectories. J. Chem. Theory Comput. 2007, 3, 336– 343, DOI: 10.1021/ct6002803Google Scholar58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXnvVegtQ%253D%253D&md5=5b0000151f50ce6a49fb727c2e2951bcAtom-Centered Density Matrix Propagation Calculations on the Methyl Transfer from CH3Cl to NH3: Gas-Phase and Continuum-Solvated TrajectoriesJay, Ashley N.; Daniel, Kelly A.; Patterson, Eric V.Journal of Chemical Theory and Computation (2007), 3 (2), 336-343CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)Atom-centered d. matrix propagation (ADMP) calcns. have been carried out to det. gas-phase and continuum-solvated (aq.) trajectories for the Menshutkin reaction of Me chloride with ammonia. The gas-phase trajectories reveal an exit channel that has not been previously reported. The aq. trajectories give the expected results, indicating that solvated ADMP trajectories may be successfully computed using implicit solvation models. The solvated trajectories demonstrate the same stability and convergence qualities as the gas-phase trajectories.
- 59Patterson, E. V. Private communication.Google ScholarThere is no corresponding record for this reference.
- 60
Note that, while the derivation of total pressure from KEML measurements requires the gas phase composition to be known, assuming the occurrence of processes 8, 9, or 10 has a very small effect on the calculated pressure, because the relevant average molecular mass of the vapor phase is very similar in all three cases (see ref (27)).
There is no corresponding record for this reference. - 61Łubkowski, J.; Błażejowski, J. Thermal Properties and Thermochemistry of Alkanaminium Bromides. Thermochim. Acta 1990, 157, 259– 277, DOI: 10.1016/0040-6031(90)80027-VGoogle Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXktlektrs%253D&md5=d0b732d1794097e06c9a5469a8a43f93Thermal properties and thermochemistry of alkanaminium bromidesLubkowski, Jacek; Blazejowski, JerzyThermochimica Acta (1990), 157 (2), 259-77CODEN: THACAS; ISSN:0040-6031.The thermal behavior of [(CnH2n+1)pNH4-p]Br (n = 0-4 and p = 1-4) was studied by thermoanal. methods (DTA, TG and DTG). All the compds. examd. undergo decompn. upon heating, leading to their total volatilization. In the case of primary, secondary and tertiary amine hydrobromides, the thermal-dissocn. process is accompanied by the release of the appropriate amines and HBr to the gaseous phase. Thermogravimetric curves for these derivs. indicate that the process comprises 2 stages. In both steps thermal dissocn. proceeds via the same chem. mechanism; however, each step is detd. by different kinetics. Quaternary salts decomp. in only 1 step which is accompanied by the release of the appropriate tertiary amines and bromoalkanes to the gaseous phase. The latter process requires that the remarkable activation barrier to be overcome in addn. to that resulting from the thermodn. requirements. On the other hand, the dissociative volatilization of the former derivs. proceeds essentially without any addnl. barrier over that imposed by the enthalpy change for the reaction. The enthalpies of the thermal dissocn. of hydrobromides were evaluated from the nonisothermal thermogravimetric curves, and these values, together with the thermochem. data available in the literature, were used to evaluate the enthalpies of formation and the crystal-lattice energies of the compds. The crystal-lattice energy was also examd. within the Kapustinskii-Yatsimirskii approach, which assumes an additive character of this quantity. The essential thermal and thermochem. characteristics, as well as the influence of the structure of amines on the thermal behavior of alkanaminium bromides are also reviewed and discussed.
- 62Dokurno, P.; Łubkowski, J.; Błażejowski, J. Thermal Properties, Thermolysis and Thermochemistry of Alkanaminium Iodides. Thermochim. Acta 1990, 165, 31– 48, DOI: 10.1016/0040-6031(90)80204-CGoogle Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXktFylug%253D%253D&md5=64fce80623f09f1da208cd3b667379ceThermal properties, thermolysis and thermochemistry of alkanaminium iodidesDokurno, Pawel; Lubkowski, Jacek; Blazejowski, JerzyThermochimica Acta (1990), 165 (1), 31-48CODEN: THACAS; ISSN:0040-6031.The thermal features of unbranched compds. of general formula [(CnH2n+1)pNH4-p]I, with n = 0-4 and p = 1-4, were studied by thermoanal. methods (DTA, TG, DTG, and Q-TG). All the compds. studied undergo decompn. upon heating, leading to their total volatilization. In the primary step of the thermal dissocn. of these derivs., HI or RI, in the case of quaternary salts, and the appropriate amines are released in the gaseous phase. This simple thermal decompn. pattern is usually complicated by secondary reactions of an oxidative nature. The latter processes most probably originate from the thermal instability of HI, which can spontaneously decomp. to H2 and I2 giving iodine mols. of high oxidative potential. The enthalpies of the thermal dissocn. were estd. on the basis of the van't Hoff equation using dynamic thermogravimetric curves. Values derived in this way were used together with available literature data to evaluate the enthalpies of formation and the crystal lattice energies of the hydriodides studied. The crystal lattice energy problems were also examd. within the Kapustinskii-Yatsimirskii approach. An attempt was made to describe the kinetics of the thermal decompn. by adopting an Arrhenius model. The influence of the structure of the amines on the thermal behavior of their iodide salts is reviewed and thoroughly discussed.
- 63Sawicka, M.; Storoniak, P.; Skurski, P.; Błażejowski, J.; Rak, J. TG-FTIR, DSC and Quantum Chemical Studies of the Thermal Decomposition of Quaternary Methylammonium Halides. Chem. Phys. 2006, 324, 425– 437, DOI: 10.1016/j.chemphys.2005.11.023Google Scholar63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XkvFKqt7o%253D&md5=376529aa3bc9877200dc120f42ba4f39TG-FTIR, DSC and quantum chemical studies of the thermal decomposition of quaternary methylammonium halidesSawicka, Marlena; Storoniak, Piotr; Skurski, Piotr; Blazejowski, Jerzy; Rak, JanuszChemical Physics (2006), 324 (2-3), 425-437CODEN: CMPHC2; ISSN:0301-0104. (Elsevier B.V.)The thermal decompn. of quaternary methylammonium halides was studied using thermogravimetry coupled to FTIR (TG-FTIR) and differential scanning calorimetry (DSC) as well as the DFT, MP2, and G2 quantum chem. methods. There is almost perfect agreement between the exptl. IR spectra and those predicted at the B3LYP/6-311G(d,p) level: this has demonstrated for the first time that an equimolar mixt. of trimethylamine and a Me halide is produced as a result of decompn. The exptl. enthalpies of dissocn. are 153.4, 171.2, and 186.7 kJ/mol for chloride, bromide, and iodide, resp.; values that correlate well with the calcd. enthalpies of dissocn. based on crystal lattice energies and quantum chem. thermodn. barriers. The exptl. activation barriers estd. from the least-squares fit of the F1 kinetic model (first-order process) to thermogravimetric traces - 283, 244 and 204 kJ/mol for chloride, bromide, and iodide, resp. - agree very well with theor. calcd. values. The theor. approach assumed in this work has been shown capable of predicting the relevant characteristics of the thermal decompn. of solids with exptl. accuracy.
- 64Dong, C.; Song, X.; Meijer, E. J.; Chen, G.; Xu, Y.; Yu, J. Mechanism Studies on Thermal Dissociation of tri-n-octylamine hydrochloride with FTIR, TG, DSC and quantum chemical methods. J. Chem. Sci. 2017, 129, 1431– 1440, DOI: 10.1007/s12039-017-1357-4Google Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVCrtrvP&md5=630cf0f8ea8df562a5e3bc307fd092daMechanism studies on thermal dissociation of tri-n-octylamine hydrochloride with FTIR, TG, DSC and quantum chemical methodsDong, Chunhua; Song, Xingfu; Meijer, Evert Jan; Chen, Guilan; Xu, Yanxia; Yu, JianguoJournal of Chemical Sciences (Berlin, Germany) (2017), 129 (9), 1431-1440CODEN: JCSBB5; ISSN:0974-3626. (Springer GmbH)The thermal dissocn. of tri-n-octylamine hydrochloride was investigated using both the quantum chem. simulation and exptl. methods. The pathway through which a mixt. of tri-n-octylamine and hydrogen chloride, rather than di-n-octylamine and 1-chlorooctane, are produced has been detd. through transition state search with intrinsic reaction coordinate calcns. Particularly, strong agreement between the exptl. FTIR spectra and that of TOA demonstrates the same result for the first time. Moreover, the thermal dissocn. of TOAHCl proceeds in two continuous steps, which is different from the low mol. mass amine hydrochlorides. The exptl. enthalpy of the dissocn. was 70.793 kJmol-1 with DSC measurement which is very close to the d. functional theory calcn. result 69.395 kJmol-1. Furthermore, with the aid of DFT calcns., some other important thermochem. characteristics such as crystal lattice energy with the value of 510.597 kJmol-1 were evaluated by means of Born-Fajans-Haber cycle.
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Abstract
Figure 1
Figure 1. Enthalpy and entropy level scheme for possible formation/decomposition processes of CH3NH3PbX3 perovskites. Decomposition to precursors can be both endothermic and exothermic. The minor process leading to the formation of CH3NH3X(g) (see Figure 3) is not shown. Enthalpy levels are not to scale.
Figure 2
Figure 2. Stability order of CH3NH3PbX3 for X = Cl,Br,I with respect to different processes.
Figure 3
Figure 4
Figure 5
References
This article references 65 other publications.
- 1Asghar, M. I.; Zhang, J.; Wang, H.; Lund, P. D. Device Stability of perovskite Solar Cells: A review. Renewable Sustainable Energy Rev. 2017, 77, 131– 146, DOI: 10.1016/j.rser.2017.04.0031https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlvVOisbY%253D&md5=3c258ad2d58d9aa3609cdd636c97c6a8Device stability of perovskite solar cells - A reviewAsghar, M. I.; Zhang, J.; Wang, H.; Lund, P. D.Renewable & Sustainable Energy Reviews (2017), 77 (), 131-146CODEN: RSERFH; ISSN:1364-0321. (Elsevier Ltd.)A review. This work provides a thorough overview of state of the art of stability of perovskite solar cells (PSCs) and covers important degrdn. issues involved in this technol. Degrdn. factors, which are reported in the literature affecting the stability of PSCs, are discussed. Several degrdn. mechanisms resulting from thermal and chem. instabilities, phase transformations, exposure to visible and UV light, moisture and oxygen and most importantly sealing issues are thoroughly analyzed. Methods are suggested to study most of these degrdn. mechanisms in a systematic way. In addn., environmental assessment of PSCs is briefly covered. Alternative materials and their prepn. methods are screened with respect to stability of the device. Overall, this work contributes in developing better understanding of the degrdn. mechanisms and help in improving overall stability of the PSCs.
- 2Berhe, T. A.; Su, W.-N.; Chen, C.-H.; Pan, C.-J.; Cheng, J.-H.; Chen, H.-M.; Tsai, M.-C.; Chen, L.-Y.; Dubale, A. A.; Hwang, B.-J. Organometal Halide Perovskite Solar Cells: Degradation and Staility. Energy Environ. Sci. 2016, 9, 323– 356, DOI: 10.1039/C5EE02733KThere is no corresponding record for this reference.
- 3Manser, J. S.; Saidaminov, M. I.; Christians, J. A.; Bakr, O. M.; Kamat, P. V. Making and Breaking of Lead Halide Perovskites. Acc. Chem. Res. 2016, 49, 330– 338, DOI: 10.1021/acs.accounts.5b004553https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVyhsbc%253D&md5=da6db8049c1c2ef7e9e38e91ad064b6aMaking and Breaking of Lead Halide PerovskitesManser, Joseph S.; Saidaminov, Makhsud I.; Christians, Jeffrey A.; Bakr, Osman M.; Kamat, Prashant V.Accounts of Chemical Research (2016), 49 (2), 330-338CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review. A new front-runner has emerged in the field of next-generation photovoltaics. A unique class of materials, known as org. metal halide perovskites, bridges the gap between low-cost fabrication and exceptional device performance. These compds. can be processed at low temp. (typically in the range 80-150°) and readily self-assemble from the soln. phase into high-quality semiconductor thin films. The low energetic barrier for crystal formation has mixed consequences. On one hand, it enables inexpensive processing and both optical and electronic tunability. The caveat, however, is that many as-formed lead halide perovskite thin films lack chem. and structural stability, undergoing rapid degrdn. in the presence of moisture or heat. To date, improvements in perovskite solar cell efficiency have resulted primarily from better control over thin film morphol., manipulation of the stoichiometry and chem. of lead halide and alkylammonium halide precursors, and the choice of solvent treatment. Proper characterization and tuning of processing parameters can aid in rational optimization of perovskite devices. Likewise, gaining a comprehensive understanding of the degrdn. mechanism and identifying components of the perovskite structure that may be particularly susceptible to attack by moisture are vital to mitigate device degrdn. under operating conditions. This account provides insight into the life cycle of org.-inorg. lead halide perovskites, including (i) the nature of the precursor soln., (ii) formation of solid-state perovskite thin films and single crystals, and (iii) transformation of perovskites into hydrated phases upon exposure to moisture. In particular, spectroscopic and structural characterization techniques shed light on the thermally driven evolution of the perovskite structure. By tuning precursor stoichiometry and chem., and thus the lead halide charge-transfer complexes present in soln., crystn. kinetics can be tailored to yield improved thin film homogeneity. Because degrdn. of the as-formed perovskite film is in many ways analogous to its initial formation, the same suite of monitoring techniques reveals the moisture-induced transformation of low band gap methylammonium lead iodide (CH3NH3PbI3) to wide band gap hydrate compds. The rate of degrdn. is increased upon exposure to light. Interestingly, the hydration process is reversible under certain conditions. This facile formation and subsequent chem. lability raises the question of whether CH3NH3PbI3 and its analogs are thermodynamically stable phases, thus posing a significant challenge to the development of transformative perovskite photovoltaics. Adequately addressing issues of structural and chem. stability under real-world operating conditions is paramount if perovskite solar cells are to make an impact beyond the bench top. Expanding our fundamental knowledge of lead halide perovskite formation and degrdn. pathways can facilitate fabrication of stable, high-quality perovskite thin films for the next generation of photovoltaic and light emitting devices.
- 4Wang, D.; Wright, M.; Elumalai, N. K.; Uddin, A. Stability of perovskite Solar Cells. Solar Energy Mater. Sol. Energy Mater. Sol. Cells 2016, 147, 255– 275, DOI: 10.1016/j.solmat.2015.12.0254https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlygtQ%253D%253D&md5=bbeb0a2e8c23923fcd88960e5a92dd92Stability of perovskite solar cellsWang, Dian; Wright, Matthew; Elumalai, Naveen Kumar; Uddin, AshrafSolar Energy Materials & Solar Cells (2016), 147 (), 255-275CODEN: SEMCEQ; ISSN:0927-0248. (Elsevier B.V.)The performance of perovskite solar cells has increased at an unprecedented rate, with efficiencies currently exceeding 20%. This technol. is particularly promising, as it is compatible with cheap soln. processing. For a thin-film solar product to be com. viable, it must pass the IEC 61646 testing stds., regarding the environmental stability. Currently, the poor stability of perovskite solar cells is a barrier to commercialization. The main issue causing this problem is the instability of the perovskite layer when in contact with moisture; however, it is important to explore stability problems with the other layers and interfaces within the device. The stability issues discussed in this review highlight the need to view the device as a whole system, due to the interdependent relationships between the layers, including: the perovskite absorber, electron transport layers, hole transport layers, other buffer layers and the electrodes. We also discuss other issues pertaining to device stability, such as measurement-induced hysteresis and the requirement for std. testing protocols. For perovskite solar cells to achieve the required stability, future research must focus on improving the intrinsic stability of the perovskite absorber layer, carefully designing the device geometry, and finding durable encapsulant materials, which seal the device from moisture.
- 5Leijtens, T.; Eperon, G. E.; Noel, N. K.; Habisreutinger, S. N.; Petrozza, A.; Snaith, H. J. Stability of Metal Halide Perovskite Solar Cells. Adv. Energy Mater. 2015, 5, 1500963, DOI: 10.1002/aenm.201500963There is no corresponding record for this reference.
- 6Niu, G.; Guo, X.; Wang, L. Review of Recent Progress in Chemical Stability of Perovskite Solar Cells. J. Mater. Chem. A 2015, 3, 8970– 8980, DOI: 10.1039/C4TA04994B6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitVaqur%252FN&md5=1d6428e608a087ab03a54eb6d885c578Review of recent progress in chemical stability of perovskite solar cellsNiu, Guangda; Guo, Xudong; Wang, LiduoJournal of Materials Chemistry A: Materials for Energy and Sustainability (2015), 3 (17), 8970-8980CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)This review summarizes recent studies of the relationship of the chem. stability of perovskite solar cells with their environment (oxygen and moisture, UV light, soln. process, temp.) and corresponding possible solns. In recent years, the record efficiency of perovskite solar cells has been updated from 9.7% to 20.1%. However, there has been very little study of the issue of stability, which restricts the outdoor application of perovskite solar cells. The issues of the degrdn. of perovskite and the stability of perovskite solar cell devices should be urgently addressed to achieve good reproducibility and long lifetimes for perovskite solar cells with high conversion efficiency. Without studies on stability, exciting achievements cannot be transferred from the lab. to industry and outdoor applications. In order to improve their stability, a basic understanding of the degrdn. process of perovskite solar cells in different conditions should be acquired via thorough study.
- 7Ono, L. K.; Juarez-Perez, E. J.; Qi, Y. Progress on Perovskite Materials and Solar Cells with Mixed Cations and Halide Anions. ACS Appl. Mater. Interfaces 2017, 9, 30197– 30246, DOI: 10.1021/acsami.7b060017https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFaqsrjF&md5=4e3694cdf0a38b99b7a33d32d4442d43Progress on Perovskite Materials and Solar Cells with Mixed Cations and Halide AnionsOno, Luis K.; Juarez-Perez, Emilio J.; Qi, YabingACS Applied Materials & Interfaces (2017), 9 (36), 30197-30246CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)A review. Org.-inorg. halide perovskite materials (e.g. MAPbI3, FAPbI3, etc; where MA = CH3NH3+; FA = CH(NH2)2+) have been studied intensively for photovoltaic applications. Major concerns for the commercialization of perovskite photovoltaic technol. to take off include lead toxicity, long-term stability, hysteresis, and optimal bandgap. Therefore, there is still needs for further exploration of alternative candidates. Elemental compn. engineering of MAPbI3 and FAPbI3 has been proposed to address the above concerns. Among the best six certified power conversion efficiencies reported by National Renewable Energy Lab. (NREL) on perovskite-based solar cells, four are based on mixed perovskites (e.g. MAPbI1-xBrx, FA0.85MA0.15PbI2.55Br0.45, Cs0.1FA0.75MA0.15PbI2.49Br0.51). In this article, we review the recent progress on the synthesis and fundamental aspects of mixed cation and halide perovskites correlating with device performance, long-term stability, and hysteresis. In the outlook, we outline the future research directions based on the reported results as well as related topics that warrant further investigation.
- 8Chen, J.; Cai, X.; Yang, D.; Song, D.; Wang, J.; Jiang, J.; Ma, A.; Lv, S.; Hu, M. Z.; Ni, C. Recent Progress in Stabilizing Hybrid Perovskites for Solar Cell Applications. J. Power Sources 2017, 355, 98– 133, DOI: 10.1016/j.jpowsour.2017.04.0258https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmtlKru74%253D&md5=9ebfaeda6b18c49c7f9bf149436d03c1Recent progress in stabilizing hybrid perovskites for solar cell applicationsChen, Jianqing; Cai, Xin; Yang, Donghui; Song, Dan; Wang, Jiajia; Jiang, Jinghua; Ma, Aibin; Lv, Shiquan; Hu, Michael Z.; Ni, ChaoyingJournal of Power Sources (2017), 355 (), 98-133CODEN: JPSODZ; ISSN:0378-7753. (Elsevier B.V.)A review is given. Hybrid inorg.-org. perovskites have quickly evolved as a promising group of materials for solar cells and optoelectronic applications mainly owing to the inexpensive materials, relatively simple and versatile fabrication and high power conversion efficiency (PCE). The certified energy conversion efficiency for perovskite solar cell (PSC) has reached above 20%, which is compatible to the current best for com. applications. However, long-term stabilities of the materials and devices remain to be the biggest challenging issue for realistic implementation of the PSCs. This article discusses the key issues related to the stability of perovskite absorbing layer including crystal structural stability, chem. stability under moisture, oxygen, illumination and interface reaction, effects of electron-transporting materials (ETM), hole-transporting materials (HTM), contact electrodes, ion migration and prepn. conditions. Towards the end, prospective strategies for improving the stability of PSCs are also briefly discussed and summarized. We focus on recent understanding of the stability of materials and devices and our perspectives about the strategies for the stability improvement.
- 9Slavney, A. H.; Smaha, R. W.; Smith, I. C.; Jaffe, A.; Umeyama, D.; Karunadasa, H. I. Chemical Approach to Addressing the Instability and Toxicity of Lead-Halide Perovskite Absorbers. Inorg. Chem. 2017, 56, 46– 55, DOI: 10.1021/acs.inorgchem.6b013369https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1ynsb7P&md5=903889ff9e5b8151fb5828a98de114e0Chemical Approaches to Addressing the Instability and Toxicity of Lead-Halide Perovskite AbsorbersSlavney, Adam H.; Smaha, Rebecca W.; Smith, Ian C.; Jaffe, Adam; Umeyama, Daiki; Karunadasa, Hemamala I.Inorganic Chemistry (2017), 56 (1), 46-55CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)A review. The impressive rise in efficiencies of solar cells employing the three-dimensional (3D) lead-iodide perovskite absorbers APbI3 (A = monovalent cation) has generated intense excitement. Although these perovskites have remarkable properties as solar-cell absorbers, their potential commercialization now requires a greater focus on the materials' inherent shortcomings and environmental impact. This creates a challenge and an opportunity for synthetic chemists to address these issues through the design of new materials. Synthetic chem. offers powerful tools for manipulating the magnificent flexibility of the perovskite lattice to expand the no. of functional analogs to APbI3. To highlight improvements that should be targeted in new materials, here we discuss the intrinsic instability and toxicity of 3D lead-halide perovskites. We consider possible sources of these instabilities and propose methods to overcome them through synthetic design. We also discuss new materials developed for realizing the exceptional photophys. properties of lead-halide perovskites in more environmentally benign materials. In this Forum Article, we provide a brief overview of the field with a focus on our group's contributions to identifying and addressing problems inherent to 3D lead-halide perovskites.
- 10Ito, S.; Tanaka, S.; Manabe, K.; Nishino, H. Effects of Surface Blocking Layer of Sb2S3 on Nanocrystalline TiO2 for CH3NH3PbI3 Perovskite Solar Cells. J. Phys. Chem. C 2014, 118, 16995– 17000, DOI: 10.1021/jp500449z10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXnt1amt7s%253D&md5=0b3efa8bca57ca6bf95ccefc79178b9aEffects of Surface Blocking Layer of Sb2S3 on Nanocrystalline TiO2 for CH3NH3PbI3 Perovskite Solar CellsIto, Seigo; Tanaka, Soichiro; Manabe, Kyohei; Nishino, HitoshiJournal of Physical Chemistry C (2014), 118 (30), 16995-17000CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Sb2S3 layers were inserted at the interface between TiO2 and CH3NH3PbI3 perovskite to create CH3NH3PbI3 solar cells using inorg. hole transporting material (CuSCN). The CH3NH3PbI3 layer was spin-coated by a one-drop method onto the nanocryst. TiO2 layer. The photoenergy conversion efficiencies were improved with Sb2S3 layers (the best efficiency: 5.24%). During the light exposure test without encapsulation, the CH3NH3PbI3 solar cells without Sb2S3 deteriorated to zero efficiency in 12 h and were completely changed from black to yellow because the perovskite CH3NH3PbI3 was changed to hexagonal PbI2. With Sb2S3, on the other hand, the CH3NH3PbI3 solar cells became stable against light exposure without encapsulation, which did not change the crystal structure or the wavelength edges of absorption and IPCE. Therefore, it was believed that degrdn. can occur at the interface between TiO2 and CH3NH3PbI3.
- 11Matteocci, F.; Cinà, L.; Lamanna, E.; Cacovich, S.; Divitini, G.; Midgley, P. A.; Ducati, C.; Di Carlo, A. Encapsulation for Long-Term Stability Enhancement of Perovskite Solar Cells. Nano Energy 2016, 30, 162– 172, DOI: 10.1016/j.nanoen.2016.09.04111https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslWju73L&md5=775f04e1de37781f8eb65a12a288fd05Encapsulation for long-term stability enhancement of perovskite solar cellsMatteocci, Fabio; Cina, Lucio; Lamanna, Enrico; Cacovich, Stefania; Divitini, Giorgio; Midgley, Paul A.; Ducati, Caterina; Di Carlo, AldoNano Energy (2016), 30 (), 162-172CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)Perovskite Solar Cells (PSCs) have achieved power conversion efficiencies (PCEs) comparable to established technologies, but their stability in real-life working conditions - including exposure to moisture, heat and light - has still not been decisively demonstrated. Encapsulation of the cells is vital for increasing device lifetime, as well as shedding light on the intrinsic degrdn. process of the active layers. Here we compare different sealing protocols applied to large area cells (1 cm2, av. PCE 13.6%) to sep. the extrinsic degrdn., due to the external environment, from the intrinsic one, due to the materials themselves. Sealing methods were tested against accelerated life-time tests - damp-heating, prolonged heating and light-soaking. We thus developed and tested a novel sealing procedure that makes PSCs able to maintain a stabilized 10% PCE after heat, light and moisture stress.
- 12Huang, J.; Tan, S.; Lund, P. D.; Zhou, H. Impact of H2O on Organic-Inorganic Hybrid Perovskite Solar Cells. Energy Environ. Sci. 2017, 10, 2284– 2311, DOI: 10.1039/C7EE01674C12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFeqtrnL&md5=bdb1266b10f2a2d08ab9d54fa614b539Impact of H2O on organic-inorganic hybrid perovskite solar cellsHuang, Jianbing; Tan, Shunquan; Lund, Peter D.; Zhou, HuanpingEnergy & Environmental Science (2017), 10 (11), 2284-2311CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)The performance and stability of org.-inorg. hybrid perovskite solar cells (PSCs) is sensitive to water and moisture in an ambient environment. Understanding how H2O influences the perovskite material is also important for developing appropriate control strategies to mitigate the problem. Here we provide a comprehensive review on the effect of water on the state-of-the-art lead-based perovskite solar cells in terms of perovskite material design, perovskite film prepn., device fabrication, and photovoltaic application. It is found that a moderate amt. of water can facilitate nucleation and crystn. of the perovskite material, resulting in better perovskite film quality and enhanced PSC performance. The perovskite materials are irreversibly destroyed by H2O after a certain level of water, but they exihibit better tolerance than initially expected. Humidity resistant fabrication of high-performance PSC devices and modules should therefore be favored. Generally, water shows a neg. effect on the long-term stability and lifetime of PSCs. To reduce the effects from water during outdoor operation, attention should be paid to different protection methods such as varying the perovskite compn., optimizing the electron/hole transport layer and encapsulation of the device.
- 13Matsumoto, F.; Vorpahl, S. M.; Banks, J. Q.; Sengupta, E.; Ginger, D. S. Photodecomposition and Morphology Evolution of Organometal Halide Perovskite Solar Cells. J. Phys. Chem. C 2015, 119, 20810– 20816, DOI: 10.1021/acs.jpcc.5b0626913https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtlOnur3O&md5=ef1e5d34b19586bbc37df0745a114983Photodecomposition and Morphology Evolution of Organometal Halide Perovskite Solar CellsMatsumoto, Fukashi; Vorpahl, Sarah M.; Banks, Jannel Q.; Sengupta, Esha; Ginger, David S.Journal of Physical Chemistry C (2015), 119 (36), 20810-20816CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)We study the photoinduced degrdn. of hybrid organometal perovskite photovoltaics under illumination and ambient atm. using UV-vis absorption, at. force microscopy, and device performance. We correlate the structural changes in the surface of the perovskite film with changes in the optical and electronic properties of the devices. The photodecompn. of the methylammonium lead triiodide perovskite layer itself proceeds much more slowly than the photodegrdn. of the performance of devices with fullerene/bathocuproine/aluminum top contacts, indicating that the active layer alone is more stable than the interface with the electrodes in this geometry. The evolution of the perovskite active layer performance proceeded through several phases: (1) an initial improvement in device characteristics, (2) a plateau with very slow degrdn., and (3) a catastrophic decline in material performance accompanied by marked changes in film morphol. The rapid increase in surface roughness of the active perovskite semiconductor assocd. with sudden failure also correlates with decreased absorption at the perovskite band edge and growth of a lead iodide absorption feature. We find that degrdn. requires both light and moisture, is accelerated at increased humidity, and scales linearly with light intensity, depending primarily on total photon dose.
- 14Poorkazem, K.; Kelly, T. L. Compositional Engineering to Improve the Stability of Lead Halide Perovskites: A comparative Study of Cationic and Anionic Dopants. ACS Appl. Energy Mater. 2018, 1, 181– 190, DOI: 10.1021/acsaem.7b0006514https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFahsLbE&md5=0b3ae7117b83879d274f773eaaef01c4Compositional Engineering To Improve the Stability of Lead Halide Perovskites: A Comparative Study of Cationic and Anionic DopantsPoorkazem, Kianoosh; Kelly, Timothy L.ACS Applied Energy Materials (2018), 1 (1), 181-190CODEN: AAEMCQ; ISSN:2574-0962. (American Chemical Society)The instability of perovskite solar cells is the single greatest barrier to their commercialization. While a no. of studies have now looked at the effect of perovskite compn. on device stability, many of these have examd. only a single compositional variable. With many of these studies having been carried out under different environmental conditions, and still others lacking environmental controls entirely, it is often difficult to compare the relative effect of various cationic or anionic dopants. To address this knowledge gap, we fabricated CH3NH3PbI3-based solar cells where either the methylammonium or iodide ions were replaced with 20 mol % of a dopant ion (ethylammonium, formamidinium, bromide, or chloride). We then assessed their stability either in a controlled 85% relative humidity environment or under 1 sun illumination in air; both conditions have been previously shown to rapidly decomp. CH3NH3PbI3. Of the dopants studied, the formamidinium cations imparted the best moisture resistance, and the resulting perovskite displayed the lowest photochem. reactivity. We attribute the improved stability of the formamidinium-doped perovskite to the more delocalized pos. charge of the formamidinium cation.
- 15Ono, L. K.; Qi, Y. Surface and Interface Aspects of Organometal Halide Perovskite Materials and Solar Cells. J. Phys. Chem. Lett. 2016, 7, 4764– 4794, DOI: 10.1021/acs.jpclett.6b0195115https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslGhtb7N&md5=2e5620e9175f7bac0fb949d8936225e9Surface and Interface Aspects of Organometal Halide Perovskite Materials and Solar CellsOno, Luis K.; Qi, YabingJournal of Physical Chemistry Letters (2016), 7 (22), 4764-4794CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)A review. The current challenges (e.g., stability, hysteresis, etc.) in organometal halide perovskite solar cell research are closely correlated with surfaces and interfaces. For instance, efficient generation of charges, extn., and transport with min. recombination through interlayer interfaces is crucial to attain high-efficiency solar cell devices. Furthermore, intralayer interfaces may be present in the form of grain boundaries within a film composed of the same material, for example, a polycryst. perovskite layer. The adjacent grains may assume different crystal orientations and/or have different chem. compns., which impacts charge excitation and dynamics and thereby the overall solar cell performance. In this Perspective, we present case studies to demonstrate (1) how surfaces and interfaces can impact material properties and device performance and (2) how these issues can be investigated by surface science techniques, such as scanning probe microscopy, photoelectron spectroscopy, and so forth. We end this Perspective by outlining the future research directions based on the reported results as well as the new trends in the field.
- 16Guerrero, A.; You, J.; Aranda, C.; Kang, Y. O.; Garcia-Belmonte, G.; Zhou, H.; Bisquert, J.; Yang, Y. Interfacial Degradation of Planar Lead Halide Perovskite Solar Cells. ACS Nano 2016, 10, 218– 224, DOI: 10.1021/acsnano.5b0368716https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVeqt7jP&md5=74935f8cf4492ca73428599dcc7a100aInterfacial Degradation of Planar Lead Halide Perovskite Solar CellsGuerrero, Antonio; You, Jingbi; Aranda, Clara; Kang, Yong Soo; Garcia-Belmonte, Germa; Zhou, Huanping; Bisquert, Juan; Yang, YangACS Nano (2016), 10 (1), 218-224CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)The stability of perovskite solar cells is one of the major challenges for this technol. to reach commercialization, with water believed to be the major degrdn. source. In this work, a range of devices contg. different cathode metal contacts in the configuration ITO/PEDOT:PSS/MAPbI3/PCBM/Metal are fully elec. characterized before and after degrdn. caused by steady illumination during 4 h that induces a dramatic redn. in power conversion efficiency from values of 12 to 1.8%. We show that a decrease in performance and generation of the S-shape is assocd. with chem. degrdn. of the metal contact. Alternatively, use of Cr2O3/Cr as the contact enhances the stability, but modification of the energetic profile during steady illumination takes place, significantly reducing the performance. Several techniques including capacitance-voltage, X-ray diffraction, and optical absorption results suggest that the properties of the bulk perovskite layer are little affected in the device degrdn. process. Capacitance-voltage and impedance spectroscopy results show that the elec. properties of the cathode contact are being modified by generation of a dipole at the cathode that causes a large shift of the flat-band potential that modifies the interfacial energy barrier and impedes efficient extn. of electrons. Ionic movement in the perovskite layer changes the energy profile close to the contacts, modifying the energy level stabilization at the cathode. These results provide insights into the degrdn. mechanisms of perovskite solar cells and highlight the importance to further study the use of protecting layers to avoid the chem. reactivity of the perovskite with the external contacts.
- 17Huang, W.; Manser, J. S.; Kamat, P. V.; Ptasinska, S. Evolution of Chemical Composition, Morphology, and Photovoltaic Efficiency of CH3NH3PbI3 Perovskite under Ambient Conditions. Chem. Chem. Mater. 2016, 28, 303– 311, DOI: 10.1021/acs.chemmater.5b04122There is no corresponding record for this reference.
- 18Koocher, N. Z.; Saldana-Greco, D.; Wang, F.; Liu, S.; Rappe, A. M. Polarization Dependenceof Water Adsoprtion to CH3NH3PbI3 (001). J. Phys. Chem. Lett. 2015, 6, 4371– 438, DOI: 10.1021/acs.jpclett.5b0179718https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsF2ltbrF&md5=8365eb296bec95bac0e070840d90d7fdPolarization Dependence of Water Adsorption to CH3NH3PbI3 (001) SurfacesKoocher, Nathan Z.; Saldana-Greco, Diomedes; Wang, Fenggong; Liu, Shi; Rappe, Andrew M.Journal of Physical Chemistry Letters (2015), 6 (21), 4371-4378CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The instability of organometal halide perovskites when in contact with water is a serious challenge to their feasibility as solar cell materials. Although studies of moisture exposure have been conducted, an atomistic understanding of the degrdn. mechanism is required. Toward this goal, we study the interaction of water with the (001) surfaces of CH3NH3PbI3 under low and high water concns. using d. functional theory. We find that water adsorption is heavily influenced by the orientation of the methylammonium cations close to the surface. We demonstrate that, depending on methylammonium orientation, the water mol. can infiltrate into the hollow site of the surface and get trapped. Controlling dipole orientation via poling or interfacial engineering could thus enhance its moisture stability. No direct reaction between the water and methylammonium mols. is seen. Furthermore, calcns. with an implicit solvation model indicate that a higher water concn. may facilitate degrdn. through increased lattice distortion.
- 19Yuan, H.; Debroye, E.; Janssen, K.; Naiki, H.; Steuwe, C.; Lu, G.; Moris, M.; Orgiu, E.; Uji-I, H.; De Schryver, F.; Samorì, P. Degradation of Methylammonium Lead Iodide Perovskite Structures through Light and Electron Beam Driven Ion Migration. J. Phys. Chem. Lett. 2016, 7, 561– 566, DOI: 10.1021/acs.jpclett.5b0282819https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1KmsLY%253D&md5=64250702d30988b4c910d636c1ee2e8eDegradation of Methylammonium Lead Iodide Perovskite Structures through Light and Electron Beam Driven Ion MigrationYuan, Haifeng; Debroye, Elke; Janssen, Kris; Naiki, Hiroyuki; Steuwe, Christian; Lu, Gang; Moris, Michele; Orgiu, Emanuele; Uji-i, Hiroshi; De Schryver, Frans; Samori, Paolo; Hofkens, Johan; Roeffaers, MaartenJournal of Physical Chemistry Letters (2016), 7 (3), 561-566CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Organometal halide perovskites show promising features for cost-effective application in photovoltaics. The material instability remains a major obstacle to broad application because of the poorly understood degrdn. pathways. Here, the authors apply simultaneous luminescence and electron microscopy on perovskites for the 1st time, allowing the authors to monitor in situ morphol. evolution and optical properties upon perovskite degrdn. Morphol., photoluminescence (PL), and cathodoluminescence of perovskite samples evolve differently upon degrdn. driven by electron beam (e-beam) or by light. A transversal elec. current generated by a scanning electron beam leads to dramatic changes in PL and tunes the energy band gaps continuously alongside film thinning. In contrast, light-induced degrdn. results in material decompn. to scattered particles and shows little PL spectral shifts. The differences in degrdn. can be ascribed to different elec. currents that drive ion migration. Also, soln.-processed perovskite cuboids show heterogeneity in stability which is likely related to crystallinity and morphol. The authors' results reveal the essential role of ion migration in perovskite degrdn. and provide potential avenues to rationally enhance the stability of perovskite materials by reducing ion migration while improving morphol. and crystallinity. It is worth noting that even moderate e-beam currents (86 pA) and acceleration voltages (10 kV) readily induce significant perovskite degrdn. and alter their optical properties. Therefore, attention has to be paid while characterizing such materials using SEM or TEM techniques.
- 20Philippe, B.; Park, B.-W.; Lindblad, R.; Oscarsson, J.; Ahmadi, S.; Johansson, E. M.; Rensmo, H. Chemical and Electronic Structure Characterization of Led Halide Perovskite and Stabilityi Behavior under Different Exposures – A Photoelectron Spectroscopy Investigation. Chem. Mater. 2015, 27, 1720– 1731, DOI: 10.1021/acs.chemmater.5b00348There is no corresponding record for this reference.
- 21Akbulatov, A. F.; Luchkin, S. Yu.; Frolova, L. A.; Dremova, N. N.; Gerasimov, K. L.; Zhidkov, I. S.; Anokhin, A. V.; Kurmaev, E. Z.; Stevenson, K. J.; Troshin, P. A. Probing the Intrinsic Thermal and Photochemical Stability of Hybrid and Inorganic Lead Halide Perovskites. J. Phys. Chem. Lett. 2017, 8, 1211– 1218, DOI: 10.1021/acs.jpclett.6b0302621https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjtVajtr0%253D&md5=06614bfefdafc451913bbde716b4e850Probing the Intrinsic Thermal and Photochemical Stability of Hybrid and Inorganic Lead Halide PerovskitesAkbulatov, Azat F.; Luchkin, Sergey Yu.; Frolova, Lyubov A.; Dremova, Nadezhda N.; Gerasimov, Kirill L.; Zhidkov, Ivan S.; Anokhin, Denis V.; Kurmaev, Ernst Z.; Stevenson, Keith J.; Troshin, Pavel A.Journal of Physical Chemistry Letters (2017), 8 (6), 1211-1218CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)We report a systematic study of thermal and photochem. degrdn. of a series of complex haloplumbates APbX3 (X =I, Br) with hybrid org. (A+ =CH3NH3) and inorg. (A+ =Cs+) cations under anoxic conditions (i.e., without exposure to O and moisture by testing in an inert glovebox environment). We show that the most common hybrid materials (e.g., MAPbI3) are intrinsically unstable with respect to the heat- and light-induced stress and, therefore, can hardly sustain the real solar cell operation conditions. On the contrary, the Ca-based all-inorg. complex Pb halides revealed far superior stability and, therefore, provide an impetus for creation of highly efficient and stable perovskite solar cells that can potentially achieve pragmatic operational benchmarks.
- 22Conings, B.; Drijkoningen, J.; Gauquelin, N.; Babayigit, A.; D’Haen, J.; D’Olieslaeger, L.; Ethirajan, A.; Verbeeck, J.; Manca, J.; Mosconi, E.; De Angelis, F.; Boyen, H.-G. Intrinsic Thermal Instability of Methylammonium Lead Trihalide Perovskite. Adv. Energy Mater. 2015, 5, 1500477, DOI: 10.1002/aenm.201500477There is no corresponding record for this reference.
- 23Dualeh, A.; Gao, P.; Seok, S. I.; Nazeeruddin, M. K.; Grätzel, M. Thermal Behavior of Methyilammonium Lead-Trihalide Perovskite Photovoltaic Light Harvester. Chem. Mater. 2014, 26, 6160– 6164, DOI: 10.1021/cm502468kThere is no corresponding record for this reference.
- 24Alberti, A.; Deretzis, I.; Pellegrino, G.; Bongiorno, C.; Smecca, E.; Mannino, G.; Giannazzo, F.; Condorelli, G. G.; Sakai, N.; Miyasaka, T. Similar Structural Dynamics for the Degradation of CH3NH3PbI3 in Air and in Vacuum. ChemPhysChem 2015, 16, 3064– 3071, DOI: 10.1002/cphc.20150037424https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVagtb%252FJ&md5=722011e314b057e4a64802930fd08c94Similar Structural Dynamics for the Degradation of CH3NH3PbI3 in Air and in VacuumAlberti, Alessandra; Deretzis, Ioannis; Pellegrino, Giovanna; Bongiorno, Corrado; Smecca, Emanuele; Mannino, Giovanni; Giannazzo, Filippo; Condorelli, Guglielmo Guido; Sakai, Nobuya; Miyasaka, Tsutomu; Spinella, Corrado; La Magna, AntoninoChemPhysChem (2015), 16 (14), 3064-3071CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)We investigate the degrdn. path of MAPbI3 (MA=methylammonium) films over flat TiO2 substrates at room temp. by means of x-ray diffraction, spectroscopic ellipsometry, XPS, and high-resoln. transmission electron microscopy. The degrdn. dynamics is found to be similar in air and under vacuum conditions, which leads to the conclusion that the occurrence of intrinsic thermodn. mechanisms is not necessarily linked to humidity. The process has an early stage, which drives the starting tetragonal lattice in the direction of a cubic at. arrangement. This early stage is followed by a phase change towards PbI2. We describe how this degrdn. product is structurally coupled with the original MAPbI3 lattice through the orientation of its constituent PbI6 octahedra. Our results suggest a slight octahedral rearrangement after volatilization of HI+CH3NH2 or MAI, with a relatively low energy cost. Our expts. also clarify why reducing the interfaces and internal defects in the perovskite lattice enhances the stability of the material.
- 25Ivanov, I. L.; Steparuk, A. S.; Bolyachkina, M. S.; Tsvetkov, D. S.; Safronov, A. P.; Zuev, A. Yu. Thermodynamics of formation of hybrid perovskite-type methylammonium lead halides. J. Chem. Thermodyn. 2018, 116, 253– 258, DOI: 10.1016/j.jct.2017.09.02625https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFOhtrvO&md5=37b330bec5973df397ee028e95217d75Thermodynamics of formation of hybrid perovskite-type methylammonium lead halidesIvanov, I. L.; Steparuk, A. S.; Bolyachkina, M. S.; Tsvetkov, D. S.; Safronov, A. P.; Zuev, A. Yu.Journal of Chemical Thermodynamics (2018), 116 (), 253-258CODEN: JCTDAF; ISSN:0021-9614. (Elsevier Ltd.)Enthalpies of soln. of hybrid perovskites CH3NH3PbX3 (X = Cl, Br, I) in DMSO were measured using soln. calorimetry. Std. enthalpies and Gibbs free energies of formation of CH3NH3PbX3 (X = Cl, Br, I) hybrid perovskites from halides as well as from elements at 298 K were calcd. on the basis of exptl. data obtained and compared with the data available in literature. Excellent agreement was obtained between the std. Gibbs free energy of decompn. of CH3NH3PbX3 into solid PbX2, gaseous HX and methylamine calcd. on the basis of our data and that evaluated on the basis of vapor pressure measurement results reported by other authors. Entropy contribution was shown to play a major role in the stability of hybrid org.-inorg. perovskites with respect to their decompn. on constituent halides.
- 26Nagabhushana, G. P.; Shivaramaiah, R.; Navrotsky, A. Direct Calorimetric Verification of Thermodynamic Instability of Lead Halide Hybrid Perovskites. Proc. Natl. Acad. Sci. U. S. A. 2016, 113, 7717– 7721, DOI: 10.1073/pnas.160785011326https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFentrzM&md5=b3e3b2e535f04cdd69c9021aa7bb2d5aDirect calorimetric verification of thermodynamic instability of lead halide hybrid perovskitesNagabhushana, G. P.; Shivaramaiah, Radha; Navrotsky, AlexandraProceedings of the National Academy of Sciences of the United States of America (2016), 113 (28), 7717-7721CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Hybrid perovskites, esp. methylammonium lead iodide (MAPbI3), exhibit excellent solar power conversion efficiencies. However, their application is plagued by poor chem. and structural stability. Using direct calorimetric measurement of heats of formation, MAPbI3 is shown to be thermodynamically unstable with respect to decompn. to lead iodide and methylammonium iodide, even in the absence of ambient air or light or heat-induced defects, thus limiting its long-term use in devices. The formation enthalpy from binary halide components becomes less favorable in the order MAPbCl3, MAPbBr3, MAPbI3, with only the chloride having a neg. heat of formation. Optimizing the geometric match of constituents as measured by the Goldschmidt tolerance factor provides a potentially quantifiable thermodn. guide for seeking chem. substitutions to enhance stability.
- 27Brunetti, B.; Cavallo, C.; Ciccioli, A.; Gigli, G.; Latini, A. On the Thermal and Thermodynamic (In)stability of Methylammonium Lead Halide Perovskites. Sci. Rep. 2016, 6, 31896, DOI: 10.1038/srep3189627https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVSrsb7N&md5=531e2461d5fd57c414ad5d9959bbd25cOn the Thermal and Thermodynamic (In)Stability of Methylammonium Lead Halide PerovskitesBrunetti, Bruno; Cavallo, Carmen; Ciccioli, Andrea; Gigli, Guido; Latini, AlessandroScientific Reports (2016), 6 (), 31896CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)The interest of the scientific community on methylammonium lead halide perovskites (MAPbX3, X = Cl, Br, I) for hybrid org.-inorg. solar cells has grown exponentially since the first report in 2009. This fact is clearly justified by the very high efficiencies attainable (reaching 20% in lab scale devices) at a fraction of the cost of conventional photovoltaics. However, many problems must be solved before a market introduction of these devices can be envisaged. Perhaps the most important to be addressed is the lack of information regarding the thermal and thermodn. stability of the materials towards decompn., which are intrinsic properties of them and which can seriously limit or even exclude their use in real devices. In this work we present and discuss the results we obtained using non-ambient X-ray diffraction, Knudsen effusion-mass spectrometry (KEMS) and Knudsen effusion mass loss (KEML) techniques on MAPbCl3, MAPbBr3 and MAPbI3. The measurements demonstrate that all the materials decomp. to the corresponding solid lead (II) halide and gaseous methylamine and hydrogen halide, and the decompn. is well detectable even at moderate temps. (∼60 °C). Our results suggest that these materials may be problematic for long term operation of solar devices.Brunetti, B.; Cavallo, C.; Ciccioli, A.; Gigli, G.; Latini, A. Corrigendum: On the Thermal and Thermodynamic (In)Stability of Methylammonium Lead Halide Perovskites. Sci. Rep 2017, 7, 46867, DOI: 10.1038/srep4686727https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1Cms7fL&md5=f8549c08001b340d933daea262c93f84Corrigendum: On the Thermal and Thermodynamic (In)Stability of Methylammonium Lead Halide PerovskitesBrunetti, Bruno; Cavallo, Carmen; Ciccioli, Andrea; Gigli, Guido; Latini, AlessandroScientific Reports (2017), 7 (), 46867CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)There is no expanded citation for this reference.
- 28Thind, A. S.; Huang, X.; Sun, J.; Mishra, R. First-Principle Prediction of a Stable Hexagonal Phase of CH3NH3PbI3. Chem. Mater. 2017, 29, 6003– 6011, DOI: 10.1021/acs.chemmater.7b01781There is no corresponding record for this reference.
- 29Faghihnasiri, M.; Izadifard, M.; Ghazi, M. E. DFT Study of Mechanical Properties and Stability of Cubic Methylammonium Lead Halide Perovskites (CH3NH3PbX3, X = I, Br, Cl). J. Phys. Chem. C 2017, 121, 27059– 27070, DOI: 10.1021/acs.jpcc.7b0712929https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslyhsrrI&md5=420bd1c0c18850d468a88ee52206899cDFT Study of Mechanical Properties and Stability of Cubic Methylammonium Lead Halide Perovskites (CH3NH3PbX3, X = I, Br, Cl)Faghihnasiri, Mahdi; Izadifard, Morteza; Ghazi, Mohammad EbrahimJournal of Physical Chemistry C (2017), 121 (48), 27059-27070CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)In this study, using the d. functional theory, the mech. properties of methylammonium lead halide perovskites (CH3NH3PbX3, X = I, Br, Cl) were investigated. Young's modulus, bulk modulus, and shear modulus, Poisson's ratio, and many other parameters were calcd. using the PBEsol and vdW approxns. Also, in this work, utilizing a new accuracy in calcg. the elastic consts., the intense conflict between the previous theor. results and the exptl. data were fixed. Moreover, for the first time, through combination of the PBEsol and vdW methods, the effect of the interaction between methylammonium and PbX3 scaffold on the mech. properties of lead halide perovskites was well cleared. In continuation, using the PBEsol+vdW method, a phase transition appeared for the MAPbBr3 and MAPbCl3 structures, which proved more stability of MAPbBr3 and MAPbCl3 in comparison with MAPbI3. In what follows, by studying these materials under an applied strain beyond the harmonic region, the transition zone to the plastic area in the strain region of 5.5% and smaller was identified, and the small values of the aforementioned applied strains were found to be the reason for the instability of these materials at room temp. and above.
- 30Yang, D.; Lv, J.; Zhao, X.; Xu, Q.; Fu, Y.; Zhan, F.; Zunger, A.; Zhang, L. Functionality-Directed Screening of Pb-Free Hybrid Organic-Inorganic Perovskites with Desired Intrinsic Photovoltaic Functionalities. Chem. Mater. 2017, 29, 524– 538, DOI: 10.1021/acs.chemmater.6b0322130https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitFOiurzI&md5=a081b09283f5c1cb70acc487384d6c98Functionality-Directed Screening of Pb-Free Hybrid Organic-Inorganic Perovskites with Desired Intrinsic Photovoltaic FunctionalitiesYang, Dongwen; Lv, Jian; Zhao, Xingang; Xu, Qiaoling; Fu, Yuhao; Zhan, Yiqiang; Zunger, Alex; Zhang, LijunChemistry of Materials (2017), 29 (2), 524-538CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The material class of hybrid org.-inorg. perovskites has risen rapidly from a virtually unknown material in photovoltaic applications a short 7 years ago into an ∼20% efficient thin-film solar cell material. As promising as this class of materials is, however, there are limitations assocd. with its poor long-term stability, nonoptimal band gap, presence of environmentally toxic Pb element, etc. We herein apply a functionality-directed theor. materials selection approach as a filter for initial screening of the compds. that satisfy the desired intrinsic photovoltaic functionalities and might overcome the above limitations. First-principles calcns. are employed to systemically study thermodn. stability and photovoltaic-related properties of hundreds of candidate hybrid perovskites. We have identified in this materials selection process 14 Ge- and Sn-based materials with potential superior bulk-material-intrinsic photovoltaic performance. A distinct class of compds. contg. NH3COH+ with the org. mol. derived states intriguingly emerging at band-edges is found. Comparison of various candidate materials offers insights on how compn. variation and microscopic structural changes affect key photovoltaic relevant properties in this family of materials.
- 31Buin, A.; Comin, R.; Xu, J.; Ip, A. H.; Sargent, E. H. Halide-Dependent Electronic Structure of Organolead Perovskite Materials. Chem. Mater. 2015, 27, 4405– 4412, DOI: 10.1021/acs.chemmater.5b0190931https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXpsFOitbo%253D&md5=0cca5a4d89cdea2cebf27e91a8a51cc8Halide-Dependent Electronic Structure of Organolead Perovskite MaterialsBuin, Andrei; Comin, Riccardo; Xu, Jixian; Ip, Alexander H.; Sargent, Edward H.Chemistry of Materials (2015), 27 (12), 4405-4412CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)Organometal halide perovskites have recently attracted tremendous attention both at the exptl. and theor. levels. These materials, in particular methylammonium triiodide, are still limited by poor chem. and structural stability under ambient conditions. Today this represents one of the major challenges for polycryst. perovskite-based photovoltaic technol. In addn. to this, the performance of perovskite-based devices is degraded by deep localized states, or traps. To achieve better-performing devices, it is necessary to understand the nature of these states and the mechanisms that lead to their formation. The major sources of deep traps in the different halide systems have different origin and character. Halide vacancies are shallow donors in I-based perovskites, whereas they evolve into a major source of traps in Cl-based perovskites. Lead interstitials, which can form lead dimers, are the dominant source of defects in Br-based perovskites, in line with recent exptl. data. As a result, the optimal growth conditions are also different for the distinct halide perovskites: growth should be halide-rich for Br and Cl, and halide-poor for I-based perovskites. Stability in relation to the reaction enthalpies of mixts. of bulk precursors with respect to final perovskite product are discussed. Methylammonium lead triiodide was characterized by the lowest reaction enthalpy, explaining its low stability. At the opposite end, the highest stability was found for the methylammonium lead trichloride, also consistent with the authors' exptl. findings which show no observable structural variations over an extended period of time.
- 32Zhang, Y.-Y.; Chen, S.; Xu, P.; Xiang, H.; Gong, X.-G.; Walsh, A.; Wei, S.-H. Intrinsic Instability of the Hybrid Halide Perovskite Semiconductor CH3NH3PbI3. arXiv.org, e-Print Arch., Condens. Matter 2015, arXiv:1506.01301 DOI: 10.1088/0256-307X/35/3/036104There is no corresponding record for this reference.
- 33Buin, A.; Pietsch, P.; Xu, J.; Voznyy, O.; Ip, A. H.; Comin, R.; Sargent, E. H. Materials Processing Routes to Trap-Free Halide Perovskites. Nano Lett. 2014, 14, 6281– 6286, DOI: 10.1021/nl502612m33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslagurzF&md5=c0f902453e55d5a93ec2bf3cded2224eMaterials Processing Routes to Trap-Free Halide PerovskitesBuin, Andrei; Pietsch, Patrick; Xu, Jixian; Voznyy, Oleksandr; Ip, Alexander H.; Comin, Riccardo; Sargent, Edward H.Nano Letters (2014), 14 (11), 6281-6286CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Photovoltaic devices based on lead iodide perovskite films have seen rapid advancements, recently achieving an impressive 17.9% certified solar power conversion efficiency. Reports have consistently emphasized that the specific choice of growth conditions and chem. precursors is central to achieving superior performance from these materials; yet the roles and mechanisms underlying the selection of materials processing route is poorly understood. Films grown under iodine-rich conditions are prone to a high d. of deep electronic traps (recombination centers), while the use of a chloride precursor avoids the formation of key defects (Pb atom substituted by I) responsible for short diffusion lengths and poor photovoltaic performance. Also, the lowest-energy surfaces of perovskite crystals are entirely trap-free, preserving both electron and hole delocalization to a remarkable degree, helping to account for explaining the success of polycryst. perovskite films. The authors construct perovskite films from I-poor conditions using a lead acetate precursor, and the authors' measurement of a long (600 ± 40 nm) diffusion length confirms this new picture of the importance of growth conditions.
- 34Tenuta, E.; Zheng, C.; Rubel, O. Thermodynamic Origin of Instability in Hybrid Halide Perovskites. Sci. Rep. 2016, 6, 37654, DOI: 10.1038/srep3765434https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitFSmtbvJ&md5=cdf310db5f6822b0dea11f0b16d9a978Thermodynamic origin of instability in hybrid halide perovskitesTenuta, E.; Zheng, C.; Rubel, O.Scientific Reports (2016), 6 (), 37654CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)Degrdn. of hybrid halide perovskites under the influence of environmental factors impairs future prospects of using these materials as absorbers in solar cells. First principle calcns. can be used as a guideline in search of new materials, provided we can rely on their predictive capabilities. We show that the instability of perovskites can be captured using ab initio total energy calcns. for reactants and products augmented with addnl. thermodn. data to account for finite temp. effects. Calcns. suggest that the instability of CH3NH3PbI3 in moist environment is linked to the aq. soly. of the CH3NH3I salt, thus making other perovskite materials with sol. decompn. products prone to degrdn. Properties of NH3OHPbI3, NH3NH2PbI3, PH4PbI3, SbH4PbI3, CsPbBr3, and a new hypothetical SF3PbI3 perovskite are studied in the search for alternative solar cell absorber materials with enhanced chem. stability.
- 35Ganose, A. M.; Savory, C. N.; Scanlon, D. O. (CH3NH3)2Pb(SCN)2I2: A More Stable Structural Motif for Hybrid Halide Photovoltaics ?. J. Phys. Chem. Lett. 2015, 6, 4594– 4598, DOI: 10.1021/acs.jpclett.5b0217735https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhslGms7bK&md5=7cb162d005a67d7418b9ef5ee761df6f(CH3NH3)2Pb(SCN)2I2: A New More Stable Structural Motif for Hybrid Halide Photovoltaics?Ganose, Alex M.; Savory, Christopher N.; Scanlon, David O.Journal of Physical Chemistry Letters (2015), 6 (22), 4594-4598CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Hybrid halide perovskites have recently emerged as a highly efficient class of light absorbers; however, there are increasing concerns over their long-term stability. Recently, incorporation of SCN- was suggested as a novel route to improving stability without neg. impacting performance. Intriguingly, despite crystg. in a 2-dimensional layered structure, (CH3NH3)2Pb(SCN)2I2 (MAPSI) possesses an ideal band gap of 1.53 eV, close to that of the 3-dimensional connected champion hybrid perovskite absorber, CH3NH3PbI3 (MAPI). Here, the authors identify, using hybrid d. functional theory, the origin of the smaller than expected band gap of MAPSI through a detailed comparison with the electronic structure of MAPI. Also, assessment of the MAPSI structure reveals that it is thermodynamically stable with respect to phase sepn., a likely source of the increased stability reported in expt.
- 36Zheng, C.; Rubel, O. Ionization Energy as a Stability Criterion for Halide Perovskites. J. Phys. Chem. C 2017, 121, 11977– 11984, DOI: 10.1021/acs.jpcc.7b0033336https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXns1Ontrs%253D&md5=e050eee4490f3cecf84aa925113e1c95Ionization Energy as a Stability Criterion for Halide PerovskitesZheng, Chao; Rubel, OlegJournal of Physical Chemistry C (2017), 121 (22), 11977-11984CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Instability of hybrid org.-inorg. halide perovskites hinders their development for photovoltaic applications. First-principles calcns. were used for evaluation of a decompn. reaction enthalpy of hybrid halide perovskites, which is linked to exptl. obsd. degrdn. of device characteristics. However, simple criteria for predicting the intrinsic stability of halide perovskites are lacking since Goldschmidt's tolerance and octahedral geometrical factors do not fully capture formability of those perovskites. The authors extend the Born-Haber cycle to partition the reaction enthalpy of various perovskite structures into lattice, ionization, and molecularization energy components. The anal. of various contributions to the reaction enthalpy points to an ionization energy of an org. mol. and an inorg. complex ion as an addnl. criterion for predicting chem. trends in stability of hybrid halide perovskites. The ionization energy equal to or less than that for cesium and the size comparable to that of methylammonium define the design space for cations A+ in the search for new perovskite structures APbI3 with improved chem. stability that are suitable for photovoltaic applications.
- 37Yang, B.; Dyck, O.; Ming, W.; Du, M.-H.; Das, S.; Rouleau, C. M.; Duscher, G.; Geohegan, D. B.; Xiao, K. Observation of Nanoscale Morphological and Structural Degradation in Perovskite Solar Cells by in Situ TEM. ACS Appl. Mater. Interfaces 2016, 8, 32333– 32340, DOI: 10.1021/acsami.6b1134137https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvVSjur7M&md5=3c22e4bc4468498904d7a761cbdd0293Observation of Nanoscale Morphological and Structural Degradation in Perovskite Solar Cells by in Situ TEMYang, Bin; Dyck, Ondrej; Ming, Wenmei; Du, Mao-Hua; Das, Sanjib; Rouleau, Christopher M.; Duscher, Gerd; Geohegan, David B.; Xiao, KaiACS Applied Materials & Interfaces (2016), 8 (47), 32333-32340CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)High-resoln. in situ transmission electron microscopy (TEM) and electron energy loss spectroscopy were applied to systematically investigate morphol. and structural degrdn. behaviors in perovskite films during different environmental exposure treatments. In situ TEM expt. indicates that vacuum itself is not likely to cause degrdn. in perovskites. In addn., these materials were found to degrade significantly when they were heated to ∼50-60 °C (i.e., a solar cell's field operating temp.) under illumination. This observation thus conveys a critically important message that the instability of perovskite solar cells at such a low temp. may limit their real field com. applications. It was further unveiled that oxygen most likely attacks the CH3NH3+ org. moiety rather than the PbI6 component of perovskites during ambient air exposure at room temp. This finding grants a deeper understanding of the perovskite degrdn. mechanism and suggests a way to prevent degrdn. of perovskites by tailoring the org. moiety component.
- 38Agiorgousis, M. L.; Sun, Y.-Y.; Zeng, A.; Zhang, S. Strong Covalency-Induced Recombination Centers in Perovskite Solar Cell Material CH3NH3PbI3. J. Am. Chem. Soc. 2014, 136, 14570– 14575, DOI: 10.1021/ja507930538https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsFyjtbnE&md5=6231d3e9862a08628d8eebe695356b68Strong Covalency-Induced Recombination Centers in Perovskite Solar Cell Material CH3NH3PbI3Agiorgousis, Michael L.; Sun, Yi-Yang; Zeng, Hao; Zhang, ShengbaiJournal of the American Chemical Society (2014), 136 (41), 14570-14575CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Inorg.-org. hybrid perovskites are a new family of solar cell materials, which have recently been used to make solar cells with efficiency approaching 20%. Here, we report the unique defect chem. of the prototype material, CH3NH3PbI3, based on first-principles calcn. We found that both the Pb cations and I anions in this material exhibit strong covalency as characterized by the formation of Pb dimers and I trimers with strong covalent bonds at some of the intrinsic defects. The Pb dimers and I trimers are only stabilized in a particular charge state with significantly lowered energy, which leads to deep charge-state transition levels within the band gap, in contradiction to a recent proposal that this system has only shallow intrinsic defects. Our results show that, in order to prevent the deep-level defects from being effective recombination centers, the equil. carrier concns. should be controlled so that the Fermi energy is about 0.3 eV away from the band edges. Beyond this range, according to a Shockley-Read-Hall anal., the nonequil. carrier lifetime will be strongly affected by the concn. of I vacancies and the anti-site defects with I occupying a CH3NH3 site.
- 39Haruyama, J.; Sodeyama, K.; Han, L.; Tateyama, Y. Termination Dependence of Tetragonal CH3NH3PbI3 Surfaces for Perovskite Solar Cells. J. Phys. Chem. Lett. 2014, 5, 2903– 2909, DOI: 10.1021/jz501510v39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtleqtLfO&md5=45b2397926d439305279faad86275965Termination Dependence of Tetragonal CH3NH3PbI3 Surfaces for Perovskite Solar CellsHaruyama, Jun; Sodeyama, Keitaro; Han, Liyuan; Tateyama, YoshitakaJournal of Physical Chemistry Letters (2014), 5 (16), 2903-2909CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)We investigated the termination dependence of structural stability and electronic states of the representative (110), (001), (100), and (101) surfaces of tetragonal CH3NH3PbI3 (MAPbI3), the main component of a perovskite solar cell (PSC), by d. functional theory calcns. By examg. various types of PbIx polyhedron terminations, we found that a vacant termination is more stable than flat termination on all of the surfaces, under thermodn. equil. conditions of bulk MAPbI3. More interestingly, both terminations can coexist esp. on the more probable (110) and (001) surfaces. The electronic structures of the stable vacant and PbI2-rich flat terminations on these two surfaces largely maintain the characteristics of bulk MAPbI3 without midgap states. Thus, these surfaces can contribute to the long carrier lifetime actually obsd. for the PSCs. Furthermore, the shallow surface states on the (110) and (001) flat terminations can be efficient intermediates of hole transfer. Consequently, the formation of the flat terminations under the PbI2-rich condition will be beneficial for the improvement of PSC performance.
- 40Yin, W.- J.; Shi, T.; Yan, Y. Unusual Defect Physics in CH3NH3PbI3 Perovskite Solar Cell Absorbers. Appl. Phys. Lett. 2014, 104, 063903, DOI: 10.1063/1.4864778There is no corresponding record for this reference.
- 41Onoda-Yamamuro, N.; Matsuo, T.; Suga, H. Calorimetric and IR Spectroscopic Studies of Phase Transitions in Methylammonium Trihalogenoplumbates (II). J. Phys. Chem. Solids 1990, 51, 1383– 1395, DOI: 10.1016/0022-3697(90)90021-741https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXhtFahsL4%253D&md5=e87ac8ccd0e391890852451c44f992d9Calorimetric and IR spectroscopic studies of phase transitions in methylammonium trihaloplumbates(II)Onoda-Yamamuro, Noriko; Matsuo, Takasuke; Suga, HiroshiJournal of Physics and Chemistry of Solids (1990), 51 (12), 1383-95CODEN: JPCSAW; ISSN:0022-3697.Heat capacities of CH3NH3PbX3(X = Cl, Br, I) were measured at 13-300 K (365 K for the I). Two anomalies were found in the Cl and the I, and 3 in the Br. All the phase transitions were of the 1st order, although the highest temp. transitions in the Br and the I were close to 2nd order. Their temps. and entropies are given.
- 42Glasser, L.; Jenkins, D. D. B. Standard Absolute Entropies, S°298, from Volume or Density. Part II. Organic Liquids and Solids. Thermochim. Acta 2004, 414, 125– 130, DOI: 10.1016/j.tca.2003.12.00642https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXjsVCrsb4%253D&md5=d7870a85fb38d213e185774ea460490dStandard absolute entropies, S298°, from volume or density. Part II. Organic liquids and solidsGlasser, Leslie; Jenkins, H. Donald BrookeThermochimica Acta (2004), 414 (2), 125-130CODEN: THACAS; ISSN:0040-6031. (Elsevier Science B.V.)The std. abs. entropies of many materials are unknown, which precludes a full understanding of their thermodn. stabilities. We show, for both org. liqs. and solids, that entropies are reliably linearly correlated with vol. per mol., Vm (nm3 per mol.) (or molar volume, M/ρ (cm3 mol-1)); thus, permitting simple evaluation of std. entropies (J K-1 mol-1) at 298 K. The regression lines generally pass close to the origin, with the following formulas: for org. liqs., S298°(l) (J K-1 mol-1) = 1133Vm + 44 or S298°(l) (J K-1 mol-1) = 1.881M/ρ + 44; for org. solids, S298°(s) (J K-1 mol-1) = 774Vm + 57 or S298°(s) (J K-1 mol-1) = 1.285M/ρ + 57. These results complement similar studies (by ourselves and others) demonstrating linear entropy-vol. correlations for ionic solids (including minerals, simple ionic solids, and ionic hydrates and solvates).
- 43El-Mellouhi, F.; Bentria, E. T.; Rashkeev, S. N.; Kais, S.; Alharbi, F. H. Enhancing Intrinsic Stability of Hybrid Perovskite Sola Cell by Strong, yet Balanced, Electronic Coupling. Sci. Rep. 2016, 6, 30305, DOI: 10.1038/srep3030543https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht12gu7vI&md5=c35c71967d3bc68788806f8e738b47d2Enhancing Intrinsic Stability of Hybrid Perovskite Solar Cell by Strong, yet Balanced, Electronic CouplingEl-Mellouhi, Fedwa; Bentria, El Tayeb; Rashkeev, Sergey N.; Kais, Sabre; Alharbi, Fahhad H.Scientific Reports (2016), 6 (), 30305CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)In the past few years, the meteoric development of hybrid org.-inorg. perovskite solar cells (PSC) astonished the community. The efficiency has already reached the level needed for commercialization; however, the instability hinders its deployment on the market. Here, we report a mechanism to chem. stabilize PSC absorbers. We propose to replace the widely used methylammonium cation (CH3NH3+) by alternative mol. cations allowing an enhanced electronic coupling between the cation and the PbI6 octahedra while maintaining the band gap energy within the suitable range for solar cells. The mechanism exploits establishing a balance between the electronegativity of the materials' constituents and the resulting ionic electrostatic interactions. The calcns. demonstrate the concept of enhancing the electronic coupling, and hence the stability, by exploring the stabilizing features of CH3PH3+, CH3SH2+, and SH3+ cations, among several other possible candidates. Chem. stability enhancement hence results from a strong, yet balanced, electronic coupling between the cation and the halides in the octahedron. This shall unlock the hindering instability problem for PSCs and allow them to hit the market as a serious low-cost competitor to silicon based solar cell technologies.
- 44Chun-Ren Ke, J.; Walton, A. S.; Lewis, D. J.; Tedstone, A.; O’Brien, P.; Thomas, A. G.; Flavell, W. R. In situ Investigation of Degradation at Organometal Halide Perovskite Surfaces by X-Ray Photoeectron Spectroscopy at Realistic Water Vapour Pressure. Chem. Commun. 2017, 53, 5231, DOI: 10.1039/C7CC01538KThere is no corresponding record for this reference.
- 45Hong, F.; Saparov, B.; Meng, W.; Xiao, Z.; Mitzi, D. B.; Yan, Y. Viability of Lead-Free Perovskites with Mixed Chalcogen and Halogen Anions for Photovoltaic Applications. J. Phys. Chem. C 2016, 120, 6435– 6441, DOI: 10.1021/acs.jpcc.6b0092045https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjvVGjsrw%253D&md5=fa35a1bdcc705c34cbcc9d79fbe3166fViability of Lead-Free Perovskites with Mixed Chalcogen and Halogen Anions for Photovoltaic ApplicationsHong, Feng; Saparov, Bayrammurad; Meng, Weiwei; Xiao, Zewen; Mitzi, David B.; Yan, YanfaJournal of Physical Chemistry C (2016), 120 (12), 6435-6441CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The authors assess the viability for photovoltaic applications of proposed Pb-free perovskites with mixed chalcogen and halogen anions, AB(Ch,X)3 (A = Cs or Ba; B = Sb or Bi; Ch = chalcogen; X = halogen), by examg. crit. issues such as the structural, electronic/optical properties, and stability through the combination of d.-functional theory calcns. and solid-state reactions. The calcns. show that these quaternary Pb-free perovskites are thermodynamically unstable-they are prone to decomp. into ternary and/or binary secondary phases or form phases with nonperovskite structures. Solid-state synthesis efforts confirm the theor. predicted difficulty for prepg. these compds.; all attempted reactions do not form the desired perovskite phases with mixed chalcogen and halogen anions under conditions examd. Instead, they form sep. binary and ternary compds. Despite earlier predictions of promising characteristics for these prospective perovskites for photovoltaics, the results suggest that, due to their instability, the Pb-free perovskites with mixed chalcogen and halogen anions may be challenging to form under equil. synthetic conditions.
- 46Kim, N.-K.; Min, Y. H.; Noh, S.; Cho, E.; Jeong, G.; Joo, M.; Ahn, S.-W.; Lee, J. S.; Kim, S.; Ihm, K.; Ahn, H. Investigation of Thermally Induced Degradation in CH3NH3PbI3 Perovskite Solar Cells Using In-situ Synchrotron Radiation Analysis. Sci. Rep. 2017, 7, 4645, DOI: 10.1038/s41598-017-04690-w46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1cjkvVWksA%253D%253D&md5=3799e89322ddb5bfd60f8da2263cc716Investigation of Thermally Induced Degradation in CH3NH3PbI3 Perovskite Solar Cells using In-situ Synchrotron Radiation AnalysisKim Nam-Koo; Min Young Hwan; Noh Seokhwan; Cho Eunkyung; Jeong Gitaeg; Joo Minho; Ahn Seh-Won; Lee Jeong Soo; Kim Seongtak; Kang Yoonmook; Lee Hae-Seok; Kim Donghwan; Ihm Kyuwook; Ahn HyungjuScientific reports (2017), 7 (1), 4645 ISSN:.In this study, we employ a combination of various in-situ surface analysis techniques to investigate the thermally induced degradation processes in MAPbI3 perovskite solar cells (PeSCs) as a function of temperature under air-free conditions (no moisture and oxygen). Through a comprehensive approach that combines in-situ grazing-incidence wide-angle X-ray diffraction (GIWAXD) and high-resolution X-ray photoelectron spectroscopy (HR-XPS) measurements, we confirm that the surface structure of MAPbI3 perovskite film changes to an intermediate phase and decomposes to CH3I, NH3, and PbI2 after both a short (20 min) exposure to heat stress at 100 °C and a long exposure (>1 hour) at 80 °C. Moreover, we observe clearly the changes in the orientation of CH3NH3(+) organic cations with respect to the substrate in the intermediate phase, which might be linked directly to the thermal degradation processes in MAPbI3 perovskites. These results provide important progress towards improved understanding of the thermal degradation mechanisms in perovskite materials and will facilitate improvements in the design and fabrication of perovskite solar cells with better thermal stability.
- 47Song, Z.; Watthage, S. C.; Phillips, A. B.; Tompkins, B. L.; Ellingson, R. J.; Heben, M. J. Impact of Processing Temperature and Composition on the Formation of Methylammonium Lead Iodide Perovskites. Chem. Mater. 2015, 27, 4612– 4619, DOI: 10.1021/acs.chemmater.5b0101747https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXosVCgsrs%253D&md5=ecce420966bae0b8ca34931601860181Impact of Processing Temperature and Composition on the Formation of Methylammonium Lead Iodide PerovskitesSong, Zhaoning; Watthage, Suneth C.; Phillips, Adam B.; Tompkins, Brandon L.; Ellingson, Randy J.; Heben, Michael J.Chemistry of Materials (2015), 27 (13), 4612-4619CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)A delicate control of the stoichiometry, crystallog. phase, and grain structure of the photoactive material is typically required to fabricate high-performance photovoltaic (PV) devices. Organo-metal halide perovskite materials, however, exhibit a large degree of tolerance in synthesis and can be fabricated into high efficiency devices by a variety of different vacuum and soln.-based processes, with a wide range of precursor ratios. Probably the phase field for the desired material is wider than expected or that high device efficiency may be achieved with a range of phases. Here, the authors study the structural and optical properties of the materials formed when a range of compns. of methylammonium iodide (MAI) and lead iodide (PbI2) were reacted at 40-190°. The reactions were performed according to a commonly employed synthetic approach for high efficiency PV devices, and the data was analyzed to construct a pseudobinary, temp.-dependent, phase-compn. processing diagram. Escape of MAI vapor at the highest temps. (150-190°) enabled a PbI2 phase to persist to very high MAI concns., and the processing diagram was not representative of phase equil. in this range. Data from reactions performed with a fixed vapor pressure of MAI allowed the high temp. portion of the diagram to be cor. and a near-equil. phase diagram to be proposed. The perovskite phase field is wider than previously thought under both processing conditions and extended by the existence of stacked perovskite sheet phases. Several aspects of the diagrams clarify why the organo-halide perovskite materials are compatible with soln. processing.
- 48Leyden, M. R.; Meng, L.; Jiang, Y.; Ono, L. K.; Qiu, L.; Juarez-Perez, E. J.; Qin, C.; Adachi, C.; Qi, Y. Methylammonium Lead Bromide Perovskite Light-Emitting Diodes by Chemical Vapor deposition. J. Phys. Chem. Lett. 2017, 8, 3193– 3198, DOI: 10.1021/acs.jpclett.7b0109348https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVKisbrL&md5=96c91cb7f5f53c11ec06d701646a11cdMethylammonium Lead Bromide Perovskite Light-Emitting Diodes by Chemical Vapor DepositionLeyden, Matthew R.; Meng, Lingqiang; Jiang, Yan; Ono, Luis K.; Qiu, Longbin; Juarez-Perez, Emilio J.; Qin, Chuanjiang; Adachi, Chihaya; Qi, YabingJournal of Physical Chemistry Letters (2017), 8 (14), 3193-3198CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Organo-Pb-halide perovskites are promising materials for optoelectronic applications. Perovskite solar cells have reached power conversion efficiencies of >22%, and perovskite light-emitting diodes (LEDs) have recently achieved >11% external quantum efficiency. To date, most research on perovskite LEDs has focused on soln.-processed films. There are many advantages of a vapor-based growth process to prep. perovskites, including ease of patterning, ability to batch process, and material compatibility. An all-vapor perovskite growth process by CVD was studied, and luminance ≤560 cd/m2 was demonstrated.
- 49Juarez-Perez, E. J.; Hawash, Z.; Raga, S. R.; Ono, L. K.; Qi, Y. Thermal Degradation of CH3NH3PbI3 Perovskite into NH3 and CH3I Gases Observed by Coupled Thermogravimetry-Mass Spectrometry Analysis. Energy Environ. Sci. 2016, 9, 3406– 3410, DOI: 10.1039/C6EE02016J49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVKjtLjM&md5=c6c03d9dbf93e71a54a56d5cf9d7f000Thermal degradation of CH3NH3PbI3 perovskite into NH3 and CH3I gases observed by coupled thermogravimetry-mass spectrometry analysisJuarez-Perez, Emilio J.; Hawash, Zafer; Raga, Sonia R.; Ono, Luis K.; Qi, YabingEnergy & Environmental Science (2016), 9 (11), 3406-3410CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)Thermal gravimetric and DTA (TG-DTA) coupled with quadrupole mass spectrometry (MS) and first principles calcns. were employed to elucidate the chem. nature of released gases during the thermal decompn. of CH3NH3PbI3. In contrast to the common wisdom that CH3NH3PbI3 is decompd. into CH3NH2 and HI, the major gases were methyliodide (CH3I) and ammonia (NH3). We anticipate that our findings will provide new insights into further formulations of the perovskite active material and device design that can prevent methylammonium decompn. and thus increase the long-term stability of perovskite-based optoelectronic devices.
- 50Latini, A.; Gigli, G.; Ciccioli, A. A Study on the Nature of the Thermal Decomposition of Methylammonium Lead Iodide Perovskite CH3NH3PbI3: An attempt to Rationalise Contradictory Experimental Results. Sustainable Energy Fuels 2017, 1, 1351, DOI: 10.1039/C7SE00114B50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1CrsLrL&md5=c942e4c428cd439c6f0d65b304522ea2A study on the nature of the thermal decomposition of methylammonium lead iodide perovskite, CH3NH3PbI3: an attempt to rationalise contradictory experimental resultsLatini, Alessandro; Gigli, Guido; Ciccioli, AndreaSustainable Energy & Fuels (2017), 1 (6), 1351-1357CODEN: SEFUA7; ISSN:2398-4902. (Royal Society of Chemistry)The nature of the gas phase product released during the thermal decompn. of CH3NH3PbI3 (methylammonium lead iodide) to PbI2 (lead diiodide) under vacuum is discussed on the basis of thermodn. predictions, recently published exptl. results, and new expts. presented here. From the limited data currently available, the nature of the main decompn. path is not clear because, both, the process releasing HI(g) + CH3NH2(g) and that leading to NH3(g) + CH3I(g) were obsd. under different conditions. Our thermodn. anal. showed that process is largely favored for all the CH3NH3PbX3 (X = Cl, Br, I) compds. However, Knudsen effusion mass spectrometry expts. (temp. range 140-240 °C) showed that HI(g) and CH3NH2(g) were the predominant species in the vapor, with process occurring to a much smaller extent than suggested by the thermodn. driving force, thus being of minor importance under effusion conditions. We also found that this process was comparatively enhanced by high temps. and low effusion rates (high impedance orifice). Our exptl. evidence suggested that the thermodynamically favored process was affected by a significant kinetic hindrance. Overall, the prevailing decompn. path is likely to markedly depend on the actual operative conditions.
- 51Deretzis, I.; Alberti, A.; Pellegrino, G.; Smecca, E.; Giannazzo, F.; Sakai, N.; Miyasaka, T.; LaMagna, A. Atomistic Origins of CH3NH3PbI3 degradation to PbI2 in vacuum. Appl. Phys. Lett. 2015, 106, 131904, DOI: 10.1063/1.491682151https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlslCntLs%253D&md5=6e80b96477b15ae873f7a2926a0337efAtomistic origins of CH3NH3PbI3 degradation to PbI2 in vacuumDeretzis, I.; Alberti, A.; Pellegrino, G.; Smecca, E.; Giannazzo, F.; Sakai, N.; Miyasaka, T.; La Magna, A.Applied Physics Letters (2015), 106 (13), 131904/1-131904/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)We study the mechanisms of CH3NH3PbI3 degrdn. and its transformation to PbI2 by means of X-ray diffraction and the d. functional theory. The exptl. anal. shows that the material can degrade in both air and vacuum conditions, with humidity and temp.-annealing strongly accelerating such process. Based on ab initio calcns., we argue that even in the absence of humidity, a decompn. of the perovskite structure can take place through the statistical formation of mol. defects with a non-ionic character, whose volatility at surfaces should break the thermodn. defect equil. We finally discuss the strategies that can limit such phenomenon and subsequently prolong the lifetime of the material. (c) 2015 American Institute of Physics.
- 52Stoumpos, C. C.; Malliakas, C. D.; Kanatzidis, M. G. Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties. Inorg. Chem. 2013, 52, 9019– 9038, DOI: 10.1021/ic401215x52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtVGqsL3N&md5=94c35d645dcd9770b4097d0bd440269bSemiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent PropertiesStoumpos, Constantinos C.; Malliakas, Christos D.; Kanatzidis, Mercouri G.Inorganic Chemistry (2013), 52 (15), 9019-9038CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)A broad org.-inorg. series of hybrid metal iodide perovskites AMI3, where A is the methylammonium (MeNH3+) or formamidinium (HC(NH2)2+) cation and M is Sn (1 and 2) or Pb (3 and 4) are reported. The compds. were prepd. through a variety of synthetic approaches, and the nature of the resulting materials is discussed in terms of their thermal stability and optical and electronic properties. The chem. and phys. properties of these materials strongly depend on the prepn. method. Single crystal x-ray diffraction anal. of 1-4 classifies the compds. in the perovskite structural family. Structural phase transitions were obsd. and studied by temp.-dependent single crystal x-ray diffraction in the 100-400 K range. The charge transport properties of the materials are discussed in conjunction with diffuse reflectance studies in the mid-IR region that display characteristic absorption features. Temp.-dependent studies show a strong dependence of the resistivity as a function of the crystal structure. Optical absorption measurements indicate that 1-4 behave as direct-gap semiconductors with energy band gaps distributed at 1.25-1.75 eV. The compds. exhibit an intense near-IR luminescence (PL) emission in the 700-1000 nm range (1.1-1.7 eV) at room temp. Solid solns. between the Sn and Pb compds. are readily accessible throughout the compn. range. The optical properties such as energy band gap, emission intensity, and wavelength can be readily controlled for the isostructural series of solid solns. MeNH3Sn1-xPbxI3 (5). The charge transport type in these materials was characterized by Seebeck coeff. and Hall-effect measurements. The compds. behave as p- or n-type semiconductors depending on the prepn. method. The samples with the lowest carrier concn. are prepd. from soln. and are n-type; p-type samples can be obtained through solid state reactions exposed in air in a controllable manner. In the case of Sn compds., there is a facile tendency toward oxidn. which causes the materials to be doped with Sn4+ and thus behave as p-type semiconductors displaying metal-like cond. The compds. appear to possess very high estd. electron and hole mobilities that exceed 2000 cm2/(V s) and 300 cm2/(V s), resp., as shown in the case of MeNH3SnI3 (1). The authors also compare the properties of the title hybrid materials with those of the all-inorg. CsSnI3 and CsPbI3 prepd. using identical synthetic methods.
- 53Dimesso, L.; Dimamay, M.; Hamburger, M.; Jaegermann, W. Properties of CH3NH3PbX3 (X = I, Br, Cl) Powders as Precursors for Organic/Inorganic Solar Cells. Chem. Mater. 2014, 26, 6762– 6770, DOI: 10.1021/cm503240k53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvFaqu7bF&md5=a2e05a7682d381a74647fa66b7909c45Properties of CH3NH3PbX3 (X = I, Br, Cl) Powders as Precursors for Organic/Inorganic Solar CellsDimesso, L.; Dimamay, M.; Hamburger, M.; Jaegermann, W.Chemistry of Materials (2014), 26 (23), 6762-6770CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The MeNH3PbX3 (X = Cl, Br, I) perovskites were prepd. by a self-organization processes using different precursor solns. The XRD anal. indicates the formation, at room temp., of a tetragonal structure (space group I4/mcm) for X = I, of a cubic structure (space group Pm‾3m) for X = Br, and of centro-sym. cubic structure (space group Pm3m) for X = Cl, resp. The structural anal. revealed the formation of MeNH3Cl as secondary phase in the Cl-contg. system. The morphol. study revealed the formation of rhombo-hexagonal dodecahedra crystallite for X = I, Br, whereas cube-like aggregates were obsd. for X = Cl. The TGA performed in air did not reveal any loss until 250° for X = I and 300° for X = Br, resp., whereas the DTA detected 2 endothermic thermal events (at 336 and 409°) for X = I and one only (379°) for X = Br, resp. The IR spectra (IR) of the powders conformed to the 3-fold symmetry of the methylammonium ion which rotates around the C-N axis. Optical absorption measurements indicated that the MeNH3PbX3 systems behave as direct-gap semiconductors with energy band gaps of 1.53 eV for X = I, 2.20 eV for X = Br, and 3.00 eV for X = Cl, resp., at room temp. The direct-gap semicond. for X = I and X = Br was confirmed by the photoluminescence emission measurements, whereas the compd. for X = Cl is inactive. Iodine-contg. powders were dissolved in an org. solvent (dimethyl-formamide, DMF). The dispersion (100-300 μL) was dropped on glassy substrates on which thick films were obtained by spin-coating and thermal treatment at 120° for ∼5 min. The prepn. of the layers was performed in air at room temp.
- 54Nenon, D. P.; Christians, J. A.; Wheeler, L. M.; Blackburn, J. L.; Sanehira, E. M.; Dou, B.; Olsen, M. L.; Zhu, K.; Berry, J. J.; Luther, J. M. Structural and Chemical Evolution of Methylammonium Lead Halide Perovskites During Thermal Processing from Solution. Energy Environ. Sci. 2016, 9, 2072– 2082, DOI: 10.1039/C6EE01047D54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmvFylurk%253D&md5=c9bcf86e4e67ed408c5a0516ad3ba84eStructural and chemical evolution of methylammonium lead halide perovskites during thermal processing from solutionNenon, David P.; Christians, Jeffrey A.; Wheeler, Lance M.; Blackburn, Jeffrey L.; Sanehira, Erin M.; Dou, Benjia; Olsen, Michele L.; Zhu, Kai; Berry, Joseph J.; Luther, Joseph M.Energy & Environmental Science (2016), 9 (6), 2072-2082CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)Following the prominent success of CH3NH3PbI3 in photovoltaics and other optoelectronic applications, focus has been placed on better understanding perovskite crystn. from precursor and intermediate phases in order to facilitate improved crystallinity often desirable for advancing optoelectronic properties. Understanding of stability and degrdn. is also of crit. importance as these materials seek com. applications. In this study, we investigate the evolution of perovskites formed from targeted precursor chemistries by correlating in situ temp.-dependent X-ray diffraction, thermogravimetric anal., and mass spectral anal. of the evolved species. This suite of analyses reveals important precursor compn.-induced variations in the processes underpinning perovskite formation and degrdn. The addn. of Cl- leads to widely different precursor evolution and perovskite formation kinetics, and results in significant changes to the degrdn. mechanism, including suppression of cryst. PbI2 formation and modification of the thermal stability of the perovskite phase. This work highlights the role of perovskite precursor chem. in both its formation and degrdn.
- 55Kottokkaran, R.; Abbas, H.; Balaji, G.; Zhang, L.; Samiee, M.; Kitahara, A.; Noack, M.; Dalal, V. Highly Reproducible Vapor Deposition Technique, Device Physics and Structural Instability of Perovskite Solar Cells. IEEE 42nd Photovoltaic Specialist Conference (PVSC) 2015, 42, 1– 4, DOI: 10.1109/PVSC.2015.7355612There is no corresponding record for this reference.
- 56Williams, A. E.; Holliman, P. J.; Carnie, M. J.; Davies, M. L.; Worsley, D. A.; Watson, T. M. Perovskite Processing for Photovoltaics: A Spectrothermal Evaluation. J. Mater. Chem. A 2014, 2, 19338– 19346, DOI: 10.1039/C4TA04725G56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslaisrjJ&md5=5e7ba07965dcce4306da59652e02eeedPerovskite processing for photovoltaics: a spectro-thermal evaluationWilliams, Alice E.; Holliman, Peter J.; Carnie, Matthew J.; Davies, Matthew L.; Worsley, David A.; Watson, Trystan M.Journal of Materials Chemistry A: Materials for Energy and Sustainability (2014), 2 (45), 19338-19346CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)Thermal anal. (TGA and DSC), coupled with evolved gas FTIR spectroscopy, has been used to study the changes occurring during, and differences between materials after, the annealing step of mixed-halide methylammonium lead halide perovskites. This is important because, to date, the material is the most efficient light harvester in highly efficient, 3rd generation perovskite photovoltaic devices, and processing plays a significant role in device performance. TGA-FTIR data show only solvent evolution during the annealing step, while post-annealing anal. shows that the resulting material still contains a significant amt. of residual solvent; however, efficient DMF removal was possible using a silica gel desiccant for a period of 3 days. The data also show that methylammonium halide decompn. does not occur until temps. are well above those used for perovskite processing, suggesting that this is not a significant issue for device manuf. The absence of a well-defined, reversible tetragonal-cubic phase change around 55° in the DSC data of the annealed material, and the presence of HCl in evolved gas analyzed following thermal decompn., demonstrates that CH3NH3I3-xClx does retain some Cl after annealing and does not simply form stoichiometric CH3NH3PbI3 as has been suggested by some workers.
- 57Showman, A. P. Hydrogen Halides on Jupiter and Saturn. Icarus 2001, 152, 140– 150, DOI: 10.1006/icar.2001.6614There is no corresponding record for this reference.
- 58Jay, A. N.; Daniel, K. A.; Patterson, E. V. Atom-Centered Density Matrix Propagation Calculations on the Methyl Transfer from CH3Cl to NH3: Gas-Phase and Continuum-Solvated Trajectories. J. Chem. Theory Comput. 2007, 3, 336– 343, DOI: 10.1021/ct600280358https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXnvVegtQ%253D%253D&md5=5b0000151f50ce6a49fb727c2e2951bcAtom-Centered Density Matrix Propagation Calculations on the Methyl Transfer from CH3Cl to NH3: Gas-Phase and Continuum-Solvated TrajectoriesJay, Ashley N.; Daniel, Kelly A.; Patterson, Eric V.Journal of Chemical Theory and Computation (2007), 3 (2), 336-343CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)Atom-centered d. matrix propagation (ADMP) calcns. have been carried out to det. gas-phase and continuum-solvated (aq.) trajectories for the Menshutkin reaction of Me chloride with ammonia. The gas-phase trajectories reveal an exit channel that has not been previously reported. The aq. trajectories give the expected results, indicating that solvated ADMP trajectories may be successfully computed using implicit solvation models. The solvated trajectories demonstrate the same stability and convergence qualities as the gas-phase trajectories.
- 59Patterson, E. V. Private communication.There is no corresponding record for this reference.
- 60
Note that, while the derivation of total pressure from KEML measurements requires the gas phase composition to be known, assuming the occurrence of processes 8, 9, or 10 has a very small effect on the calculated pressure, because the relevant average molecular mass of the vapor phase is very similar in all three cases (see ref (27)).
There is no corresponding record for this reference. - 61Łubkowski, J.; Błażejowski, J. Thermal Properties and Thermochemistry of Alkanaminium Bromides. Thermochim. Acta 1990, 157, 259– 277, DOI: 10.1016/0040-6031(90)80027-V61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXktlektrs%253D&md5=d0b732d1794097e06c9a5469a8a43f93Thermal properties and thermochemistry of alkanaminium bromidesLubkowski, Jacek; Blazejowski, JerzyThermochimica Acta (1990), 157 (2), 259-77CODEN: THACAS; ISSN:0040-6031.The thermal behavior of [(CnH2n+1)pNH4-p]Br (n = 0-4 and p = 1-4) was studied by thermoanal. methods (DTA, TG and DTG). All the compds. examd. undergo decompn. upon heating, leading to their total volatilization. In the case of primary, secondary and tertiary amine hydrobromides, the thermal-dissocn. process is accompanied by the release of the appropriate amines and HBr to the gaseous phase. Thermogravimetric curves for these derivs. indicate that the process comprises 2 stages. In both steps thermal dissocn. proceeds via the same chem. mechanism; however, each step is detd. by different kinetics. Quaternary salts decomp. in only 1 step which is accompanied by the release of the appropriate tertiary amines and bromoalkanes to the gaseous phase. The latter process requires that the remarkable activation barrier to be overcome in addn. to that resulting from the thermodn. requirements. On the other hand, the dissociative volatilization of the former derivs. proceeds essentially without any addnl. barrier over that imposed by the enthalpy change for the reaction. The enthalpies of the thermal dissocn. of hydrobromides were evaluated from the nonisothermal thermogravimetric curves, and these values, together with the thermochem. data available in the literature, were used to evaluate the enthalpies of formation and the crystal-lattice energies of the compds. The crystal-lattice energy was also examd. within the Kapustinskii-Yatsimirskii approach, which assumes an additive character of this quantity. The essential thermal and thermochem. characteristics, as well as the influence of the structure of amines on the thermal behavior of alkanaminium bromides are also reviewed and discussed.
- 62Dokurno, P.; Łubkowski, J.; Błażejowski, J. Thermal Properties, Thermolysis and Thermochemistry of Alkanaminium Iodides. Thermochim. Acta 1990, 165, 31– 48, DOI: 10.1016/0040-6031(90)80204-C62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXktFylug%253D%253D&md5=64fce80623f09f1da208cd3b667379ceThermal properties, thermolysis and thermochemistry of alkanaminium iodidesDokurno, Pawel; Lubkowski, Jacek; Blazejowski, JerzyThermochimica Acta (1990), 165 (1), 31-48CODEN: THACAS; ISSN:0040-6031.The thermal features of unbranched compds. of general formula [(CnH2n+1)pNH4-p]I, with n = 0-4 and p = 1-4, were studied by thermoanal. methods (DTA, TG, DTG, and Q-TG). All the compds. studied undergo decompn. upon heating, leading to their total volatilization. In the primary step of the thermal dissocn. of these derivs., HI or RI, in the case of quaternary salts, and the appropriate amines are released in the gaseous phase. This simple thermal decompn. pattern is usually complicated by secondary reactions of an oxidative nature. The latter processes most probably originate from the thermal instability of HI, which can spontaneously decomp. to H2 and I2 giving iodine mols. of high oxidative potential. The enthalpies of the thermal dissocn. were estd. on the basis of the van't Hoff equation using dynamic thermogravimetric curves. Values derived in this way were used together with available literature data to evaluate the enthalpies of formation and the crystal lattice energies of the hydriodides studied. The crystal lattice energy problems were also examd. within the Kapustinskii-Yatsimirskii approach. An attempt was made to describe the kinetics of the thermal decompn. by adopting an Arrhenius model. The influence of the structure of the amines on the thermal behavior of their iodide salts is reviewed and thoroughly discussed.
- 63Sawicka, M.; Storoniak, P.; Skurski, P.; Błażejowski, J.; Rak, J. TG-FTIR, DSC and Quantum Chemical Studies of the Thermal Decomposition of Quaternary Methylammonium Halides. Chem. Phys. 2006, 324, 425– 437, DOI: 10.1016/j.chemphys.2005.11.02363https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XkvFKqt7o%253D&md5=376529aa3bc9877200dc120f42ba4f39TG-FTIR, DSC and quantum chemical studies of the thermal decomposition of quaternary methylammonium halidesSawicka, Marlena; Storoniak, Piotr; Skurski, Piotr; Blazejowski, Jerzy; Rak, JanuszChemical Physics (2006), 324 (2-3), 425-437CODEN: CMPHC2; ISSN:0301-0104. (Elsevier B.V.)The thermal decompn. of quaternary methylammonium halides was studied using thermogravimetry coupled to FTIR (TG-FTIR) and differential scanning calorimetry (DSC) as well as the DFT, MP2, and G2 quantum chem. methods. There is almost perfect agreement between the exptl. IR spectra and those predicted at the B3LYP/6-311G(d,p) level: this has demonstrated for the first time that an equimolar mixt. of trimethylamine and a Me halide is produced as a result of decompn. The exptl. enthalpies of dissocn. are 153.4, 171.2, and 186.7 kJ/mol for chloride, bromide, and iodide, resp.; values that correlate well with the calcd. enthalpies of dissocn. based on crystal lattice energies and quantum chem. thermodn. barriers. The exptl. activation barriers estd. from the least-squares fit of the F1 kinetic model (first-order process) to thermogravimetric traces - 283, 244 and 204 kJ/mol for chloride, bromide, and iodide, resp. - agree very well with theor. calcd. values. The theor. approach assumed in this work has been shown capable of predicting the relevant characteristics of the thermal decompn. of solids with exptl. accuracy.
- 64Dong, C.; Song, X.; Meijer, E. J.; Chen, G.; Xu, Y.; Yu, J. Mechanism Studies on Thermal Dissociation of tri-n-octylamine hydrochloride with FTIR, TG, DSC and quantum chemical methods. J. Chem. Sci. 2017, 129, 1431– 1440, DOI: 10.1007/s12039-017-1357-464https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVCrtrvP&md5=630cf0f8ea8df562a5e3bc307fd092daMechanism studies on thermal dissociation of tri-n-octylamine hydrochloride with FTIR, TG, DSC and quantum chemical methodsDong, Chunhua; Song, Xingfu; Meijer, Evert Jan; Chen, Guilan; Xu, Yanxia; Yu, JianguoJournal of Chemical Sciences (Berlin, Germany) (2017), 129 (9), 1431-1440CODEN: JCSBB5; ISSN:0974-3626. (Springer GmbH)The thermal dissocn. of tri-n-octylamine hydrochloride was investigated using both the quantum chem. simulation and exptl. methods. The pathway through which a mixt. of tri-n-octylamine and hydrogen chloride, rather than di-n-octylamine and 1-chlorooctane, are produced has been detd. through transition state search with intrinsic reaction coordinate calcns. Particularly, strong agreement between the exptl. FTIR spectra and that of TOA demonstrates the same result for the first time. Moreover, the thermal dissocn. of TOAHCl proceeds in two continuous steps, which is different from the low mol. mass amine hydrochlorides. The exptl. enthalpy of the dissocn. was 70.793 kJmol-1 with DSC measurement which is very close to the d. functional theory calcn. result 69.395 kJmol-1. Furthermore, with the aid of DFT calcns., some other important thermochem. characteristics such as crystal lattice energy with the value of 510.597 kJmol-1 were evaluated by means of Born-Fajans-Haber cycle.
- 65https://www.thermocon.org/.There is no corresponding record for this reference.