ACS Publications. Most Trusted. Most Cited. Most Read
Thermodynamic Origin of Photoinstability in the CH3NH3Pb(I1–xBrx)3 Hybrid Halide Perovskite Alloy
More

OR SEARCH CITATIONS

My Activity
Publications

Figure 1Loading Img
Download Hi-Res ImageDownload to MS-PowerPointCite This:J. Phys. Chem. Lett. 2016, 7, 6, 1083-1087
  • Open Access
Letter

Thermodynamic Origin of Photoinstability in the CH3NH3Pb(I1–xBrx)3 Hybrid Halide Perovskite Alloy
Click to copy article linkArticle link copied!

View Author Information
† Centre for Sustainable Chemical Technologies and Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
‡ Universidade Federal da Fronteira Sul, Realeza Paraná 85770-000, Brazil
§ Global E3 Institute and Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea
*E-mail: E-mail: [email protected]
Open PDF

The Journal of Physical Chemistry Letters

Cite this: J. Phys. Chem. Lett. 2016, 7, 6, 1083–1087
Click to copy citationCitation copied!
https://doi.org/10.1021/acs.jpclett.6b00226
Published March 7, 2016

Copyright © 2016 American Chemical Society. This publication is licensed under CC-BY.

Abstract

Click to copy section linkSection link copied!
High Resolution Image
Download MS PowerPoint Slide

The formation of solid-solutions of iodide, bromide, and chloride provides the means to control the structure, band gap, and stability of hybrid halide perovskite semiconductors for photovoltaic applications. We report a computational investigation of the CH3NH3PbI3/CH3NH3PbBr3 alloy from density functional theory with a thermodynamic analysis performed within the generalized quasi-chemical approximation. We construct the phase diagram and identify a large miscibility gap, with a critical temperature of 343 K. The observed photoinstability in some mixed-halide solar cells is explained by the thermodynamics of alloy formation, where an initially homogeneous solution is subject to spinodal decomposition with I and Br-rich phases, which is further complicated by a wide metastable region defined by the binodal line.

Copyright © 2016 American Chemical Society

Subjects

what are subjects

The last four years have seen the emergence of photovoltaic devices based on methylammonium lead iodide (MAPbI3, MA = CH3NH3+) and related hybrid organic–inorganic perovskites. The excitement in the field has led to a large research effort and a rapid development of high-efficiency devices. (1-3) The physical properties of MAPbI3, in particular the band gap, can be tuned in several ways: (i) changing the central organic molecule MA, for example substituting it by the formamidinium (FA); (4) (ii) replacing Pb by another cation, for example Sn or Ge; (5) (iii) substituting iodine by bromine or chlorine.
The first hybrid perovskite photovoltaic devices included small amounts of chlorine, which were believed to be randomly interchanged with iodine forming the MAPb(I1–xClx)3 pseudobinary alloy. Mixed MAPb(I1–xBrx)3 has been recently successfully produced by different groups. (1, 6-11) The motivating factors for the I/Br mixture are increased chemical stability and control of the band gap toward tandem solar cell applications. However, it is still not completely understood whether the alloy is stable against phase segregation in the entire range of composition. There has been some evidence for photoinduced phase separation, (12-14) which can affect measurements and performance when the material is photoexcited. (15, 16) This effect is unusual, as typically electron and ion transport are decoupled (electrons move quickly with short lifetimes compared to slower ion diffusion processes). There have been some initial theoretical studies of the stability of this alloy, but they either focus on a single composition (17) or are based on the inorganic CsPb(I1–xBrx)3 system. (18)
In this Letter we combine first-principles total energy calculations with a statistical mechanical treatment of the configurational space of the solid-solution formed between MAPbI3 and MAPbBr3. From this model, we determine how the thermodynamic potentials of the alloy vary with respect to composition and temperature. From this analysis, we construct the first phase diagram of the system. The qualitative picture that emerges is that the I/Br mixture has a miscibility gap above room temperature and that heavily mixed systems (0.3 < x < 0.6) will be subject to spinodal decomposition and phase separation at 300 K. The main two approximations in our model are the supercell expansion, which limits the configurational space of the alloy that is sampled, and the use of a pseudocubic building block, as the end member compounds and alloys show temperature-dependent structures. (6, 9, 19)
The calculated energy of mixing as a function of the alloy composition is shown in Figure 1. The variation is unusual, as had been already pointed out by Yin et al. for the CsPb(I1–xBrx)3 alloy. (18) The MAPb(I1–xBrx)3 alloy presents a large spread in the energy of mixing in the Br-rich region, which may suggest a tendency for spontaneous ordering in this region at low temperatures. Indeed, there are two configurations that have negative energies of mixing and should be stable against phase separation into the pure end-member compounds, as indicated by the convex hull in Figure 1. These configurations correspond to ordered structures of MAPbIBr2 and MAPbI1/2Br5/2, as shown in Figure 2. Both structures are formed when the iodine ions are located at the apical positions, forming superlattices along the [001] direction. From the Shannon ionic radii, (20) the mismatch between the two halides is 0.24 Å (rI = 2.20 Å, rBr = 1.96 Å). These two ordered structures provide the structural freedom to separate the Pb–I (longer) and Pb–Br (shorter) interatomic separations along distinct directions, so that internal strain is minimized.

Figure 1

Figure 1. Energy of mixing (top) and entropy of mixing (bottom) as functions of the CH3NH3Pb(I1–xBrx)3 alloy composition. The symbols are the values calculated for each configuration (eq 1). The solid lines show the behavior for the alloy at 200 K (blue), 300 K (green) and for a completely random alloy in the high T limit (red) within the generalized quasi-chemical approximation. The dashed line represents the convex hull.

High Resolution Image
Download MS PowerPoint Slide

Figure 2

Figure 2. Stable ordered structures identified for MAPbIBr2 and MAPbI1/2Br5/2, which minimize internal strain arising from the size mismatch between I and Br. The atoms at the corners of the octahedra are the halides Br (orange) and I (pink). The most stable structures are layered with iodine at the apical positions.

High Resolution Image
Download MS PowerPoint Slide
The variation in the energy of mixing of the alloy calculated within the generalized quasi-chemical approximation (GQCA) (21) is also shown in Figure 1. The shape of the curve changes considerably with temperature, becoming more symmetric for high temperatures. At room temperature, the energy of mixing of the solid solution can be well represented by the expression Ωx(1 – x), with Ω = 0.06–0.02x (in eV/anion), i.e., with a small deviation from the regular solution behavior. As can also be seen in Figure 1, the variation in the entropy of mixing of the alloy with temperature is close to the ideal solution expression – kB[x ln x + (1 – x) ln (1 – x)], which is expected for a random alloy at high temperatures. The variation of the free energy for MAPb(I1–xBrx)3 is shown in Figure 3. For low temperatures the curve is asymmetric around x = 1/2 and is considerably lower in the Br-rich region, a consequence of the existence of the two ordered structures with negative energies of mixing described above. Also for low temperatures the free energy presents points with the same tangent, which indicates the existence of a miscibility gap. As the temperature increases, the shape of the curve becomes more symmetric as the probability of sampling all possible configurations increases.

Figure 3

Figure 3. Calculated Helmholtz free energy as a function of the alloy composition and temperature as calculated within the generalized quasi-chemical approximation.

High Resolution Image
Download MS PowerPoint Slide
Based on the Helmholtz free energy variation, we built the phase diagram of MAPb(I1–xBrx)3, which is shown in Figure 4. The phase diagram reflects the asymmetry of the free energy, showing that the solid solution is more stable in the Br-rich region for typical growth temperatures. The phase diagram also shows that, at 300 K, the alloy is not stable against phase separation in the range of compositions between x1 = 0.19 and x2 = 0.68, the miscibility gap. Under equilibrium conditions, the pure compounds MAPbI3 and MAPbBr3 are not miscible inside this region, and two phases of compositions x1 and x2 must be formed. Also at room temperature, the alloy has spinodal points at the compositions x1′ = 0.28 and x2′ = 0.58, so in the intervals x1 < x < x1′ and x2′ < x < x2 the alloy can present metastable phases, i.e., resistant to small fluctuations in composition. The existence of a miscibility gap at low temperatures is not a surprise, since there is a difference of 6% between the equilibrium lattice constants of MAPbI3 and MAPbBr3. The mismatch of the lattice constants is generally associated with the instability of isovalent solid solutions. (22) The critical temperature–the temperature above which the solid solution is stable for any composition–is 343 K, a value considerably higher than the temperature of 223 K estimated by Yin et al. for the CsPb(I1–xBrx)3 perovskite.
Our model provides a simple thermodynamic explanation for the photoinduced phase separation observed in mixed halide solar cells. In an initial state, a uniform mixture can be fabricated either through control of the deposition kinetics or by annealing above the miscibility temperature. At room temperature, the uniform mixture becomes unstable, but phase separation will be a slow process. Illumination at high light intensities has the effect of overcoming these kinetic barriers and changing the local temperature. Another possible contribution associated with the photocurrent in an active solar cell is electromigration, which will affect Br more than I due to the lower atomic mass.
Direct comparison with experiment is made difficult by the fact that most studies have reported the stoichiometry of the precursor solutions, but not the final materials. Hoke et al. investigated a range of compositions from x = 0 to 1, which were annealed at 373 K. (13) A blue-shift in optical absorption was found from I-rich to Br-rich compositions except for around x = 0.5, which showed a behavior that indicated phase separation into I-rich domains of x ∼ 0.2 from analysis of the spectral shift in photoluminescence. Note that as Br-rich domains will have larger band gaps, they can be spectrally “invisible”. The observed behavior fits very well with our predicted phase diagram (Figure 4). Upon light soaking, compositions of x > 0.2 were all found to exhibit decomposition to the x ∼ 0.2 phase, which from our calculations can be interpreted as the spinodal line at 300 K. A recent investigation by Gil-Escrig of solar cells made from the Br/I mixture show a similar behavior with a marked decrease in performance for Br-rich compositions. The kinetics of these reorganization processes are consistent with the rapid anion exchange observed for these perovskites. (23, 24) Low activation energies for solid-state diffusion have been predicted from simulation studies, (25-27) and there is increasing evidence for mass transport in real devices. (28, 29) While it is unlikely that there is a mechanism to stabilize Br-rich mixtures toward practical devices, compositional engineering—in the three-dimensional Cs1–xMAxPb1–ySnyI3–zBrz system for example—may provide a solution to thermodynamically robust wider band gap materials.

Figure 4

Figure 4. Predicted phase diagram of the MAPb(I1–xBrx)3 alloy. The purple and pink lines are the binodal and spinodal lines, respectively. The dashed horizontal line shows the miscibility gap at room temperature. A thermodynamically stable solid-solution can be formed in the white region only.

High Resolution Image
Download MS PowerPoint Slide
To summarize, we have reported a statistical mechanical study of the solid-solution formed by two halide hybrid perovskites informed by quantum mechanical total energy calculations. The resulting phase diagram for MAPb(I1–xBrx)3 reveals several important features: (i) a critical temperature for mixing of 343 K; (ii) a window between 0.3 < x < 0.6 that is unstable with respect to spinodal decomposition at 300 K; (iii) a binodal (coexistence) point at x = 0.2 and x = 0.7 at 300 K. The thermodynamic metastability of this alloy for intermediate Br/I compositions explains the sensitivity of the mixture to preparatory conditions, temperature, and the operation conditions of a solar cell.

Computational Methods

Click to copy section linkSection link copied!
Disordered materials are challenging to accurately describe using atomistic simulations. We model the halide alloy as a statistical ensemble of independent configurations for seven compositions: x=0,16,13,12,23,56,1. The mixing energy of each configuration with energy Ej is defined as
ΔUj=Ej−(1−x)EMAPbI3−xEMAPbBr3
(1)
where the last two terms represent fractions of the total energy of the pure compounds. The thermodynamic properties of the alloy were determined using the generalized quasi-chemical approximation. (21) This method has been successfully employed in the thermodynamic analysis of semiconductor alloys. (30, 31) By taking into account the total energy and the degeneracy of each configuration, the method provides simple expressions for the mixing contribution to the alloy internal energy ΔU and the configurational entropy ΔS as functions of the composition x and temperature T accordingly to a Boltzmann distribution. With these thermodynamic potentials, the Helmholtz free energy of the alloy can be directly evaluated:
ΔF(x,T)=ΔU(x,T)−TΔS(x,T)
(2)
The phase diagram of the alloy can be built by calculating the free energy at different temperatures. For each temperature, the binodal points are determined by collecting the compositions for which ΔF has a common tangent. The spinodal points are those in which the second derivative of ΔF vanishes. The model has been implemented in a set of Python codes.
The configuration energies Ej were each computed within the framework of Kohn–Sham density functional theory (DFT). (32) We considered a tetragonal supercell with 2 × 1 × 1 expansion of a pseudocubic perovskite building block, which corresponds to six anions. (33, 34) The total number of configurations for this system is 26 = 64. For a perfect inorganic cubic perovskite (Oh symmetry), the three halide sites are equivalent, which reduces the total number of configurations to 21 in total (using the SOD code (35)). Due to the presence of CH3NH3+ cation, the symmetry is formally lowered. As a compromise between computational cost and accuracy, we take the symmetry-reduced inequivalent configurations and perform a full structural relaxation for each case. The initial cells were constructed using a linear combination of the end member lattice constants (a = 6.28 and 5.91 Å for MAPbI3 and MAPbBr3, respectively), i.e. Vegard’s law. As the molecules are known to be rotationally active at room temperature, (36, 37) a range of orientations may be accessible, but this effect is not included in our current model. Contributions from rotational and vibrational entropy are not taken into account in the free energy expansion.
For the DFT total energy calculations, we used the VASP (38) code with the Perdew–Burke–Ernzerhof exchange-correlation functional revised for solids (PBEsol) (39) and the projector augmented-wave formalism (40) including scalar-relativistic corrections. A plane-wave cutoff energy of 500 eV and a 3 × 6 × 6 k-point mesh were used for all the configurations. The lattice volume and shape, and the atomic positions of each configuration were fully optimized to minimize atomic forces below 1.0 meV/Å.
Data Access Statement. The GQCA alloy code is available from https://github.com/WMD-group/GQCA_alloys and the crystal structures from https://github.com/WMD-group/hybrid-perovskites.

Author Information

Click to copy section linkSection link copied!
  • Corresponding Author
    • Aron Walsh - Centre for Sustainable Chemical Technologies and Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom;  Global E3 Institute and Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea;  Email: E-mail: [email protected]
  • Authors
    • Federico Brivio - Centre for Sustainable Chemical Technologies and Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
    • Clovis Caetano - Universidade Federal da Fronteira Sul, Realeza Paraná 85770-000, Brazil
  • Notes
    The authors declare no competing financial interest.

Acknowledgment

Click to copy section linkSection link copied!

The simulations performed in this work benefited from membership of the UK’s HPC Materials Chemistry Consortium, which is funded by EPSRC grant EP/L000202. A.W. is funded by ERC Starting Grant No. 277757, F.B. is supported by EU-FP7 Grant No. 316494, and C.C. acknowledges support from the Brazilian Research Agency CNPq Grant No. 249280/2013-2 PDE.

References

Click to copy section linkSection link copied!

This article references 40 other publications.

  1. 1
    Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S. I. Solvent Engineering for High-performance Inorganic-organic Hybrid Perovskite Solar Cells Nat. Mater. 2014, 13, 897 DOI: 10.1038/nmat4014
    Google Scholar
    1
    Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells
    Jeon, Nam Joong; Noh, Jun Hong; Kim, Young Chan; Yang, Woon Seok; Ryu, Seungchan; Seok, Sang Il
    Nature Materials (2014), 13 (9), 897-903CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    Organolead trihalide perovskite materials have been successfully used as light absorbers in efficient photovoltaic cells. Two different cell structures, based on mesoscopic metal oxides and planar heterojunctions have already demonstrated very impressive advances in performance. Here, we report a bilayer architecture comprising the key features of mesoscopic and planar structures obtained by a fully soln.-based process. We used CH3NH3 Pb(I1 - xBrx)3 (x = 0.1-0.15) as the absorbing layer and poly(triarylamine) as a hole-transporting material. The use of a mixed solvent of γ-butyrolactone and dimethylsulfoxide (DMSO) followed by toluene drop-casting leads to extremely uniform and dense perovskite layers via a CH3NH3I-PbI2-DMSO intermediate phase, and enables the fabrication of remarkably improved solar cells with a certified power-conversion efficiency of 16.2% and no hysteresis. These results provide important progress towards the understanding of the role of soln.-processing in the realization of low-cost and highly efficient perovskite solar cells.
  2. 2
    Zhou, H.; Chen, Q.; Li, G.; Luo, S.; Song, T.-b.; Duan, H.-S.; Hong, Z.; You, J.; Liu, Y.; Yang, Y. Interface Engineering of Highly Efficient Perovskite Solar Cells Science 2014, 345, 542 DOI: 10.1126/science.1254050
    Google Scholar
    2
    Interface engineering of highly efficient perovskite solar cells
    Zhou, Huanping; Chen, Qi; Li, Gang; Luo, Song; Song, Tze-bing; Duan, Hsin-Sheng; Hong, Ziruo; You, Jingbi; Liu, Yongsheng; Yang, Yang
    Science (Washington, DC, United States) (2014), 345 (6196), 542-546CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Advancing perovskite solar cell technologies toward their theor. power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, the authors suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extn. at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on av., with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of the perovskite solar cells was conducted in air and from soln. at low temps., which should simplify manufg. of large-area perovskite devices that are inexpensive and perform at high levels.
  3. 3
    Ahn, N.; Son, D.-Y.; Jang, I.-H.; Kang, S. M.; Choi, M.; Park, N.-G. Highly Reproducible Perovskite Solar Cells with Average Efficiency of 18.3% and Best Efficiency of 19.7% Fabricated via Lewis Base Adduct of Lead(II) Iodide J. Am. Chem. Soc. 2015, 137, 8696 DOI: 10.1021/jacs.5b04930
    Google Scholar
    3
    Highly Reproducible Perovskite Solar Cells with Average Efficiency of 18.3% and Best Efficiency of 19.7% Fabricated via Lewis Base Adduct of Lead(II) Iodide
    Ahn, Namyoung; Son, Dae-Yong; Jang, In-Hyuk; Kang, Seong Min; Choi, Mansoo; Park, Nam-Gyu
    Journal of the American Chemical Society (2015), 137 (27), 8696-8699CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    High efficiency perovskite solar cells were fabricated reproducibly via Lewis base adduct of Pb(II) iodide. PbI2 was dissolved in N,N-dimethyformamide with equimolar N,N-DMSO and CH3NH3I. Stretching vibration of S=O appeared at 1045 cm-1 for bare DMSO, which was shifted to 1020 and 1015 cm-1 upon reacting DMSO with PbI2 and PbI2 + CH3NH3I, resp., indicative of forming the adduct of PbI2·DMSO and CH3NH3I·PbI2·DMSO due to interaction between Lewis base DMSO and/or iodide (I-) and Lewis acid PbI2. Spin-coating of a DMF soln. contg. PbI2, CH3NH3I, and DMSO (1:1:1 mol %) formed a transparent adduct film, which was converted to a dark brown film upon heating at low temp. of 65° for 1 min due to removal of the volatile DMSO from the adduct. The adduct-induced CH3NH3PbI3 exhibited high charge extn. characteristics with hole mobility ≤3.9 × 10-3 cm2/(V s) and slow recombination rate. Av. power conversion efficiency (PCE) of 18.3% was achieved from 41 cells and the best PCE of 19.7% was attained via adduct approach.
  4. 4
    Jeon, N. J.; Noh, J. H.; Yang, W. S.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. Compositional Engineering of Perovskite Materials for High-performance Solar Cells Nature 2015, 517, 476 DOI: 10.1038/nature14133
    Google Scholar
    4
    Compositional engineering of perovskite materials for high-performance solar cells
    Jeon, Nam Joong; Noh, Jun Hong; Yang, Woon Seok; Kim, Young Chan; Ryu, Seungchan; Seo, Jangwon; Seok, Sang Il
    Nature (London, United Kingdom) (2015), 517 (7535), 476-480CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    Here we combine the promising, owing to its comparatively narrow bandgap, but relatively unstable formamidinium lead iodide (FAPbI3) with methylammonium lead bromide (MAPbBr3) as the light-harvesting unit in a bilayer solar cell architecture. We investigated phase stability, morphol. of the perovskite layer, hysteresis in current-voltage characteristics, and overall performance as a function of chem. compn. Our results show that incorporation of MAPbBr3 into FAPbI3 stabilizes the perovskite phase of FAPbI3 and improves the power conversion efficiency of the solar cell to >18% under a std. illumination of 100 mW/cm2. These findings further emphasize the versatility and performance potential of inorg.-org. lead halide perovskite materials for photovoltaic applications.
  5. 5
    Hao, F.; Stoumpos, C. C.; Chang, R. P. H.; Kanatzidis, M. G. Anomalous Band Gap Behavior in Mixed Sn and Pb Perovskites Enables Broadening of Absorption Spectrum in Solar Cells J. Am. Chem. Soc. 2014, 136, 8094 DOI: 10.1021/ja5033259
    Google Scholar
    5
    Anomalous Band Gap Behavior in Mixed Sn and Pb Perovskites Enables Broadening of Absorption Spectrum in Solar Cells
    Hao, Feng; Stoumpos, Constantinos C.; Chang, Robert P. H.; Kanatzidis, Mercouri G.
    Journal of the American Chemical Society (2014), 136 (22), 8094-8099CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Perovskite-based solar cells have recently been catapulted to the cutting edge of thin-film photovoltaic research and development because of their promise for high-power conversion efficiencies and ease of fabrication. Two types of generic perovskites compds. have been used in cell fabrication: either Pb- or Sn-based. Here, we describe the performance of perovskite solar cells based on alloyed perovskite solid solns. of methylammonium tin iodide and its lead analog (CH3NH3Sn1-xPbxI3). We exploit the fact that, the energy band gaps of the mixed Pb/Sn compds. do not follow a linear trend (the Vegard's law) in between these two extremes of 1.55 and 1.35 eV, resp., but have narrower band-gap (<1.3 eV), thus extending the light absorption into the near-IR (∼1,050 nm). A series of soln.-processed solid-state photovoltaic devices using a mixt. of org. spiro-OMeTAD/lithium bis(trifluoromethylsulfonyl)imide/pyridinium additives as hole transport layer were fabricated and studied as a function of Sn to Pb ratio. Our results show that CH3NH3Sn0.5Pb0.5I3 has the broadest light absorption and highest short-circuit photocurrent d. ∼20 mA/cm2 (obtained under simulated full sunlight of 100 mW/cm2).
  6. 6
    Noh, J. H.; Im, S. H.; Heo, J. H.; Mandal, T. N.; Seok, S. I. Chemical Management for Colorful, Efficient, and Stable Inorganic-organic Hybrid Nanostructured Solar Cells Nano Lett. 2013, 13, 1764 DOI: 10.1021/nl400349b
    Google Scholar
    6
    Chemical Management for Colorful, Efficient, and Stable Inorganic-Organic Hybrid Nanostructured Solar Cells
    Noh, Jun Hong; Im, Sang Hyuk; Heo, Jin Hyuck; Mandal, Tarak N.; Seok, Sang Il
    Nano Letters (2013), 13 (4), 1764-1769CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Chem. tuned inorg.-org. hybrid materials, based on MeNH3(=MA)Pb(I1-xBrx)3 perovskites, have been studied using UV-visible absorption and x-ray diffraction patterns and applied to nanostructured solar cells. The band gap engineering brought about by the chem. management of MAPb(I1-xBrx)3 perovskites can be controllably tuned to cover almost the entire visible spectrum, enabling the realization of colorful solar cells. The authors demonstrate highly efficient solar cells exhibiting 12.3% in a power conversion efficiency of under std. AM 1.5, for the most efficient device, as a result of tunable compn. for the light harvester in conjunction with a mesoporous TiO2 film and a hole conducting polymer. Probably the works highlighted in this paper represent one step toward the realization of low-cost, high-efficiency, and long-term stability with colorful solar cells.
  7. 7
    Sadhanala, A.; Deschler, F.; Thomas, T. H.; Dutton, S. E.; Goedel, K. C.; Hanusch, F. C.; Lai, M. L.; Steiner, U.; Bein, T.; Docampo, P. Preparation of Single Phase Films of CH3NH3Pb(I1–xBrx)3 with Sharp Optical Band Edges J. Phys. Chem. Lett. 2014, 5, 2501 DOI: 10.1021/jz501332v
    Google Scholar
    7
    Preparation of Single-Phase Films of CH3NH3Pb(I1-xBrx)3 with Sharp Optical Band Edges
    Sadhanala, Aditya; Deschler, Felix; Thomas, Tudor H.; Dutton, Sian E.; Goedel, Karl C.; Hanusch, Fabian C.; Lai, May L.; Steiner, Ullrich; Bein, Thomas; Docampo, Pablo; Cahen, David; Friend, Richard H.
    Journal of Physical Chemistry Letters (2014), 5 (15), 2501-2505CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    Organometallic lead-halide perovskite-based solar cells now approach 18% efficiency. Introducing a mixt. of bromide and iodide in the halide compn. allows tuning of the optical bandgap. We prep. mixed bromide-iodide lead perovskite films CH3NH3Pb(I1-xBrx)3 (0 ≤ x ≤ 1) by spin-coating from soln. and obtain films with monotonically varying bandgaps across the full compn. range. Photothermal deflection spectroscopy, photoluminescence, and x-ray diffraction show that following suitable fabrication protocols these mixed lead-halide perovskite films form a single phase. The optical absorption edge of the pure tri-iodide and tribromide perovskites is sharp with Urbach energies of 15 and 23 meV, resp., and reaches a max. of 90 meV for CH3NH3PbI1.2Br1.8. We demonstrate a bromide-iodide lead perovskite film (CH3NH3PbI1.2Br1.8) with an optical bandgap of 1.94 eV, which is optimal for tandem cells of these materials with cryst. silicon devices.
  8. 8
    Kulkarni, S. A.; Baikie, T.; Boix, P. P.; Yantara, N.; Mathews, N.; Mhaisalkar, S. Band-gap Tuning of Lead Halide Perovskites Using a Sequential Deposition Process J. Mater. Chem. A 2014, 2, 9221 DOI: 10.1039/C4TA00435C
    Google Scholar
    8
    Band-gap tuning of lead halide perovskites using a sequential deposition process
    Kulkarni, Sneha A.; Baikie, Tom; Boix, Pablo P.; Yantara, Natalia; Mathews, Nripan; Mhaisalkar, Subodh
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2014), 2 (24), 9221-9225CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    Band-gap tuning of mixed anion lead halide perovskites (MAPb(I1-xBrx)2 (0 ≤ x ≤ 1)) has been demonstrated by means of a sequential deposition process. The optical properties of perovskite hybrids can be flexibly modified by changing (mixing) the concn. of halogen precursors. The concns. of precursor soln. as well as the conversion time play an important role in detg. the band-gap of perovskites. A systematic shift of the absorption band edge to shorter wavelengths is obsd. with increasing Br content in the perovskite films, which results in the decrement of the photocurrent. Nanorod like morphol. features are also obsd. for perovskite films with an iodide to bromide molar ratio of <0.7.
  9. 9
    Fedeli, P.; Gazza, F.; Calestani, D.; Ferro, P.; Besagni, T.; Zappettini, A.; Calestani, G.; Marchi, E.; Ceroni, P.; Mosca, R. Influence of the Synthetic Procedures on the Structural and Optical Properties of Mixed-Halide (Br,I) Perovskite Films J. Phys. Chem. C 2015, 119, 21304 DOI: 10.1021/acs.jpcc.5b03923
    Google Scholar
    There is no corresponding record for this reference.
  10. 10
    Ledinský, M.; Löper, P.; Niesen, B.; Holovský, J.; Moon, S.-J.; Yum, J.-H.; De Wolf, S.; Fejfar, A.; Ballif, C. Raman Spectroscopy of Organic Inorganic Halide Perovskites J. Phys. Chem. Lett. 2015, 6, 401 DOI: 10.1021/jz5026323
    Google Scholar
    10
    Raman Spectroscopy of Organic-Inorganic Halide Perovskites
    Ledinsky, Martin; Loper, Philipp; Niesen, Bjoern; Holovsky, Jakub; Moon, Soo-Jin; Yum, Jun-Ho; De Wolf, Stefaan; Fejfar, Antonin; Ballif, Christophe
    Journal of Physical Chemistry Letters (2015), 6 (3), 401-406CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    Micro-Raman spectroscopy provides laterally resolved microstructural information for a broad range of materials. In this Letter, we apply this technique to tri-iodide (CH3NH3PbI3), tribromide (CH3NH3PbBr3), and mixed iodide-bromide (CH3NH3PbI3-xBrx) org.-inorg. halide perovskite thin films and discuss necessary conditions to obtain reliable data. We explain how to measure Raman spectra of pristine CH3NH3PbI3 layers and discuss the distinct Raman bands that develop during moisture-induced degrdn. We also prove unambiguously that the final degrdn. products contain pure PbI2. Moreover, we describe CH3NH3PbI3-xBrx Raman spectra and discuss how the perovskite crystallog. symmetries affect the Raman band intensities and spectral shapes. On the basis of the dependence of the Raman shift on the iodide-to-bromide ratio, we show that Raman spectroscopy is a fast and nondestructive method for the evaluation of the relative iodide-to-bromide ratio.
  11. 11
    Gil-Escrig, L.; Miquel-Sempere, A.; Sessolo, M.; Bolink, H. J. Mixed Iodide-bromide Methylammonium Lead Perovskite-based Diodes for Light Emission and Photovoltaics J. Phys. Chem. Lett. 2015, 6, 3743 DOI: 10.1021/acs.jpclett.5b01716
    Google Scholar
    11
    Mixed Iodide-Bromide Methylammonium Lead Perovskite-based Diodes for Light Emission and Photovoltaics
    Gil-Escrig, Lidon; Miquel-Sempere, Araceli; Sessolo, Michele; Bolink, Henk J.
    Journal of Physical Chemistry Letters (2015), 6 (18), 3743-3748CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    Vacuum deposition techniques are used to prep. mixed iodide-bromide methylammonium lead perovskite diodes via an intermediate double layer of the pure iodide and bromide perovskites. The diodes lead to bright electroluminescence, whose emission spectra maxima shift from the IR toward the visible with increasing bromide content. When illuminated with AM1.5 simulated sunlight the devices function as efficient solar cells with power conversion efficiencies as high as 12.9%.
  12. 12
    Egger, D. A.; Edri, E.; Cahen, D.; Hodes, G. Perovskite Solar Cells: Do We Know What We Do Not Know? J. Phys. Chem. Lett. 2015, 6, 279 DOI: 10.1021/jz502726b
    Google Scholar
    12
    Perovskite Solar Cells: Do We Know What We Do Not Know?
    Egger, David A.; Edri, Eran; Cahen, David; Hodes, Gary
    Journal of Physical Chemistry Letters (2015), 6 (2), 279-282CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    There is no expanded citation for this reference.
  13. 13
    Hoke, E. T.; Slotcavage, D. J.; Dohner, E. R.; Bowring, A. R.; Karunadasa, H. I.; McGehee, M. D. Reversible Photo-induced Trap Formation in Mixed-halide Hybrid Perovskites for Photovoltaics Chem. Sci. 2015, 6, 613 DOI: 10.1039/C4SC03141E
    Google Scholar
    13
    Reversible photo-induced trap formation in mixed-halide hybrid perovskites for photovoltaics
    Hoke, Eric T.; Slotcavage, Daniel J.; Dohner, Emma R.; Bowring, Andrea R.; Karunadasa, Hemamala I.; McGehee, Michael D.
    Chemical Science (2015), 6 (1), 613-617CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    We report on reversible, light-induced transformations in (CH3NH3)Pb(BrxI1-x)3. Photoluminescence (PL) spectra of these perovskites develop a new, red-shifted peak at 1.68 eV that grows in intensity under const., 1-sun illumination in less than a minute. This is accompanied by an increase in sub-bandgap absorption at ∼1.7 eV, indicating the formation of luminescent trap states. Light soaking causes a splitting of X-ray diffraction (XRD) peaks, suggesting segregation into two cryst. phases. Surprisingly, these photo-induced changes are fully reversible; the XRD patterns and the PL and absorption spectra revert to their initial states after the materials are left for a few minutes in the dark. We speculate that photoexcitation may cause halide segregation into iodide-rich minority and bromide-enriched majority domains, the former acting as a recombination center trap. This instability may limit achievable voltages from some mixed-halide perovskite solar cells and could have implications for the photostability of halide perovskites used in optoelectronics.
  14. 14
    Niemann, R. G.; Kontos, A. G.; Palles, D.; Kamitsos, E. I.; Kaltzoglou, A.; Brivio, F.; Falaras, P.; Cameron, P. J. Halogen Effects on Ordering and Bonding of CH3NH3+ in CH3NH3PbX3 (X= Cl, Br, I) Hybrid Perovskites: A Vibrational Spectroscopic Study J. Phys. Chem. C 2016, 120, 2509 DOI: 10.1021/acs.jpcc.5b11256
    Google Scholar
    14
    Halogen Effects on Ordering and Bonding of CH3NH3+ in CH3NH3PbX3 (X = Cl, Br, I) Hybrid Perovskites: A Vibrational Spectroscopic Study
    Niemann, Ralf G.; Kontos, Athanassios G.; Palles, Dimitrios; Kamitsos, Efstratios I.; Kaltzoglou, Andreas; Brivio, Federico; Falaras, Polycarpos; Cameron, Petra J.
    Journal of Physical Chemistry C (2016), 120 (5), 2509-2519CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    This study reports Raman and IR spectra of hybrid org.-inorg. MAPbX3 perovskites (MA = CH3NH3, X = Cl, Br, I) and their mixed-halide derivs. Raman spectra were recorded at three laser wavelengths (514, 785, and 1064 nm) under on- and off-resonance conditions, as well as at room temp. and 100 K. The use of different excitation wavelengths allowed the unambiguous acquisition of "true" Raman spectra from the perovskites, without degrdn. or photoinduced structural changes. Low-frequency PbX vibrational modes were thoroughly identified by comparison of Raman and far-IR results. Red Raman frequency shifts for almost all MA vibrations from 200 to 3200 cm-1, and particularly intense for the torsional mode, were obsd. toward heavy halide derivs., indicative of strengthening the interaction between halides and the org. cation inside the inorg. cage. Different MA-X bonding schemes are evidenced by torsional mode pairs emerging in the orthorhombic phase. MAPbBr3 was further characterized by variable temp. Raman measurements (100-295 K). Broadening of the MA rocking mode slightly above the tetragonal I to II phase transition is connected with disorder of the MA cation. Our results advance the understanding of perovksite materials properties (ferroelec. domain formation, anomalous hysteresis) and their use as efficient light absorbers in solar cells.
  15. 15
    Xiao, Z.; Yuan, Y.; Shao, Y.; Wang, Q.; Dong, Q.; Bi, C.; Sharma, P.; Gruverman, A.; Huang, J. Giant Switchable Photovoltaic Effect in Organometal Trihalide Perovskite Devices Nat. Mater. 2015, 14, 193 DOI: 10.1038/nmat4150
    Google Scholar
    15
    Giant switchable photovoltaic effect in organometal trihalide perovskite devices
    Xiao, Zhengguo; Yuan, Yongbo; Shao, Yuchuan; Wang, Qi; Dong, Qingfeng; Bi, Cheng; Sharma, Pankaj; Gruverman, Alexei; Huang, Jinsong
    Nature Materials (2015), 14 (2), 193-198CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    Organolead trihalide perovskite (OTP) materials are emerging as naturally abundant materials for low-cost, soln.-processed and highly efficient solar cells. Here, we show that, in OTP-based photovoltaic devices with vertical and lateral cell configurations, the photocurrent direction can be switched repeatedly by applying a small elec. field of <1 V μm-1. The switchable photocurrent, generally obsd. in devices based on ferroelec. materials, reached 20.1 mA cm-2 under one sun illumination in OTP devices with a vertical architecture, which is four orders of magnitude larger than that measured in other ferroelec. photovoltaic devices. This field-switchable photovoltaic effect can be explained by the formation of reversible p-i-n structures induced by ion drift in the perovskite layer. The demonstration of switchable OTP photovoltaics and elec.-field-manipulated doping paves the way for innovative solar cell designs and for the exploitation of OTP materials in elec. and optically readable memristors and circuits.
  16. 16
    Yuan, Y.; Huang, J. Ion Migration in Organometal Trihalide Perovskite and Its Impact on Photovoltaic Efficiency and Stability Acc. Chem. Res. 2016, 49, 286 DOI: 10.1021/acs.accounts.5b00420
    Google Scholar
    16
    Ion Migration in Organometal Trihalide Perovskite and Its Impact on Photovoltaic Efficiency and Stability
    Yuan, Yongbo; Huang, Jinsong
    Accounts of Chemical Research (2016), 49 (2), 286-293CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    A review. Organometal trihalide perovskites (OTPs) are emerging as very promising photovoltaic materials because the power conversion efficiency (PCE) of OTP solar cells quickly rises and now rivals with that of single crystal silicon solar cells after only five-years research. Their prospects to replace silicon photovoltaics to reduce the cost of renewable clean energy are boosted by the low-temp. soln. processing as well as the very low-cost raw materials and relative insensitivity to defects. The flexibility, semitransparency, and vivid colors of perovskite solar cells are attractive for niche applications such as built-in photovoltaics and portable lightwt. chargers. However, the low stability of current hybrid perovskite solar cells remains a serious issue to be solved before their broad application. Among all those factors that affect the stability of perovskite solar cells, ion migration in OTPs may be intrinsic and cannot be taken away by device encapsulation.The presence of ion migration has received broad attention after the report of photocurrent hysteresis in OTP based solar cells. As suggested by much direct and indirect exptl. evidence, the ion migration is speculated to be the origin or an important contributing factor for many obsd. unusual phenomenon in OTP materials and devices, such as current-voltage hysteresis, switchable photovoltaic effect, giant dielec. const., diminished transistor behavior at room temp., photoinduced phase sepn., photoinduced self-poling effect, and elec.-field driven reversible conversion between lead iodide (PbI2) and methylammonium lead triiodide (MAPbI3). Undoubtedly thorough insight into the ion-migration mechanism is highly desired for the development of OTP based devices to improve intrinsic stability in the dark and under illumination. In this Account, we critically review the recent progress in understanding the fundamental science on ion migration in OTP based solar cells. We look into both theor. and expt. advances in answering these basic questions: Does ion migration occur and cause the photocurrent hysteresis in perovskite solar cells. What are the migrating ion species. How do ions migrate. How does ion migration impact the device efficiency and stability. How can ion migration be mitigated or eliminated. We also raise some questions that need to be understood and addressed in the future.
  17. 17
    Mosconi, E.; Amat, A.; Nazeeruddin, M. K.; Grätzel, M.; De Angelis, F. First Principles Modeling of Mixed Halde Organometal Perovskites for Photovoltaic Applications J. Phys. Chem. C 2013, 117, 13902 DOI: 10.1021/jp4048659
    Google Scholar
    There is no corresponding record for this reference.
  18. 18
    Yin, W.-J.; Yan, Y.; Wei, S.-H. Anomalous Alloy Properties in Mixed Halide Perovskites J. Phys. Chem. Lett. 2014, 5, 3625 DOI: 10.1021/jz501896w
    Google Scholar
    18
    Anomalous Alloy Properties in Mixed Halide Perovskites
    Yin, Wan-Jian; Yan, Yanfa; Wei, Su-Huai
    Journal of Physical Chemistry Letters (2014), 5 (21), 3625-3631CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    Engineering halide perovskite through mixing halogen elements, such as CH3NH3PbI3-xClx and CH3NH3PbI3-xBrx, is a viable way to tune its electronic and optical properties. Despite many emerging expts. on mixed halide perovskites, the basic electronic and structural properties of the alloys were not understood and some crucial questions remain, for example, how much Cl can be incorporated into CH3NH3PbI3 is still unclear. In this Letter, the authors chose CsPbX3 (X = I, Br, Cl) as an example and use a 1st-principle calcn. together with cluster-expansion methods to systematically study the structural, electronic, and optical properties of mixed halide perovskites and find that unlike conventional semiconductor alloys, they exhibit many anomalous alloy properties such as small or even neg. formation energies at some concns. and negligible or even neg. band gap bowing parameters at high temp. Further mixed-(I,Cl) perovskite is hard to form at temp. <625 K, whereas forming mixed-(Br,Cl) and (I,Br) alloys are easy at room temp.
  19. 19
    Onoda-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 DOI: 10.1016/0022-3697(90)90021-7
    Google Scholar
    19
    Calorimetric and IR spectroscopic studies of phase transitions in methylammonium trihaloplumbates(II)
    Onoda-Yamamuro, Noriko; Matsuo, Takasuke; Suga, Hiroshi
    Journal 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.
  20. 20
    Shannon, R. D. Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32, 751 DOI: 10.1107/S0567739476001551
    Google Scholar
    There is no corresponding record for this reference.
  21. 21
    Sher, A.; van Schilfgaarde, M.; Chen, A.-B.; Chen, W. Quasichemical Approximation in Binary Alloys Phys. Rev. B: Condens. Matter Mater. Phys. 1987, 36, 4279 DOI: 10.1103/PhysRevB.36.4279
    Google Scholar
    There is no corresponding record for this reference.
  22. 22
    Stringfellow, G. Calculation of Ternary and Quaternary III-V Phase Diagrams J. Cryst. Growth 1974, 27, 21 DOI: 10.1016/S0022-0248(74)80047-3
    Google Scholar
    22
    Calculation of ternary and quaternary III-V phase diagrams
    Stringfellow, G. B.
    Journal of Crystal Growth (1974), 27 (), 21-34CODEN: JCRGAE; ISSN:0022-0248.
    The models used to calc. binary and ternary III-V phase diagrams are reviewed. The simple solns. moel with Ω = a - bT is found to satisfactorily describe the liq. phase and the solid phase is adequately described using the regular soln. model. The DLP (delta lattice parameter) model of the solid, based on the concept that the bonding in alloys is detd. largely by the energy of the electrons, is found to be capable of predicting accurately the magnitudes of the solid interaction parameters knowing only the lattice parameters of the pure III-V compds. The simple soln. model with Ω = a - βT for the liq. and DLP model for the solid is then used in the calcn. of the quaternary III-V phase diagrams. One outcome of the calcn. is the establishment of a condition which can be used to check the consistency of the parameters ΔHF, TF, and Ω1 of the four solid III-V compds. bounding the solid phase field, against the soln. model. The agreement of the calcd. quaternary results with expt. in the GaxIn1-xAs1-y system is satisfactory. In the AlxGa1-xPyAs1-y system, the consistency condition is not satisfied, and thus the calcn. cannot agree with previous ternary calcns. for the (Al,Ga)As, (Al,Ga)P and Ga(As,P) systems simultaneously. Parameters were chosen so that good agreement is established with all except the (Al,Ga)P ternary.
  23. 23
    Yang, T.-Y.; Gregori, G.; Pellet, N.; Grätzel, M.; Maier, J. The Significance of Ion Conduction in a Hybrid Organic-Inorganic Lead-Iodide-Based Perovskite Photosensitizer Angew. Chem., Int. Ed. 2015, 54, 7905 DOI: 10.1002/anie.201500014
    Google Scholar
    23
    The Significance of Ion Conduction in a Hybrid Organic-Inorganic Lead Iodide-Based Perovskite Photosensitizer
    Yang, Tae-Youl; Gregori, Giuliano; Pellet, Norman; Graetzel, Michael; Maier, Joachim
    Angewandte Chemie, International Edition (2015), 54 (27), 7905-7910CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The success of perovskite solar cells has sparked excitement in the photovoltaic community not only because of unexpectedly high efficiencies but also because of the future potential ascribed to such cryst. absorber materials. Far from being exhaustively studied in terms of solid-state properties, these materials surprised by anomalies such as a huge apparent low-frequency dielec. const. and pronounced hysteretic current-voltage behavior. Methylammonium (but also formamidinium) iodoplumbates are mixed conductors with a large fraction of ion conduction because of I ions. In particular, the authors measure and model the stoichiometric polarization caused by the mixed conduction and demonstrate that the above anomalies can be explained by the build-up of stoichiometric gradients as a consequence of ion blocking interfaces. These findings provide insight into elec. charge transport in the hybrid org.-inorg. lead halide solar cells as well as into new possibilities of improving the photovoltaic performance by controlling the ionic disorder.
  24. 24
    Zhang, Y.; Liu, M.; Eperon, G. E.; Leijtens, T. C.; McMeekin, D.; Saliba, M.; Zhang, W.; De Bastiani, M.; Petrozza, A.; Herz, L. M. Charge Selective Contacts, Mobile Ions and Anomalous Hysteresis in Organic-Inorganic Perovskite Solar Cells Mater. Horiz. 2015, 2, 315 DOI: 10.1039/C4MH00238E
    Google Scholar
    24
    Charge selective contacts, mobile ions and anomalous hysteresis in organic-inorganic perovskite solar cells
    Zhang, Ye; Liu, Mingzhen; Eperon, Giles E.; Leijtens, Tomas C.; McMeekin, David; Saliba, Michael; Zhang, Wei; de Bastiani, Michele; Petrozza, Annamaria; Herz, Laura M.; Johnston, Michael B.; Lin, Hong; Snaith, Henry J.
    Materials Horizons (2015), 2 (3), 315-322CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
    High-efficiency perovskite solar cells typically employ an org.-inorg. metal halide perovskite material as light absorber and charge transporter, sandwiched between a p-type electron-blocking org. hole-transporting layer and an n-type hole-blocking electron collection titania compact layer. Some device configurations also include a thin mesoporous layer of TiO2 or Al2O3 which is infiltrated and capped with the perovskite absorber. Herein, we demonstrate that it is possible to fabricate planar and mesoporous perovskite solar cells devoid of an electron selective hole-blocking titania compact layer, which momentarily exhibit power conversion efficiencies (PCEs) of over 13%. This performance is however not sustained and is related to the previously obsd. anomalous hysteresis in perovskite solar cells. The "compact layer-free" meso-superstructured perovskite devices yield a stabilized PCE of only 2.7% while the compact layer-free planar heterojunction devices display no measurable steady state power output when devoid of an electron selective contact. In contrast, devices including the titania compact layer exhibit stabilized efficiency close to that derived from the current voltage measurements. We propose that under forward bias the perovskite diode becomes polarised, providing a beneficial field, allowing accumulation of pos. and neg. space charge near the contacts, which enables more efficient charge extn. This provides the required built-in potential and selective charge extn. at each contact to temporarily enable efficient operation of the perovskite solar cells even in the absence of charge selective n- and p-type contact layers. The polarisation of the material is consistent with long range migration and accumulation of ionic species within the perovskite to the regions near the contacts. When the external field is reduced under working conditions, the ions can slowly diffuse away from the contacts redistributing throughout the film, reducing the field asymmetry and the effectiveness of the operation of the solar cells. We note that in light of recent publications showing high efficiency in devices devoid of charge. selective contacts, this work reaffirms the abs. necessity to measure and report the stabilized power output under load when characterizing perovskite solar cells.
  25. 25
    Eames, C.; Frost, J. M.; Barnes, P. R. F.; O’Regan, B. C.; Walsh, A.; Islam, M. S. Ionic Transport in Hybrid Lead Iodide Perovskite Solar Cells Nat. Commun. 2015, 6, 7497 DOI: 10.1038/ncomms8497
    Google Scholar
    25
    Ionic transport in hybrid lead iodide perovskite solar cells
    Eames, Christopher; Frost, Jarvist M.; Barnes, Piers R. F.; O'Regan, Brian C.; Walsh, Aron; Islam, M. Saiful
    Nature Communications (2015), 6 (), 7497CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    Solar cells based on org.-inorg. halide perovskites have recently shown rapidly rising power conversion efficiencies, but exhibit unusual behavior such as current-voltage hysteresis and a low-frequency giant dielec. response. Ionic transport has been suggested to be an important factor contributing to these effects; however, the chem. origin of this transport and the mobile species are unclear. Here, the activation energies for ionic migration in methylammonium lead iodide (CH3NH3PbI3) are derived from first principles, and are compared with kinetic data extd. from the current-voltage response of a perovskite-based solar cell. We identify the microscopic transport mechanisms, and find facile vacancy-assisted migration of iodide ions with an activation energy of 0.6 eV, in good agreement with the kinetic measurements. The results of this combined computational and exptl. study suggest that hybrid halide perovskites are mixed ionic-electronic conductors, a finding that has major implications for solar cell device architectures.
  26. 26
    Haruyama, J.; Sodeyama, K.; Han, L.; Tateyama, Y. First-Principles Study of Ion Diffusion in Perovskite Solar Cell Sensitizers J. Am. Chem. Soc. 2015, 137, 10048 DOI: 10.1021/jacs.5b03615
    Google Scholar
    26
    First-Principles Study of Ion Diffusion in Perovskite Solar Cell Sensitizers
    Haruyama, Jun; Sodeyama, Keitaro; Han, Liyuan; Tateyama, Yoshitaka
    Journal of the American Chemical Society (2015), 137 (32), 10048-10051CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Hysteresis in current-voltage curves has been an important issue for conversion efficiency evaluation and development of perovskite solar cells (PSCs). In this study, we explored the ion diffusion effects in tetragonal CH3NH3PbI3 (MAPbI3) and trigonal (NH2)2CHPbI3 (FAPbI3) by first-principles calcns. The calcd. activation energies of the anionic and cationic vacancy migrations clearly show that I- anions in both MAPbI3 and FAPbI3 can easily diffuse with low barriers of ca. 0.45 eV, comparable to that obsd. in ion-conducting materials. More interestingly, typical MA+ cations and larger FA+ cations both have rather low barriers as well, indicating that the cation mols. can migrate in the perovskite sensitizers when a bias voltage is applied. These results can explain the ion displacement scenario recently proposed by expts. With the dil. diffusion theory, we discuss that smaller vacancy concns. (higher crystallinity) and replacement of MA+ with larger cation mols. will be essential for suppressing hysteresis as well as preventing aging behavior of PSC photosensitizers.
  27. 27
    Azpiroz, J. M.; Mosconi, E.; Bisquert, J.; De Angelis, F. Defects Migration in Methylammonium Lead Iodide and their Role in Perovskite Solar Cells Operation Energy Environ. Sci. 2015, 8, 2118 DOI: 10.1039/C5EE01265A
    Google Scholar
    27
    Defect migration in methylammonium lead iodide and its role in perovskite solar cell operation
    Azpiroz, Jon M.; Mosconi, Edoardo; Bisquert, Juan; De Angelis, Filippo
    Energy & Environmental Science (2015), 8 (7), 2118-2127CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
    In spite of the unprecedented advance of organohalide lead perovskites in the photovoltaics scenario, many of the characteristics of this class of materials, including their slow photocond. response, solar cell hysteresis, and switchable photocurrent, remain poorly understood. Many exptl. hints point to defect migration as a plausible mechanism underlying these anomalous properties. By means of state-of-the-art first-principles computational analyses carried out on the tetragonal MAPbI3 (MA = methylammonium) perovskite and on its interface with TiO2, we demonstrate that iodine vacancies and interstitials may easily diffuse across the perovskite crystal, with migration activation energies as low as ∼0.1 eV. Under working conditions, iodine-related defects are predicted to migrate at the electrodes on very short time scales (<1 μs). MA and Pb vacancies, with calcd. activation barriers of ∼0.5 and 0.8 eV, resp., could be responsible for the slow response inherent to perovskites, with typical calcd. migration times of the order of tens of ms to minutes. By investigating realistic models of the perovskite/TiO2 interface we show that neg. charged defects, e.g. MA vacancies, close to the electron transport layer (TiO2 in our case) modify the perovskite electronic state landscape, hampering charge extn. at selective contacts, thus possibly contributing to the obsd. solar cell hysteresis. We further demonstrate the role of the electron transport layer in affecting the initial concn. of defects close to the selective contacts, highlighting how charge sepn. at the perovskite/TiO2 interface may further change the defect distribution. We believe that this work, identifying the mobile species in perovskite solar cells, their migration across the perovskite material, and their effect on the operational mechanism of the device, may pave the way for the development of new materials and solar cell architectures with improved and stabilized efficiencies.
  28. 28
    Hentz, O.; Zhao, Z.; Gradecak, S. Impacts of Ion Segregation on Local Optical Properties in Mixed Halide Perovskite Films Nano Lett. 2016, 16, 1485 DOI: 10.1021/acs.nanolett.5b05181
    Google Scholar
    28
    Impacts of Ion Segregation on Local Optical Properties in Mixed Halide Perovskite Films
    Hentz, Olivia; Zhao, Zhibo; Gradecak, Silvija
    Nano Letters (2016), 16 (2), 1485-1490CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Despite the recent astronomical success of org.-inorg. perovskite solar cells (PSCs), the impact of microscale film inhomogeneities on device performance remains poorly understood. In this work, we study CH3NH3PbI3 perovskite films using cathodoluminescence in scanning transmission electron microscopy and show that localized regions with increased cathodoluminescence intensity correspond to iodide-enriched regions. These observations constitute direct evidence that nanoscale stoichiometric variations produce corresponding inhomogeneities in film cathodoluminescence intensity. Moreover, we observe the emergence of high-energy transitions attributed to beam induced iodide segregation, which may mirror the effects of ion migration during PSC operation. Our results demonstrate that such ion segregation can fundamentally change the local optical and microstructural properties of org.-inorg. perovskite films in the course of normal device operation and therefore address the obsd. complex and unpredictable behavior in PSC devices.
  29. 29
    Shi, J.; Xu, X.; Zhang, H.; Luo, Y.; Li, D.; Meng, Q. Intrinsic Slow Charge Response in the Perovskite Solar Cells: Electron and Ion Transport Appl. Phys. Lett. 2015, 107, 163901 DOI: 10.1063/1.4934633
    Google Scholar
    There is no corresponding record for this reference.
  30. 30
    Teles, L. K.; Furthmüller, J.; Scolfaro, L. M. R.; Leite, J. R.; Bechstedt, F. First-principles Calculations of the Thermodynamic and Structural Properties of Strained InxGa1–xN and AlxGa1–xN Alloys Phys. Rev. B: Condens. Matter Mater. Phys. 2000, 62, 2475 DOI: 10.1103/PhysRevB.62.2475
    Google Scholar
    30
    First-principles calculations of the thermodynamic and structural properties of strained InxGa1-xN and AlxGa1-xN alloys
    Teles, L. K.; Furthmuller, J.; Scolfaro, L. M. R.; Leite, J. R.; Bechstedt, F.
    Physical Review B: Condensed Matter and Materials Physics (2000), 62 (4), 2475-2485CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
    We present first-principles calcns. of the thermodn. and structural properties of cubic InxGa1-xN and AlxGa1-xN alloys. They are based on the generalized quasi-chem. approach to disorder and compn. effects and a pseudopotential-plane-wave approxn. for the total energy. The cluster treatment is generalized to study the influence of biaxial strain. We find a remarkable suppression of phase sepn. in InxGa1-xN.
  31. 31
    Schleife, A.; Eisenacher, M.; Rödl, C.; Fuchs, F.; Furthmüller, J.; Bechstedt, F. Ab initio Description of Heterostructural Alloys: Thermodynamic and Structural Properties of MgxZn1–xO and CdxZn1–xO Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 81, 245210 DOI: 10.1103/PhysRevB.81.245210
    Google Scholar
    There is no corresponding record for this reference.
  32. 32
    Kohn, W.; Sham, L. J. Self-consistent Equations Including Exchange and Correlation Effects Phys. Rev. 1965, 140, A1133 DOI: 10.1103/PhysRev.140.A1133
    Google Scholar
    There is no corresponding record for this reference.
  33. 33
    Frost, J. M.; Butler, K. T.; Brivio, F.; Hendon, C. H.; van Schilfgaarde, M.; Walsh, A. Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells Nano Lett. 2014, 14, 2584 DOI: 10.1021/nl500390f
    Google Scholar
    33
    Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells
    Frost, Jarvist M.; Butler, Keith T.; Brivio, Federico; Hendon, Christopher H.; van Schilfgaarde, Mark; Walsh, Aron
    Nano Letters (2014), 14 (5), 2584-2590CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    The performance of organometallic perovskite solar cells has rapidly surpassed that of both conventional dye-sensitized and org. photovoltaics. High-power conversion efficiency can be realized in both mesoporous and thin-film device architectures. The authors address the origin of this success in the context of the materials chem. and physics of the bulk perovskite as described by electronic structure calcns. In addn. to the basic optoelectronic properties essential for an efficient photovoltaic device (spectrally suitable band gap, high optical absorption, low carrier effective masses), the materials are structurally and compositionally flexible. As the authors show, hybrid perovskites exhibit spontaneous elec. polarization; the authors also suggest ways in which this can be tuned through judicious choice of the org. cation. The presence of ferroelec. domains will result in internal junctions that may aid sepn. of photoexcited electron and hole pairs, and redn. of recombination through segregation of charge carriers. The combination of high dielec. const. and low effective mass promotes both Wannier-Mott exciton sepn. and effective ionization of donor and acceptor defects. The photoferroic effect could be exploited in nanostructured films to generate a higher open circuit voltage and may contribute to the current-voltage hysteresis obsd. in perovskite solar cells.
  34. 34
    Brivio, F.; Frost, J. M.; Skelton, J. M.; Jackson, A. J.; Weber, O. J.; Weller, M. T.; Goni, A. R.; Leguy, A. M. A.; Barnes, P. R. F.; Walsh, A. Lattice Dynamics and Vibrational Spectra of the Orthorhombic, Tetragonal, and Cubic Phases of Methylammonium Lead Iodide Phys. Rev. B: Condens. Matter Mater. Phys. 2015, 92, 144308 DOI: 10.1103/PhysRevB.92.144308
    Google Scholar
    34
    Lattice dynamics and vibrational spectra of the orthorhombic, tetragonal, and cubic phases of methylammonium lead iodide
    Brivio, Federico; Frost, Jarvist M.; Skelton, Jonathan M.; Jackson, Adam J.; Weber, Oliver J.; Weller, Mark T.; Goni, Alejandro R.; Leguy, Aurelien M. A.; Barnes, Piers R. F.; Walsh, Aron
    Physical Review B: Condensed Matter and Materials Physics (2015), 92 (14), 144308/1-144308/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    The hybrid halide perovskite CH3NH3PbI3 exhibits a complex structural behavior, with successive transitions between orthorhombic, tetragonal, and cubic polymorphs around 165 and 327 K. Herein we report first-principles lattice dynamics (phonon spectrum) for each phase of CH3NH3PbI3. The equil. structures compare well to solns. of temp.-dependent powder neutron diffraction. By following the normal modes, we calc. IR and Raman intensities of the vibrations, and compare them to the measurement of a single crystal where the Raman laser is controlled to avoid degrdn. of the sample. Despite a clear sepn. in energy between low-frequency modes assocd. with the inorg. (PbI3-)n network and high-frequency modes of the org. CH3NH3+ cation, significant coupling between them is found, which emphasizes the interplay between mol. orientation and the corner-sharing octahedral networks in the structural transformations. Soft modes are found at the boundary of the Brillouin zone of the cubic phase, consistent with displacive instabilities and anharmonicity involving tilting of the PbI6 octahedra around room temp.
  35. 35
    Grau-Crespo, R.; Hamad, S.; Catlow, C. R. A.; de Leeuw, N. H. Symmetry-adapted Configurational Modelling of Fractional Site Occupancy in Solids J. Phys.: Condens. Matter 2007, 19, 256201 DOI: 10.1088/0953-8984/19/25/256201
    Google Scholar
    35
    Symmetry-adapted configurational modelling of fractional site occupancy in solids
    Grau-Crespo, R.; Hamad, S.; Catlow, C. R. A.; de Leeuw, N. H.
    Journal of Physics: Condensed Matter (2007), 19 (25), 256201/1-256201/16CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)
    A methodol. is presented, which reduces the no. of site-occupancy configurations to be calcd. when modeling site disorder in solids, by taking advantage of the crystal symmetry of the lattice. Within this approach, two configurations are considered equiv. when they are related by an isometric operation; a trial list of possible isometric transformations is provided by the group of symmetry operators in the parent structure, which is used to generate all configurations via at. substitutions. We have adapted the equations for configurational statistics to operate in the reduced configurational space of the independent configurations. Each configuration in this space is characterized by its reduced energy, which includes not only its energy but also a contribution from its degeneracy in the complete configurational space, via an entropic term. The new computer program SOD (site-occupancy disorder) is presented, which performs this anal. in systems with arbitrary symmetry and any size of supercell. As a case study we use the distribution of cations in iron antimony oxide FeSbO4, where we also introduce some general considerations for the modeling of site-occupancy disorder in paramagnetic systems.
  36. 36
    Leguy, A.; Hu, Y.; Campoy-Quiles, M.; Alonso, M. I.; Weber, O. J.; Azarhoosh, P.; van Schilfgaarde, M.; Weller, M. T.; Bein, T.; Nelson, J. The Reversible Hydration of CH3NH3PbI3 in Films, Single Crystals and Solar Cells Chem. Mater. 2015, 27, 3397 DOI: 10.1021/acs.chemmater.5b00660
    Google Scholar
    36
    Reversible Hydration of CH3NH3PbI3 in Films, Single Crystals, and Solar Cells
    Leguy, Aurelien M. A.; Hu, Yinghong; Campoy-Quiles, Mariano; Alonso, M. Isabel; Weber, Oliver J.; Azarhoosh, Pooya; van Schilfgaarde, Mark; Weller, Mark T.; Bein, Thomas; Nelson, Jenny; Docampo, Pablo; Barnes, Piers R. F.
    Chemistry of Materials (2015), 27 (9), 3397-3407CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Solar cells composed of methylammonium lead iodide perovskite (MAPI) are notorious for their sensitivity to moisture. It is shown that hydrated crystal phases are formed when MAPI is exposed to water vapor at room temp. and these phase changes are fully reversed when the material is subsequently dried. The reversible formation of CH3NH3PbI3·H2O followed by (CH3NH3)4PbI6·2H2O (upon long exposure times) was obsd. using time-resolved XRD and ellipsometry of thin films prepd. using "solvent engineering", single crystals, and state-of-the-art solar cells. In contrast to water vapor, the presence of liq. water results in the irreversible decompn. of MAPI to form PbI2. MAPI changes from dark brown to transparent on hydration; the precise optical consts. of CH3NH3PbI3·H2O formed on single crystals were detd., with a bandgap at 3.1 eV. Using the single-crystal optical consts. and thin-film ellipsometry measurements, the time-dependent changes to MAPI films exposed to moisture were modeled. The results suggest that the monohydrate phase forms independent of the depth in the film, suggesting rapid transport of water mols. along grain boundaries. Vapor-phase hydration of an unencapsulated solar cell (initially Jsc ≈ 19 mA cm-2 and Voc ≈ 1.05 V at 1 sun) resulted in more than a 90% drop in short-circuit photocurrent and ∼200 mV loss in open-circuit potential; however, these losses were fully reversed after the device was exposed to dry nitrogen for 6 h. Hysteresis in the current-voltage characteristics was significantly increased after this dehydration, which may be related to changes in the defect d. and morphol. of MAPI following recrystn. from the hydrate. Based on the observations, it is suggested that irreversible decompn. of MAPI in the presence of water vapor only occurs significantly once a grain has been fully converted to the monohydrate phase.
  37. 37
    Bakulin, A. A.; Selig, O.; Bakker, H. J.; Rezus, Y. L. A.; Müller, C.; Glaser, T.; Lovrincic, R.; Sun, Z.; Chen, Z.; Walsh, A. Real-Time Observation of Organic Cation Reorientation in Methylammonium Lead Iodide Perovskites J. Phys. Chem. Lett. 2015, 6, 3663 DOI: 10.1021/acs.jpclett.5b01555
    Google Scholar
    37
    Real-Time Observation of Organic Cation Reorientation in Methylammonium Lead Iodide Perovskites
    Bakulin, Artem A.; Selig, Oleg; Bakker, Huib J.; Rezus, Yves L. A.; Mueller, Christian; Glaser, Tobias; Lovrincic, Robert; Sun, Zhenhua; Chen, Zhuoying; Walsh, Aron; Frost, Jarvist M.; Jansen, Thomas L. C.
    Journal of Physical Chemistry Letters (2015), 6 (18), 3663-3669CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    The introduction of a mobile and polarized org. moiety as a cation in 3D Pb-iodide perovskites brings fascinating optoelectronic properties to these materials. The extent and the time scales of the orientational mobility of the org. cation and the mol. mechanism behind its motion remain unclear, with different exptl. and computational approaches providing very different qual. and quant. description of the mol. dynamics. Ultrafast 2D vibrational spectroscopy of methylammonium (MA) Pb iodide was used to directly resolve the rotation of the org. cations within the MAPbI3 lattice. The results reveal 2 characteristic time consts. of motion. Using ab initio mol. dynamics simulations, the authors identify these as a fast (∼300 fs) wobbling-in-a-cone motion around the crystal axis and a relatively slow (∼3 ps) jump-like reorientation of the mol. dipole with respect to the iodide lattice. The obsd. dynamics are essential for understanding the electronic properties of perovskite materials.
  38. 38
    Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab initio Total-energy Calculations Using a Plane-wave Basis Set Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169 DOI: 10.1103/PhysRevB.54.11169
    Google Scholar
    38
    Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set
    Kresse, G.; Furthmueller, J.
    Physical Review B: Condensed Matter (1996), 54 (16), 11169-11186CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
    The authors present an efficient scheme for calcg. the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrixes will be discussed. This approach is stable, reliable, and minimizes the no. of order Natoms3 operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special "metric" and a special "preconditioning" optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calcns. It will be shown that the no. of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order Natoms2 scaling is found for systems contg. up to 1000 electrons. If we take into account that the no. of k points can be decreased linearly with the system size, the overall scaling can approach Natoms. They have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable.
  39. 39
    Perdew, J. P.; Ruzsinszky, A.; Csonka, G. I.; Vydrov, O. A.; Scuseria, G. E.; Constantin, L. A.; Zhou, X.; Burke, K. Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces Phys. Rev. Lett. 2008, 100, 136406 DOI: 10.1103/PhysRevLett.100.136406
    Google Scholar
    39
    Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces
    Perdew, John P.; Ruzsinszky, Adrienn; Csonka, Gabor I.; Vydrov, Oleg A.; Scuseria, Gustavo E.; Constantin, Lucian A.; Zhou, Xiaolan; Burke, Kieron
    Physical Review Letters (2008), 100 (13), 136406/1-136406/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    Popular modern generalized gradient approxns. are biased toward the description of free-atom energies. Restoration of the first-principles gradient expansion for exchange over a wide range of d. gradients eliminates this bias. We introduce a revised Perdew-Burke-Ernzerhof generalized gradient approxn. that improves equil. properties of densely packed solids and their surfaces.
  40. 40
    Blöchl, P. E. Projector Augmented-wave Method Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 50, 17953 DOI: 10.1103/PhysRevB.50.17953
    Google Scholar
    40
    Projector augmented-wave method
    Blochl
    Physical review. B, Condensed matter (1994), 50 (24), 17953-17979 ISSN:0163-1829.
    There is no expanded citation for this reference.

Cited By

Click to copy section linkSection link copied!
Citation Statements
Explore this article's citation statements on scite.ai
powered by  Scite

This article is cited by 341 publications.

  1. Arup Ghorai, Sudarshan Singh, Baidyanath Roy, Shaona Bose, Somnath Mahato, Nikolai Mukhin, Pragyan Jha, Samit K. Ray. Suppression of Light-Induced Phase Segregations in Mixed Halide Perovskites through Ligand Passivation. The Journal of Physical Chemistry Letters 2025, 16 (7) , 1760-1768. https://doi.org/10.1021/acs.jpclett.4c03509
  2. Nuerbiya Aihemaiti, Siying Peng. Rationalizing Light-Induced Phase Segregation Reversal by Halide Oxidation and Diffusion in Mixed Halide Perovskites. ACS Energy Letters 2025, 10 (2) , 907-914. https://doi.org/10.1021/acsenergylett.4c03073
  3. Changbo Li, Changshun Chen, Weiyin Gao, He Dong, Yipeng Zhou, Zhongbin Wu, Chenxin Ran. Wide-Bandgap Lead Halide Perovskites for Next-Generation Optoelectronics: Current Status and Future Prospects. ACS Nano 2024, 18 (52) , 35130-35163. https://doi.org/10.1021/acsnano.4c12107
  4. Yusuke Daikoku, Takumi Yamada, Ai Shimazaki, Tomoya Nakamura, Atsushi Wakamiya, Yoshihiko Kanemitsu. Revealing the Dynamic Aspects of Photoinduced Halide Segregation in Mixed-Halide Cs0.15FA0.85PbI2Br Perovskite Films Using a Hyperspectral Imaging Technique. The Journal of Physical Chemistry Letters 2024, 15 (50) , 12341-12347. https://doi.org/10.1021/acs.jpclett.4c03077
  5. Md Habibur Rahman, Maitreyo Biswas, Arun Mannodi-Kanakkithodi. Understanding Defect-Mediated Ion Migration in Semiconductors using Atomistic Simulations and Machine Learning. ACS Materials Au 2024, 4 (6) , 557-573. https://doi.org/10.1021/acsmaterialsau.4c00095
  6. Halyna Okrepka, Yang Ding, Sushrut Ghonge, Anthony Ruth, Masaru Kuno. Excitation Intensity-Dependent Terminal Halide Photosegregation Stoichiometries in Formamidinium/Cesium Lead Iodide/Bromide [FACsPb(I1–xBrx)3] Thin Films. The Journal of Physical Chemistry Letters 2024, 15 (42) , 10488-10494. https://doi.org/10.1021/acs.jpclett.4c02008
  7. Tong Zhu, Luke Grater, Sam Teale, Eugenia S. Vasileiadou, Jonathan Sharir-Smith, Bin Chen, Mercouri G. Kanatzidis, Edward H. Sargent. Coupling Photogeneration with Thermodynamic Modeling of Light-Induced Alloy Segregation Enables the Identification of Stabilizing Dopants. Chemistry of Materials 2024, 36 (15) , 7438-7450. https://doi.org/10.1021/acs.chemmater.4c01402
  8. Xue Ren, Zhe-Yong Chen, Hui-Ling Hu, Yi Liu, Feng-Lei Jiang. Direct Observation of the Inhibition of Phase Segregation by Quaternary Ammonium in Mixed-Halide Perovskite. ACS Applied Energy Materials 2024, 7 (8) , 3245-3252. https://doi.org/10.1021/acsaem.4c00010
  9. Mantas Simenas, Anna Gagor, Juras Banys, Miroslaw Maczka. Phase Transitions and Dynamics in Mixed Three- and Low-Dimensional Lead Halide Perovskites. Chemical Reviews 2024, 124 (5) , 2281-2326. https://doi.org/10.1021/acs.chemrev.3c00532
  10. Lena Merten, Timo Eberle, Ekaterina Kneschaurek, Niels Scheffczyk, Paul Zimmermann, Ivan Zaluzhnyy, Azat Khadiev, Florian Bertram, Fabian Paulus, Alexander Hinderhofer, Frank Schreiber. Halide Segregated Crystallization of Mixed-Halide Perovskites Revealed by In Situ GIWAXS. ACS Applied Materials & Interfaces 2024, 16 (7) , 8913-8921. https://doi.org/10.1021/acsami.3c18623
  11. Gourab Sarkar, Priyanka Deswal, Dibyajyoti Ghosh. Ion Diffusion Dynamics and Halogen Mixing at the Heterojunction of Halide Perovskites: Atomistic Insights. The Journal of Physical Chemistry C 2024, 128 (4) , 1762-1772. https://doi.org/10.1021/acs.jpcc.3c06329
  12. Deepani V. Athapaththu, Martin E. Kordesch, Jixin Chen. Monitoring Phase Separation and Dark Recovery in Mixed Halide Perovskite Clusters and Single Crystals Using In Situ Spectromicroscopy. The Journal of Physical Chemistry Letters 2024, 15 (4) , 1105-1111. https://doi.org/10.1021/acs.jpclett.3c03280
  13. Subham Paramanik, Soirik Dan, Amlan J. Pal. Formation of Dual Bands in Mixed-Halide Perovskites During Photoinduced Halide Segregation. ACS Energy Letters 2024, 9 (1) , 56-63. https://doi.org/10.1021/acsenergylett.3c02082
  14. Grigorii Verkhogliadov, Ross Haroldson, Dmitry Gets, Anvar A. Zakhidov, Sergey V. Makarov. Temperature Dependence of Photoinduced Phase Segregation in Bromide-Rich Mixed Halide Perovskites. The Journal of Physical Chemistry C 2023, 127 (50) , 24339-24349. https://doi.org/10.1021/acs.jpcc.3c04887
  15. Mutibah Alanazi, Ashley Marshall, Shaoni Kar, Yincheng Liu, Jinwoo Kim, Henry J. Snaith, Robert A. Taylor, Tristan Farrow. Stability of Mixed Lead Halide Perovskite Films Encapsulated in Cyclic Olefin Copolymer at Room and Cryogenic Temperatures. The Journal of Physical Chemistry Letters 2023, 14 (50) , 11333-11341. https://doi.org/10.1021/acs.jpclett.3c02733
  16. Sang Woo Park, Jin Hyuck Heo, Hyong Joon Lee, Hyungjun Kim, Sang Hyuk Im, Ki-Ha Hong. Compositional Design for High-Efficiency All-Inorganic Tin Halide Perovskite Solar Cells. ACS Energy Letters 2023, 8 (12) , 5061-5069. https://doi.org/10.1021/acsenergylett.3c02032
  17. Paramesh Chandra, Swapan Kumar Mandal. Observation of Negative Photoconductivity in (CH3NH3)3Bi2(BrxCl1–x)9: Correlating Ion Migration, Stability, and Efficiency in Mixed Halide Perovskite Solar Cell. The Journal of Physical Chemistry C 2023, 127 (47) , 23109-23121. https://doi.org/10.1021/acs.jpcc.3c06427
  18. Yuhuan Li, Tongxiao Yang, Yaqi She, Beizheng Xu, Yonghui Du, Miao Zhang. Halide Double Perovskites Cs2PdBr6–xIx with Tunable Bandgaps for Solar Cells. Inorganic Chemistry 2023, 62 (47) , 19248-19255. https://doi.org/10.1021/acs.inorgchem.3c02516
  19. Marianna D’Amato, Lucien Belzane, Corentin Dabard, Mathieu Silly, Gilles Patriarche, Quentin Glorieux, Hanna Le Jeannic, Emmanuel Lhuillier, Alberto Bramati. Highly Photostable Zn-Treated Halide Perovskite Nanocrystals for Efficient Single Photon Generation. Nano Letters 2023, 23 (22) , 10228-10235. https://doi.org/10.1021/acs.nanolett.3c02739
  20. Hannah Funk, Tal Binyamin, Lioz Etgar, Oleksandra Shargaieva, Thomas Unold, Alberto Eljarrat, Christoph T. Koch, Daniel Abou-Ras. Phase Segregation Mechanisms in Mixed-Halide CsPb(BrxI1–x)3 Nanocrystals in Dependence of Their Sizes and Their Initial [Br]:[I] Ratios. ACS Materials Au 2023, 3 (6) , 687-698. https://doi.org/10.1021/acsmaterialsau.3c00056
  21. Anthony Ruth, Masaru Kuno. Modeling the Photoelectrochemical Evolution of Lead-Based, Mixed-Halide Perovskites Due to Photosegregation. ACS Nano 2023, 17 (20) , 20502-20511. https://doi.org/10.1021/acsnano.3c07165
  22. Jie Xu, Suresh Kumar Podapangi, Sathy Harshavardhan Reddy, Luigi Angelo Castriotta, Aldo Di Carlo, Thomas M. Brown. Key Parameters and Thresholds Values for Obtaining High Performance Perovskite Solar Cells Indoors from Full Br Compositional and Bandgap Engineering. ACS Applied Energy Materials 2023, 6 (20) , 10215-10224. https://doi.org/10.1021/acsaem.2c03394
  23. Anthony Ruth, Halyna Okrepka, Prashant Kamat, Masaru Kuno. Thermodynamic Band Gap Model for Photoinduced Phase Segregation in Mixed-Halide Perovskites. The Journal of Physical Chemistry C 2023, 127 (37) , 18547-18559. https://doi.org/10.1021/acs.jpcc.3c04708
  24. Yu-Hsien Chiang, Kyle Frohna, Hayden Salway, Anna Abfalterer, Linfeng Pan, Bart Roose, Miguel Anaya, Samuel D. Stranks. Vacuum-Deposited Wide-Bandgap Perovskite for All-Perovskite Tandem Solar Cells. ACS Energy Letters 2023, 8 (6) , 2728-2737. https://doi.org/10.1021/acsenergylett.3c00564
  25. Zhaojian Xu, Daniel D. Astridge, Ross A. Kerner, Xinjue Zhong, Junnan Hu, Jisu Hong, Jesse A. Wisch, Kai Zhu, Joseph J. Berry, Antoine Kahn, Alan Sellinger, Barry P. Rand. Origins of Photoluminescence Instabilities at Halide Perovskite/Organic Hole Transport Layer Interfaces. Journal of the American Chemical Society 2023, 145 (21) , 11846-11858. https://doi.org/10.1021/jacs.3c03539
  26. Fabian Hartl, Veronika Brune, Sophie Lüggert, Corinna Hegemann, David van Gerven, Michael Wilhelm, Seulgi Ji, Heechae Choi, Sanjay Mathur. Direct Synthesis of Two-Dimensional SnSe and SnSe2 through Molecular Scale Preorganization. Inorganic Chemistry 2023, 62 (16) , 6274-6287. https://doi.org/10.1021/acs.inorgchem.2c04083
  27. Kunal Datta, Alessandro Caiazzo, Michael A. Hope, Junyu Li, Aditya Mishra, Manuel Cordova, Zehua Chen, Lyndon Emsley, Martijn M. Wienk, René A. J. Janssen. Light-Induced Halide Segregation in 2D and Quasi-2D Mixed-Halide Perovskites. ACS Energy Letters 2023, 8 (4) , 1662-1670. https://doi.org/10.1021/acsenergylett.3c00160
  28. Parth Raval, Mohammad Ali Akhavan Kazemi, Julie Ruellou, Julien Trébosc, Olivier Lafon, Laurent Delevoye, Frédéric Sauvage, G. N. Manjunatha Reddy. Examining a Year-Long Chemical Degradation Process and Reaction Kinetics in Pristine and Defect-Passivated Lead Halide Perovskites. Chemistry of Materials 2023, 35 (7) , 2904-2917. https://doi.org/10.1021/acs.chemmater.2c03803
  29. Zehua Chen, Haibo Xue, Geert Brocks, Peter A. Bobbert, Shuxia Tao. Thermodynamic Origin of the Photostability of the Two-Dimensional Perovskite PEA2Pb(I1–xBrx)4. ACS Energy Letters 2023, 8 (2) , 943-949. https://doi.org/10.1021/acsenergylett.2c02463
  30. Yun Liu, Jean-Philippe Banon, Kyle Frohna, Yu-Hsien Chiang, Ganbaatar Tumen-Ulzii, Samuel D. Stranks, Marcel Filoche, Richard H. Friend. The Electronic Disorder Landscape of Mixed Halide Perovskites. ACS Energy Letters 2023, 8 (1) , 250-258. https://doi.org/10.1021/acsenergylett.2c02352
  31. Irina Gushchina, Vadim Trepalin, Evgenii Zaitsev, Anthony Ruth, Masaru Kuno. Excitation Intensity- and Size-Dependent Halide Photosegregation in CsPb(I0.5Br0.5)3 Perovskite Nanocrystals. ACS Nano 2022, 16 (12) , 21636-21644. https://doi.org/10.1021/acsnano.2c10781
  32. Stefano Toso, Irina Gushchina, Allen G. Oliver, Liberato Manna, Masaru Kuno. Are Mixed-Halide Ruddlesden–Popper Perovskites Really Mixed?. ACS Energy Letters 2022, 7 (12) , 4242-4247. https://doi.org/10.1021/acsenergylett.2c01967
  33. Tik Lun Leung, Zhilin Ren, Ali Asgher Syed, Luca Grisanti, Aleksandra B. Djurišić, Jasminka Popović. Photoinduced Segregation Behavior in 2D Mixed Halide Perovskite: Effects of Light and Heat. ACS Energy Letters 2022, 7 (10) , 3500-3508. https://doi.org/10.1021/acsenergylett.2c01688
  34. So-Yeon Ju, Wan In Lee, Hui-Seon Kim. Enhanced Phase Stability of Compressive Strain-Induced Perovskite Crystals. ACS Applied Materials & Interfaces 2022, 14 (35) , 39996-40004. https://doi.org/10.1021/acsami.2c10450
  35. Ruilin Zheng, Jumpei Ueda, Kenji Shinozaki, Setsuhisa Tanabe. Reversible Phase Segregation and Amorphization of Mixed-Halide Perovskite Nanocrystals in Glass Matrices. The Journal of Physical Chemistry Letters 2022, 13 (33) , 7809-7815. https://doi.org/10.1021/acs.jpclett.2c02261
  36. T. H. Chan, N. T. Taylor, S. Sundaram, S. P. Hepplestone. Phase Stability and Electronic Properties of Hybrid Organic–Inorganic Perovskite Solid Solution (CH(NH2)2)x(CH3NH3)1–xPb(BryI1–y)3 as a Function of Composition. The Journal of Physical Chemistry C 2022, 126 (32) , 13640-13648. https://doi.org/10.1021/acs.jpcc.2c03555
  37. Po-Kai Kung, Kuang-I Lin, Chun-Sheng Wu, Ming-Hsien Li, Chia-Ru Chan, Raja Rajendran, Chen-Fu Lin, Peter Chen. Visualization of Ion Migration in an Inorganic Mixed Halide Perovskite by One-Photon and Multiphoton Absorption: Effect of Guanidinium A-Site Cation Incorporation. The Journal of Physical Chemistry Letters 2022, 13 (30) , 6944-6955. https://doi.org/10.1021/acs.jpclett.2c01515
  38. Taehee Kim, Seongsik Jeong, Kyeong-Hwan Kim, Hyunseok Shim, Dongho Kim, Hae-Jin Kim. Engineered Surface Halide Defects by Two-Dimensional Perovskite Passivation for Deformable Intelligent Photodetectors. ACS Applied Materials & Interfaces 2022, 14 (22) , 26004-26013. https://doi.org/10.1021/acsami.2c03089
  39. Niara E. Wright, Xixi Qin, Junwei Xu, Leah L. Kelly, Steven P. Harvey, Michael F. Toney, Volker Blum, Adrienne D. Stiff-Roberts. Influence of Annealing and Composition on the Crystal Structure of Mixed-Halide, Ruddlesden–Popper Perovskites. Chemistry of Materials 2022, 34 (7) , 3109-3122. https://doi.org/10.1021/acs.chemmater.1c04213
  40. S. Akash, Altaf Pasha, R. Geetha Balakrishna. Dissipation of Charge Accumulation and Suppression of Phase Segregation in Mixed Halide Perovskite Solar Cells via Nanoribbons. ACS Applied Energy Materials 2022, 5 (3) , 2727-2737. https://doi.org/10.1021/acsaem.1c03229
  41. Yuhang Sheng, Weijian Chen, Fengrui Hu, Cihui Liu, Yunsong Di, Chong Sheng, Zhihui Chen, Baohua Jia, Xiaoming Wen, Zhixing Gan. Mechanism of Photoinduced Phase Segregation in Mixed-Halide Perovskite Microplatelets and Its Application in Micropatterning. ACS Applied Materials & Interfaces 2022, 14 (10) , 12412-12422. https://doi.org/10.1021/acsami.2c00590
  42. Dawid Drozdowski, Anna Gągor, Dagmara Stefańska, Jan K. Zarȩba, Katarzyna Fedoruk, Mirosław Mączka, Adam Sieradzki. Three-Dimensional Methylhydrazinium Lead Halide Perovskites: Structural Changes and Effects on Dielectric, Linear, and Nonlinear Optical Properties Entailed by the Halide Tuning. The Journal of Physical Chemistry C 2022, 126 (3) , 1600-1610. https://doi.org/10.1021/acs.jpcc.1c07911
  43. Shangchao Lin, Lifu Yan, Lingling Zhao, Zhuangli Cai, Zuolin Liu, Bin Yang, Min Yang, Changying Zhao. Strain Engineering for Tailored Carrier Transport and Thermoelectric Performance in Mixed Halide Perovskites CsPb(I1–xBrx)3. ACS Applied Energy Materials 2021, 4 (12) , 14508-14519. https://doi.org/10.1021/acsaem.1c03177
  44. Kaiyu Wang, Qing Yao, Jie Zhang, Chenyu Shang, Changqian Li, Feitong Chen, Tianliang Zhou, Haiqing Sun, Weiwei Zhang, Huiling Zhu, Jianxu Ding. Short-Range Migration of A-Site Cations Inhibit Photoinduced Phase Segregation in FAxMAyCs1–x–yPbI3–zBrz Single Crystals. The Journal of Physical Chemistry C 2021, 125 (42) , 23050-23057. https://doi.org/10.1021/acs.jpcc.1c08346
  45. Yuan Liu, Yitong Dong, Tong Zhu, Dongxin Ma, Andrew Proppe, Bin Chen, Chao Zheng, Yi Hou, Seungjin Lee, Bin Sun, Eui Hyuk Jung, Fanglong Yuan, Ya-kun Wang, Laxmi Kishore Sagar, Sjoerd Hoogland, F. Pelayo García de Arquer, Min-Jae Choi, Kamalpreet Singh, Shana O. Kelley, Oleksandr Voznyy, Zheng-Hong Lu, Edward H. Sargent. Bright and Stable Light-Emitting Diodes Based on Perovskite Quantum Dots in Perovskite Matrix. Journal of the American Chemical Society 2021, 143 (38) , 15606-15615. https://doi.org/10.1021/jacs.1c02148
  46. Hyejin Choe, Dohyun Jeon, Seon Joo Lee, Junsang Cho. Mixed or Segregated: Toward Efficient and Stable Mixed Halide Perovskite-Based Devices. ACS Omega 2021, 6 (38) , 24304-24315. https://doi.org/10.1021/acsomega.1c03714
  47. Seongrok Seo, Sooeun Shin, Eunsoo Kim, Seonghwa Jeong, Nam-Gyu Park, Hyunjung Shin. Amorphous TiO2 Coatings Stabilize Perovskite Solar Cells. ACS Energy Letters 2021, 6 (9) , 3332-3341. https://doi.org/10.1021/acsenergylett.1c01446
  48. Tim W. J. van de Goor, Yun Liu, Sascha Feldmann, Sean A. Bourelle, Timo Neumann, Thomas Winkler, Nicola D. Kelly, Cheng Liu, Michael A. Jones, Steffen P. Emge, Richard H. Friend, Bartomeu Monserrat, Felix Deschler, Siân E. Dutton. Impact of Orientational Glass Formation and Local Strain on Photo-Induced Halide Segregation in Hybrid Metal-Halide Perovskites. The Journal of Physical Chemistry C 2021, 125 (27) , 15025-15034. https://doi.org/10.1021/acs.jpcc.1c03169
  49. Yuxiao Guo, Xingtian Yin, Dan Liu, Jie Liu, Cong Zhang, Haixia Xie, Yawei Yang, Wenxiu Que. Photoinduced Self-healing of Halide Segregation in Mixed-halide Perovskites. ACS Energy Letters 2021, 6 (7) , 2502-2511. https://doi.org/10.1021/acsenergylett.1c01040
  50. Ilia M. Pavlovetc, Anthony Ruth, Irina Gushchina, Loc Ngo, Shubin Zhang, Zhuoming Zhang, Masaru Kuno. Distinguishing Models for Mixed Halide Lead Perovskite Photosegregation via Terminal Halide Stoichiometry. ACS Energy Letters 2021, 6 (6) , 2064-2071. https://doi.org/10.1021/acsenergylett.1c00790
  51. Gailan Al-Dainy, Fumiya Watanabe, Alexandru S. Biris, Shawn E. Bourdo. Surface Passivation of Triple-Cation Perovskite via Organic Halide-Saturated Antisolvent for Inverted Planar Solar Cells. ACS Applied Energy Materials 2021, 4 (4) , 3297-3309. https://doi.org/10.1021/acsaem.0c03059
  52. Jeffrey T. DuBose, Preethi S. Mathew, Junsang Cho, Masaru Kuno, Prashant V. Kamat. Modulation of Photoinduced Iodine Expulsion in Mixed Halide Perovskites with Electrochemical Bias. The Journal of Physical Chemistry Letters 2021, 12 (10) , 2615-2621. https://doi.org/10.1021/acs.jpclett.1c00367
  53. Pietro Caprioglio, Sebastián Caicedo-Dávila, Terry Chien-Jen Yang, Christian M. Wolff, Francisco Peña-Camargo, Peter Fiala, Bernd Rech, Christophe Ballif, Daniel Abou-Ras, Martin Stolterfoht, Steve Albrecht, Quentin Jeangros, Dieter Neher. Nano-emitting Heterostructures Violate Optical Reciprocity and Enable Efficient Photoluminescence in Halide-Segregated Methylammonium-Free Wide Bandgap Perovskites. ACS Energy Letters 2021, 6 (2) , 419-428. https://doi.org/10.1021/acsenergylett.0c02270
  54. Alexander J. Knight, Juliane Borchert, Robert D. J. Oliver, Jay B. Patel, Paolo G. Radaelli, Henry J. Snaith, Michael B. Johnston, Laura M. Herz. Halide Segregation in Mixed-Halide Perovskites: Influence of A-Site Cations. ACS Energy Letters 2021, 6 (2) , 799-808. https://doi.org/10.1021/acsenergylett.0c02475
  55. Prashant V. Kamat, Masaru Kuno. Halide Ion Migration in Perovskite Nanocrystals and Nanostructures. Accounts of Chemical Research 2021, 54 (3) , 520-531. https://doi.org/10.1021/acs.accounts.0c00749
  56. Junke Jiang, Feng Liu, Ionut Tranca, Qing Shen, Shuxia Tao. Atomistic and Electronic Origin of Phase Instability of Metal Halide Perovskites. ACS Applied Energy Materials 2020, 3 (12) , 11548-11558. https://doi.org/10.1021/acsaem.0c00791
  57. Finn Babbe, Eloïse Masquelier, Zhi Zheng, Carolin M. Sutter-Fella. Flash Formation of I-Rich Clusters during Multistage Halide Segregation Studied in MAPbI1.5Br1.5. The Journal of Physical Chemistry C 2020, 124 (45) , 24608-24615. https://doi.org/10.1021/acs.jpcc.0c07063
  58. Mohammad Rahil, Pramod Rajput, Dibyajyoti Ghosh, Shahab Ahmad. Highly Tunable Single-Phase Excitons in Mixed Halide Layered Perovskites. ACS Applied Electronic Materials 2020, 2 (10) , 3199-3210. https://doi.org/10.1021/acsaelm.0c00554
  59. Miłosz Martynow, Damian Głowienka, Yulia Galagan, Julien Guthmuller. Effects of Bromine Doping on the Structural Properties and Band Gap of CH3NH3Pb(I1–xBrx)3 Perovskite. ACS Omega 2020, 5 (41) , 26946-26953. https://doi.org/10.1021/acsomega.0c04406
  60. Erjin Zheng, Zhiyin Niu, Gabriella A. Tosado, Hao Dong, Yaqoub Albrikan, Qiuming Yu. Revealing Stability of Inverted Planar MA-Free Perovskite Solar Cells and Electric Field-Induced Phase Instability. The Journal of Physical Chemistry C 2020, 124 (34) , 18805-18815. https://doi.org/10.1021/acs.jpcc.0c05357
  61. Yutao Wang, Xinwei Guan, Weijian Chen, Jack Yang, Long Hu, Jiong Yang, Sean Li, Kourosh Kalantar-Zadeh, Xiaoming Wen, Tom Wu. Illumination-Induced Phase Segregation and Suppressed Solubility Limit in Br-Rich Mixed-Halide Inorganic Perovskites. ACS Applied Materials & Interfaces 2020, 12 (34) , 38376-38385. https://doi.org/10.1021/acsami.0c10363
  62. Stefania Cacovich, Davina Messou, Adrien Bercegol, Solène Béchu, Armelle Yaiche, Hamza Shafique, Jean Rousset, Philip Schulz, Muriel Bouttemy, Laurent Lombez. Light-Induced Passivation in Triple Cation Mixed Halide Perovskites: Interplay between Transport Properties and Surface Chemistry. ACS Applied Materials & Interfaces 2020, 12 (31) , 34784-34794. https://doi.org/10.1021/acsami.0c06844
  63. Yang Huang, Tao Zhang, Jing Wang, Shao-Gang Xu, Peng Zhang, Shiyou Chen, Wan-Jian Yin, Xiuwen Zhang, Su-Huai Wei. Design of Multifunctional Quinternary Metal-Halide Perovskite Compounds Based on Cation–Anion Co-Ordering. Chemistry of Materials 2020, 32 (14) , 5949-5957. https://doi.org/10.1021/acs.chemmater.0c00674
  64. Carolin Rehermann, Aboma Merdasa, Klara Suchan, Vincent Schröder, Florian Mathies, Eva L. Unger. Origin of Ionic Inhomogeneity in MAPb(IxBr1–x)3 Perovskite Thin Films Revealed by In-Situ Spectroscopy during Spin Coating and Annealing. ACS Applied Materials & Interfaces 2020, 12 (27) , 30343-30352. https://doi.org/10.1021/acsami.0c05894
  65. Hannah Funk, Oleksandra Shargaieva, Alberto Eljarrat, Eva L. Unger, Christoph T. Koch, Daniel Abou-Ras. In Situ TEM Monitoring of Phase-Segregation in Inorganic Mixed Halide Perovskite. The Journal of Physical Chemistry Letters 2020, 11 (13) , 4945-4950. https://doi.org/10.1021/acs.jpclett.0c01296
  66. David O. Tiede, Mauricio E. Calvo, Juan F. Galisteo-López, Hernán Míguez. Local Rearrangement of the Iodide Defect Structure Determines the Phase Segregation Effect in Mixed-Halide Perovskites. The Journal of Physical Chemistry Letters 2020, 11 (12) , 4911-4916. https://doi.org/10.1021/acs.jpclett.0c01127
  67. Preethi Susan Mathew, Gergely F. Samu, Csaba Janáky, Prashant V. Kamat. Iodine (I) Expulsion at Photoirradiated Mixed Halide Perovskite Interface. Should I Stay or Should I Go?. ACS Energy Letters 2020, 5 (6) , 1872-1880. https://doi.org/10.1021/acsenergylett.0c00925
  68. Sungmin Kim, Taedaehyeong Eom, Ye-Seol Ha, Ki-Ha Hong, Hyungjun Kim. Thermodynamics of Multicomponent Perovskites: A Guide to Highly Efficient and Stable Solar Cell Materials. Chemistry of Materials 2020, 32 (10) , 4265-4272. https://doi.org/10.1021/acs.chemmater.0c00893
  69. Jongseob Kim, Sung-Hoon Lee, Sang Hyuk Im, Ki-Ha Hong. Phase Selection of Cesium Lead Triiodides through Surface Ligand Engineering. The Journal of Physical Chemistry Letters 2020, 11 (10) , 4232-4238. https://doi.org/10.1021/acs.jpclett.0c00499
  70. Nikita Rybin, Dibyajyoti Ghosh, Jeremy Tisdale, Shreetu Shrestha, Michael Yoho, Duc Vo, Jacky Even, Claudine Katan, Wanyi Nie, Amanda J. Neukirch, Sergei Tretiak. Effects of Chlorine Mixing on Optoelectronics, Ion Migration, and Gamma-Ray Detection in Bromide Perovskites. Chemistry of Materials 2020, 32 (5) , 1854-1863. https://doi.org/10.1021/acs.chemmater.9b04244
  71. Juvinch R. Vicente, Jixin Chen. Phase Segregation and Photothermal Remixing of Mixed-Halide Lead Perovskites. The Journal of Physical Chemistry Letters 2020, 11 (5) , 1802-1807. https://doi.org/10.1021/acs.jpclett.9b03734
  72. Alex Aziz, Nicholas Aristidou, Xiangnan Bu, Robert J. E. Westbrook, Saif A. Haque, M. Saiful Islam. Understanding the Enhanced Stability of Bromide Substitution in Lead Iodide Perovskites. Chemistry of Materials 2020, 32 (1) , 400-409. https://doi.org/10.1021/acs.chemmater.9b04000
  73. Tor Elmelund, Brian Seger, Masaru Kuno, Prashant V. Kamat. How Interplay between Photo and Thermal Activation Dictates Halide Ion Segregation in Mixed Halide Perovskites. ACS Energy Letters 2020, 5 (1) , 56-63. https://doi.org/10.1021/acsenergylett.9b02265
  74. Alessandro Senocrate, Gee Yeong Kim, Michael Grätzel, Joachim Maier. Thermochemical Stability of Hybrid Halide Perovskites. ACS Energy Letters 2019, 4 (12) , 2859-2870. https://doi.org/10.1021/acsenergylett.9b01605
  75. Ekaterina I. Marchenko, Sergey A. Fateev, Andrey A. Petrov, Eugene A. Goodilin, Nikolay N. Eremin, Alexey B. Tarasov. Transferable Approach of Semi-Empirical Modeling of Disordered Mixed-Halide Hybrid Perovskites CH3NH3Pb(I1–xBrx)3: Prediction of Thermodynamic Properties, Phase Stability, and Deviations from Vegard’s Law. The Journal of Physical Chemistry C 2019, 123 (42) , 26036-26040. https://doi.org/10.1021/acs.jpcc.9b08995
  76. Weisheng Fan, Yongliang Shi, Tongfei Shi, Shenglong Chu, Wenjing Chen, Kester O. Ighodalo, Jin Zhao, Xinhua Li, Zhengguo Xiao. Suppression and Reversion of Light-Induced Phase Separation in Mixed-Halide Perovskites by Oxygen Passivation. ACS Energy Letters 2019, 4 (9) , 2052-2058. https://doi.org/10.1021/acsenergylett.9b01383
  77. Hua Wu, Huimin Zhu, Axel Erbing, Malin B. Johansson, Soham Mukherjee, Gabriel J. Man, Håkan Rensmo, Michael Odelius, Erik M. J. Johansson. Bandgap Tuning of Silver Bismuth Iodide via Controllable Bromide Substitution for Improved Photovoltaic Performance. ACS Applied Energy Materials 2019, 2 (8) , 5356-5362. https://doi.org/10.1021/acsaem.9b00914
  78. Tor Elmelund, Rebecca A. Scheidt, Brian Seger, Prashant V. Kamat. Bidirectional Halide Ion Exchange in Paired Lead Halide Perovskite Films with Thermal Activation. ACS Energy Letters 2019, 4 (8) , 1961-1969. https://doi.org/10.1021/acsenergylett.9b01280
  79. Diego Guedes-Sobrinho, Ivan Guilhon, Marcelo Marques, Lara K. Teles. Relativistic DFT-1/2 Calculations Combined with a Statistical Approach for Electronic and Optical Properties of Mixed Metal Hybrid Perovskites. The Journal of Physical Chemistry Letters 2019, 10 (15) , 4245-4251. https://doi.org/10.1021/acs.jpclett.9b01499
  80. Rhiannon M. Kennard, Clayton J. Dahlman, Hidenori Nakayama, Ryan A. DeCrescent, Jon A. Schuller, Ram Seshadri, Kunal Mukherjee, Michael L. Chabinyc. Phase Stability and Diffusion in Lateral Heterostructures of Methyl Ammonium Lead Halide Perovskites. ACS Applied Materials & Interfaces 2019, 11 (28) , 25313-25321. https://doi.org/10.1021/acsami.9b06069
  81. Gustavo M. Dalpian, Xin-Gang Zhao, Lawrence Kazmerski, Alex Zunger. Formation and Composition-Dependent Properties of Alloys of Cubic Halide Perovskites. Chemistry of Materials 2019, 31 (7) , 2497-2506. https://doi.org/10.1021/acs.chemmater.8b05329
  82. Wenjun Shi, Yong Wang, Taiyang Zhang, Haijuan Zhang, Yixin Zhao, Jie Chen. Fast Charge Diffusion in MAPb(I1–xBrx)3 Films for High-Efficiency Solar Cells Revealed by Ultrafast Time-Resolved Reflectivity. The Journal of Physical Chemistry A 2019, 123 (13) , 2674-2678. https://doi.org/10.1021/acs.jpca.9b00978
  83. Caleb C. Boyd, Rongrong Cheacharoen, Tomas Leijtens, Michael D. McGehee. Understanding Degradation Mechanisms and Improving Stability of Perovskite Photovoltaics. Chemical Reviews 2019, 119 (5) , 3418-3451. https://doi.org/10.1021/acs.chemrev.8b00336
  84. Liang Chen, Yan-Yan Tan, Zhi-Xin Chen, Tan Wang, Shu Hu, Zi-Ang Nan, Li-Qiang Xie, Yong Hui, Jing-Xin Huang, Chao Zhan, Su-Heng Wang, Jian-Zhang Zhou, Jia-Wei Yan, Bing-Wei Mao, Zhong-Qun Tian. Toward Long-Term Stability: Single-Crystal Alloys of Cesium-Containing Mixed Cation and Mixed Halide Perovskite. Journal of the American Chemical Society 2019, 141 (4) , 1665-1671. https://doi.org/10.1021/jacs.8b11610
  85. Alexander J. Knight, Adam D. Wright, Jay B. Patel, David P. McMeekin, Henry J. Snaith, Michael B. Johnston, Laura M. Herz. Electronic Traps and Phase Segregation in Lead Mixed-Halide Perovskite. ACS Energy Letters 2019, 4 (1) , 75-84. https://doi.org/10.1021/acsenergylett.8b02002
  86. Amanda J. Neukirch, Iwnetim I. Abate, Liujiang Zhou, Wanyi Nie, Hsinhan Tsai, Laurent Pedesseau, Jacky Even, Jared J. Crochet, Aditya D. Mohite, Claudine Katan, Sergei Tretiak. Geometry Distortion and Small Polaron Binding Energy Changes with Ionic Substitution in Halide Perovskites. The Journal of Physical Chemistry Letters 2018, 9 (24) , 7130-7136. https://doi.org/10.1021/acs.jpclett.8b03343
  87. Fabian Ruf, Pascal Rietz, Meltem F. Aygüler, Ina Kelz, Pablo Docampo, Heinz Kalt, Michael Hetterich. The Bandgap as a Moving Target: Reversible Bandgap Instabilities in Multiple-Cation Mixed-Halide Perovskite Solar Cells. ACS Energy Letters 2018, 3 (12) , 2995-3001. https://doi.org/10.1021/acsenergylett.8b01857
  88. Rebecca A. Belisle, Kevin A. Bush, Luca Bertoluzzi, Aryeh Gold-Parker, Michael F. Toney, Michael D. McGehee. Impact of Surfaces on Photoinduced Halide Segregation in Mixed-Halide Perovskites. ACS Energy Letters 2018, 3 (11) , 2694-2700. https://doi.org/10.1021/acsenergylett.8b01562
  89. Anthony Ruth, Michael C. Brennan, Sergiu Draguta, Yurii V. Morozov, Maksym Zhukovskyi, Boldizsar Janko, Peter Zapol, Masaru Kuno. Vacancy-Mediated Anion Photosegregation Kinetics in Mixed Halide Hybrid Perovskites: Coupled Kinetic Monte Carlo and Optical Measurements. ACS Energy Letters 2018, 3 (10) , 2321-2328. https://doi.org/10.1021/acsenergylett.8b01369
  90. Meiying Leng, Ying Yang, Zhengwu Chen, Wanru Gao, Jian Zhang, Guangda Niu, Dengbing Li, Haisheng Song, Jianbing Zhang, Song Jin, Jiang Tang. Surface Passivation of Bismuth-Based Perovskite Variant Quantum Dots To Achieve Efficient Blue Emission. Nano Letters 2018, 18 (9) , 6076-6083. https://doi.org/10.1021/acs.nanolett.8b03090
  91. Pronoy Nandi, Chandan Giri, Diptikanta Swain, U. Manju, Subhendra D. Mahanti, Dinesh Topwal. Temperature Dependent Photoinduced Reversible Phase Separation in Mixed-Halide Perovskite. ACS Applied Energy Materials 2018, 1 (8) , 3807-3814. https://doi.org/10.1021/acsaem.8b00587
  92. Aron Walsh, Samuel D. Stranks. Taking Control of Ion Transport in Halide Perovskite Solar Cells. ACS Energy Letters 2018, 3 (8) , 1983-1990. https://doi.org/10.1021/acsenergylett.8b00764
  93. Junke Jiang, Chidozie K. Onwudinanti, Ross A. Hatton, Peter A. Bobbert, Shuxia Tao. Stabilizing Lead-Free All-Inorganic Tin Halide Perovskites by Ion Exchange. The Journal of Physical Chemistry C 2018, 122 (31) , 17660-17667. https://doi.org/10.1021/acs.jpcc.8b04013
  94. Dhruba B. Khadka, Yasuhiro Shirai, Masatoshi Yanagida, Takeshi Noda, Kenjiro Miyano. Tailoring the Open-Circuit Voltage Deficit of Wide-Band-Gap Perovskite Solar Cells Using Alkyl Chain-Substituted Fullerene Derivatives. ACS Applied Materials & Interfaces 2018, 10 (26) , 22074-22082. https://doi.org/10.1021/acsami.8b04439
  95. Weixin Huang, Seog Joon Yoon, Pitambar Sapkota. Effect of Light Illumination on Mixed Halide Lead Perovskites: Reversible or Irreversible Transformation. ACS Applied Energy Materials 2018, 1 (6) , 2859-2865. https://doi.org/10.1021/acsaem.8b00513
  96. Alex M. Ganose, Saya Matsumoto, John Buckeridge, David O. Scanlon. Defect Engineering of Earth-Abundant Solar Absorbers BiSI and BiSeI. Chemistry of Materials 2018, 30 (11) , 3827-3835. https://doi.org/10.1021/acs.chemmater.8b01135
  97. Abhoy Karmakar, Abdelrahman M. Askar, Guy M. Bernard, Victor V. Terskikh, Michelle Ha, Sahil Patel, Karthik Shankar, Vladimir K. Michaelis. Mechanochemical Synthesis of Methylammonium Lead Mixed–Halide Perovskites: Unraveling the Solid-Solution Behavior Using Solid-State NMR. Chemistry of Materials 2018, 30 (7) , 2309-2321. https://doi.org/10.1021/acs.chemmater.7b05209
  98. Xiaofeng Tang, Marius van den Berg, Ening Gu, Anke Horneber, Gebhard J. Matt, Andres Osvet, Alfred J. Meixner, Dai Zhang, Christoph J. Brabec. Local Observation of Phase Segregation in Mixed-Halide Perovskite. Nano Letters 2018, 18 (3) , 2172-2178. https://doi.org/10.1021/acs.nanolett.8b00505
  99. Dianxing Ju, Yangyang Dang, Zonglong Zhu, Hongbin Liu, Chu-Chen Chueh, Xiaosong Li, Lei Wang, Xiaobo Hu, Alex K.-Y. Jen, Xutang Tao. Tunable Band Gap and Long Carrier Recombination Lifetime of Stable Mixed CH3NH3PbxSn1–xBr3 Single Crystals. Chemistry of Materials 2018, 30 (5) , 1556-1565. https://doi.org/10.1021/acs.chemmater.7b04565
  100. Michael C. Brennan, Sergiu Draguta, Prashant V. Kamat, Masaru Kuno. Light-Induced Anion Phase Segregation in Mixed Halide Perovskites. ACS Energy Letters 2018, 3 (1) , 204-213. https://doi.org/10.1021/acsenergylett.7b01151
Load more citations
Download PDF
Go to The Journal of Physical Chemistry Letters
Get e-Alerts
Get e-Alerts

The Journal of Physical Chemistry Letters

Cite this: J. Phys. Chem. Lett. 2016, 7, 6, 1083–1087
Click to copy citationCitation copied!
https://doi.org/10.1021/acs.jpclett.6b00226
Published March 7, 2016

Copyright © 2016 American Chemical Society. This publication is licensed under CC-BY.

Article Views

10k

Altmetric

-

Citations

341
Learn about these metrics

Article Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.

Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.

The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated.

  • Abstract

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 1

    Figure 1. Energy of mixing (top) and entropy of mixing (bottom) as functions of the CH3NH3Pb(I1–xBrx)3 alloy composition. The symbols are the values calculated for each configuration (eq 1). The solid lines show the behavior for the alloy at 200 K (blue), 300 K (green) and for a completely random alloy in the high T limit (red) within the generalized quasi-chemical approximation. The dashed line represents the convex hull.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 2

    Figure 2. Stable ordered structures identified for MAPbIBr2 and MAPbI1/2Br5/2, which minimize internal strain arising from the size mismatch between I and Br. The atoms at the corners of the octahedra are the halides Br (orange) and I (pink). The most stable structures are layered with iodine at the apical positions.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 3

    Figure 3. Calculated Helmholtz free energy as a function of the alloy composition and temperature as calculated within the generalized quasi-chemical approximation.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 4

    Figure 4. Predicted phase diagram of the MAPb(I1–xBrx)3 alloy. The purple and pink lines are the binodal and spinodal lines, respectively. The dashed horizontal line shows the miscibility gap at room temperature. A thermodynamically stable solid-solution can be formed in the white region only.

    High Resolution Image
    Download MS PowerPoint Slide

  • References

    This article references 40 other publications.

    1. 1
      Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S. I. Solvent Engineering for High-performance Inorganic-organic Hybrid Perovskite Solar Cells Nat. Mater. 2014, 13, 897 DOI: 10.1038/nmat4014
      1
      Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells
      Jeon, Nam Joong; Noh, Jun Hong; Kim, Young Chan; Yang, Woon Seok; Ryu, Seungchan; Seok, Sang Il
      Nature Materials (2014), 13 (9), 897-903CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      Organolead trihalide perovskite materials have been successfully used as light absorbers in efficient photovoltaic cells. Two different cell structures, based on mesoscopic metal oxides and planar heterojunctions have already demonstrated very impressive advances in performance. Here, we report a bilayer architecture comprising the key features of mesoscopic and planar structures obtained by a fully soln.-based process. We used CH3NH3 Pb(I1 - xBrx)3 (x = 0.1-0.15) as the absorbing layer and poly(triarylamine) as a hole-transporting material. The use of a mixed solvent of γ-butyrolactone and dimethylsulfoxide (DMSO) followed by toluene drop-casting leads to extremely uniform and dense perovskite layers via a CH3NH3I-PbI2-DMSO intermediate phase, and enables the fabrication of remarkably improved solar cells with a certified power-conversion efficiency of 16.2% and no hysteresis. These results provide important progress towards the understanding of the role of soln.-processing in the realization of low-cost and highly efficient perovskite solar cells.
    2. 2
      Zhou, H.; Chen, Q.; Li, G.; Luo, S.; Song, T.-b.; Duan, H.-S.; Hong, Z.; You, J.; Liu, Y.; Yang, Y. Interface Engineering of Highly Efficient Perovskite Solar Cells Science 2014, 345, 542 DOI: 10.1126/science.1254050
      2
      Interface engineering of highly efficient perovskite solar cells
      Zhou, Huanping; Chen, Qi; Li, Gang; Luo, Song; Song, Tze-bing; Duan, Hsin-Sheng; Hong, Ziruo; You, Jingbi; Liu, Yongsheng; Yang, Yang
      Science (Washington, DC, United States) (2014), 345 (6196), 542-546CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      Advancing perovskite solar cell technologies toward their theor. power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, the authors suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extn. at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on av., with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of the perovskite solar cells was conducted in air and from soln. at low temps., which should simplify manufg. of large-area perovskite devices that are inexpensive and perform at high levels.
    3. 3
      Ahn, N.; Son, D.-Y.; Jang, I.-H.; Kang, S. M.; Choi, M.; Park, N.-G. Highly Reproducible Perovskite Solar Cells with Average Efficiency of 18.3% and Best Efficiency of 19.7% Fabricated via Lewis Base Adduct of Lead(II) Iodide J. Am. Chem. Soc. 2015, 137, 8696 DOI: 10.1021/jacs.5b04930
      3
      Highly Reproducible Perovskite Solar Cells with Average Efficiency of 18.3% and Best Efficiency of 19.7% Fabricated via Lewis Base Adduct of Lead(II) Iodide
      Ahn, Namyoung; Son, Dae-Yong; Jang, In-Hyuk; Kang, Seong Min; Choi, Mansoo; Park, Nam-Gyu
      Journal of the American Chemical Society (2015), 137 (27), 8696-8699CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      High efficiency perovskite solar cells were fabricated reproducibly via Lewis base adduct of Pb(II) iodide. PbI2 was dissolved in N,N-dimethyformamide with equimolar N,N-DMSO and CH3NH3I. Stretching vibration of S=O appeared at 1045 cm-1 for bare DMSO, which was shifted to 1020 and 1015 cm-1 upon reacting DMSO with PbI2 and PbI2 + CH3NH3I, resp., indicative of forming the adduct of PbI2·DMSO and CH3NH3I·PbI2·DMSO due to interaction between Lewis base DMSO and/or iodide (I-) and Lewis acid PbI2. Spin-coating of a DMF soln. contg. PbI2, CH3NH3I, and DMSO (1:1:1 mol %) formed a transparent adduct film, which was converted to a dark brown film upon heating at low temp. of 65° for 1 min due to removal of the volatile DMSO from the adduct. The adduct-induced CH3NH3PbI3 exhibited high charge extn. characteristics with hole mobility ≤3.9 × 10-3 cm2/(V s) and slow recombination rate. Av. power conversion efficiency (PCE) of 18.3% was achieved from 41 cells and the best PCE of 19.7% was attained via adduct approach.
    4. 4
      Jeon, N. J.; Noh, J. H.; Yang, W. S.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. Compositional Engineering of Perovskite Materials for High-performance Solar Cells Nature 2015, 517, 476 DOI: 10.1038/nature14133
      4
      Compositional engineering of perovskite materials for high-performance solar cells
      Jeon, Nam Joong; Noh, Jun Hong; Yang, Woon Seok; Kim, Young Chan; Ryu, Seungchan; Seo, Jangwon; Seok, Sang Il
      Nature (London, United Kingdom) (2015), 517 (7535), 476-480CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      Here we combine the promising, owing to its comparatively narrow bandgap, but relatively unstable formamidinium lead iodide (FAPbI3) with methylammonium lead bromide (MAPbBr3) as the light-harvesting unit in a bilayer solar cell architecture. We investigated phase stability, morphol. of the perovskite layer, hysteresis in current-voltage characteristics, and overall performance as a function of chem. compn. Our results show that incorporation of MAPbBr3 into FAPbI3 stabilizes the perovskite phase of FAPbI3 and improves the power conversion efficiency of the solar cell to >18% under a std. illumination of 100 mW/cm2. These findings further emphasize the versatility and performance potential of inorg.-org. lead halide perovskite materials for photovoltaic applications.
    5. 5
      Hao, F.; Stoumpos, C. C.; Chang, R. P. H.; Kanatzidis, M. G. Anomalous Band Gap Behavior in Mixed Sn and Pb Perovskites Enables Broadening of Absorption Spectrum in Solar Cells J. Am. Chem. Soc. 2014, 136, 8094 DOI: 10.1021/ja5033259
      5
      Anomalous Band Gap Behavior in Mixed Sn and Pb Perovskites Enables Broadening of Absorption Spectrum in Solar Cells
      Hao, Feng; Stoumpos, Constantinos C.; Chang, Robert P. H.; Kanatzidis, Mercouri G.
      Journal of the American Chemical Society (2014), 136 (22), 8094-8099CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Perovskite-based solar cells have recently been catapulted to the cutting edge of thin-film photovoltaic research and development because of their promise for high-power conversion efficiencies and ease of fabrication. Two types of generic perovskites compds. have been used in cell fabrication: either Pb- or Sn-based. Here, we describe the performance of perovskite solar cells based on alloyed perovskite solid solns. of methylammonium tin iodide and its lead analog (CH3NH3Sn1-xPbxI3). We exploit the fact that, the energy band gaps of the mixed Pb/Sn compds. do not follow a linear trend (the Vegard's law) in between these two extremes of 1.55 and 1.35 eV, resp., but have narrower band-gap (<1.3 eV), thus extending the light absorption into the near-IR (∼1,050 nm). A series of soln.-processed solid-state photovoltaic devices using a mixt. of org. spiro-OMeTAD/lithium bis(trifluoromethylsulfonyl)imide/pyridinium additives as hole transport layer were fabricated and studied as a function of Sn to Pb ratio. Our results show that CH3NH3Sn0.5Pb0.5I3 has the broadest light absorption and highest short-circuit photocurrent d. ∼20 mA/cm2 (obtained under simulated full sunlight of 100 mW/cm2).
    6. 6
      Noh, J. H.; Im, S. H.; Heo, J. H.; Mandal, T. N.; Seok, S. I. Chemical Management for Colorful, Efficient, and Stable Inorganic-organic Hybrid Nanostructured Solar Cells Nano Lett. 2013, 13, 1764 DOI: 10.1021/nl400349b
      6
      Chemical Management for Colorful, Efficient, and Stable Inorganic-Organic Hybrid Nanostructured Solar Cells
      Noh, Jun Hong; Im, Sang Hyuk; Heo, Jin Hyuck; Mandal, Tarak N.; Seok, Sang Il
      Nano Letters (2013), 13 (4), 1764-1769CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Chem. tuned inorg.-org. hybrid materials, based on MeNH3(=MA)Pb(I1-xBrx)3 perovskites, have been studied using UV-visible absorption and x-ray diffraction patterns and applied to nanostructured solar cells. The band gap engineering brought about by the chem. management of MAPb(I1-xBrx)3 perovskites can be controllably tuned to cover almost the entire visible spectrum, enabling the realization of colorful solar cells. The authors demonstrate highly efficient solar cells exhibiting 12.3% in a power conversion efficiency of under std. AM 1.5, for the most efficient device, as a result of tunable compn. for the light harvester in conjunction with a mesoporous TiO2 film and a hole conducting polymer. Probably the works highlighted in this paper represent one step toward the realization of low-cost, high-efficiency, and long-term stability with colorful solar cells.
    7. 7
      Sadhanala, A.; Deschler, F.; Thomas, T. H.; Dutton, S. E.; Goedel, K. C.; Hanusch, F. C.; Lai, M. L.; Steiner, U.; Bein, T.; Docampo, P. Preparation of Single Phase Films of CH3NH3Pb(I1–xBrx)3 with Sharp Optical Band Edges J. Phys. Chem. Lett. 2014, 5, 2501 DOI: 10.1021/jz501332v
      7
      Preparation of Single-Phase Films of CH3NH3Pb(I1-xBrx)3 with Sharp Optical Band Edges
      Sadhanala, Aditya; Deschler, Felix; Thomas, Tudor H.; Dutton, Sian E.; Goedel, Karl C.; Hanusch, Fabian C.; Lai, May L.; Steiner, Ullrich; Bein, Thomas; Docampo, Pablo; Cahen, David; Friend, Richard H.
      Journal of Physical Chemistry Letters (2014), 5 (15), 2501-2505CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      Organometallic lead-halide perovskite-based solar cells now approach 18% efficiency. Introducing a mixt. of bromide and iodide in the halide compn. allows tuning of the optical bandgap. We prep. mixed bromide-iodide lead perovskite films CH3NH3Pb(I1-xBrx)3 (0 ≤ x ≤ 1) by spin-coating from soln. and obtain films with monotonically varying bandgaps across the full compn. range. Photothermal deflection spectroscopy, photoluminescence, and x-ray diffraction show that following suitable fabrication protocols these mixed lead-halide perovskite films form a single phase. The optical absorption edge of the pure tri-iodide and tribromide perovskites is sharp with Urbach energies of 15 and 23 meV, resp., and reaches a max. of 90 meV for CH3NH3PbI1.2Br1.8. We demonstrate a bromide-iodide lead perovskite film (CH3NH3PbI1.2Br1.8) with an optical bandgap of 1.94 eV, which is optimal for tandem cells of these materials with cryst. silicon devices.
    8. 8
      Kulkarni, S. A.; Baikie, T.; Boix, P. P.; Yantara, N.; Mathews, N.; Mhaisalkar, S. Band-gap Tuning of Lead Halide Perovskites Using a Sequential Deposition Process J. Mater. Chem. A 2014, 2, 9221 DOI: 10.1039/C4TA00435C
      8
      Band-gap tuning of lead halide perovskites using a sequential deposition process
      Kulkarni, Sneha A.; Baikie, Tom; Boix, Pablo P.; Yantara, Natalia; Mathews, Nripan; Mhaisalkar, Subodh
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2014), 2 (24), 9221-9225CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      Band-gap tuning of mixed anion lead halide perovskites (MAPb(I1-xBrx)2 (0 ≤ x ≤ 1)) has been demonstrated by means of a sequential deposition process. The optical properties of perovskite hybrids can be flexibly modified by changing (mixing) the concn. of halogen precursors. The concns. of precursor soln. as well as the conversion time play an important role in detg. the band-gap of perovskites. A systematic shift of the absorption band edge to shorter wavelengths is obsd. with increasing Br content in the perovskite films, which results in the decrement of the photocurrent. Nanorod like morphol. features are also obsd. for perovskite films with an iodide to bromide molar ratio of <0.7.
    9. 9
      Fedeli, P.; Gazza, F.; Calestani, D.; Ferro, P.; Besagni, T.; Zappettini, A.; Calestani, G.; Marchi, E.; Ceroni, P.; Mosca, R. Influence of the Synthetic Procedures on the Structural and Optical Properties of Mixed-Halide (Br,I) Perovskite Films J. Phys. Chem. C 2015, 119, 21304 DOI: 10.1021/acs.jpcc.5b03923
      There is no corresponding record for this reference.
    10. 10
      Ledinský, M.; Löper, P.; Niesen, B.; Holovský, J.; Moon, S.-J.; Yum, J.-H.; De Wolf, S.; Fejfar, A.; Ballif, C. Raman Spectroscopy of Organic Inorganic Halide Perovskites J. Phys. Chem. Lett. 2015, 6, 401 DOI: 10.1021/jz5026323
      10
      Raman Spectroscopy of Organic-Inorganic Halide Perovskites
      Ledinsky, Martin; Loper, Philipp; Niesen, Bjoern; Holovsky, Jakub; Moon, Soo-Jin; Yum, Jun-Ho; De Wolf, Stefaan; Fejfar, Antonin; Ballif, Christophe
      Journal of Physical Chemistry Letters (2015), 6 (3), 401-406CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      Micro-Raman spectroscopy provides laterally resolved microstructural information for a broad range of materials. In this Letter, we apply this technique to tri-iodide (CH3NH3PbI3), tribromide (CH3NH3PbBr3), and mixed iodide-bromide (CH3NH3PbI3-xBrx) org.-inorg. halide perovskite thin films and discuss necessary conditions to obtain reliable data. We explain how to measure Raman spectra of pristine CH3NH3PbI3 layers and discuss the distinct Raman bands that develop during moisture-induced degrdn. We also prove unambiguously that the final degrdn. products contain pure PbI2. Moreover, we describe CH3NH3PbI3-xBrx Raman spectra and discuss how the perovskite crystallog. symmetries affect the Raman band intensities and spectral shapes. On the basis of the dependence of the Raman shift on the iodide-to-bromide ratio, we show that Raman spectroscopy is a fast and nondestructive method for the evaluation of the relative iodide-to-bromide ratio.
    11. 11
      Gil-Escrig, L.; Miquel-Sempere, A.; Sessolo, M.; Bolink, H. J. Mixed Iodide-bromide Methylammonium Lead Perovskite-based Diodes for Light Emission and Photovoltaics J. Phys. Chem. Lett. 2015, 6, 3743 DOI: 10.1021/acs.jpclett.5b01716
      11
      Mixed Iodide-Bromide Methylammonium Lead Perovskite-based Diodes for Light Emission and Photovoltaics
      Gil-Escrig, Lidon; Miquel-Sempere, Araceli; Sessolo, Michele; Bolink, Henk J.
      Journal of Physical Chemistry Letters (2015), 6 (18), 3743-3748CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      Vacuum deposition techniques are used to prep. mixed iodide-bromide methylammonium lead perovskite diodes via an intermediate double layer of the pure iodide and bromide perovskites. The diodes lead to bright electroluminescence, whose emission spectra maxima shift from the IR toward the visible with increasing bromide content. When illuminated with AM1.5 simulated sunlight the devices function as efficient solar cells with power conversion efficiencies as high as 12.9%.
    12. 12
      Egger, D. A.; Edri, E.; Cahen, D.; Hodes, G. Perovskite Solar Cells: Do We Know What We Do Not Know? J. Phys. Chem. Lett. 2015, 6, 279 DOI: 10.1021/jz502726b
      12
      Perovskite Solar Cells: Do We Know What We Do Not Know?
      Egger, David A.; Edri, Eran; Cahen, David; Hodes, Gary
      Journal of Physical Chemistry Letters (2015), 6 (2), 279-282CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      There is no expanded citation for this reference.
    13. 13
      Hoke, E. T.; Slotcavage, D. J.; Dohner, E. R.; Bowring, A. R.; Karunadasa, H. I.; McGehee, M. D. Reversible Photo-induced Trap Formation in Mixed-halide Hybrid Perovskites for Photovoltaics Chem. Sci. 2015, 6, 613 DOI: 10.1039/C4SC03141E
      13
      Reversible photo-induced trap formation in mixed-halide hybrid perovskites for photovoltaics
      Hoke, Eric T.; Slotcavage, Daniel J.; Dohner, Emma R.; Bowring, Andrea R.; Karunadasa, Hemamala I.; McGehee, Michael D.
      Chemical Science (2015), 6 (1), 613-617CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      We report on reversible, light-induced transformations in (CH3NH3)Pb(BrxI1-x)3. Photoluminescence (PL) spectra of these perovskites develop a new, red-shifted peak at 1.68 eV that grows in intensity under const., 1-sun illumination in less than a minute. This is accompanied by an increase in sub-bandgap absorption at ∼1.7 eV, indicating the formation of luminescent trap states. Light soaking causes a splitting of X-ray diffraction (XRD) peaks, suggesting segregation into two cryst. phases. Surprisingly, these photo-induced changes are fully reversible; the XRD patterns and the PL and absorption spectra revert to their initial states after the materials are left for a few minutes in the dark. We speculate that photoexcitation may cause halide segregation into iodide-rich minority and bromide-enriched majority domains, the former acting as a recombination center trap. This instability may limit achievable voltages from some mixed-halide perovskite solar cells and could have implications for the photostability of halide perovskites used in optoelectronics.
    14. 14
      Niemann, R. G.; Kontos, A. G.; Palles, D.; Kamitsos, E. I.; Kaltzoglou, A.; Brivio, F.; Falaras, P.; Cameron, P. J. Halogen Effects on Ordering and Bonding of CH3NH3+ in CH3NH3PbX3 (X= Cl, Br, I) Hybrid Perovskites: A Vibrational Spectroscopic Study J. Phys. Chem. C 2016, 120, 2509 DOI: 10.1021/acs.jpcc.5b11256
      14
      Halogen Effects on Ordering and Bonding of CH3NH3+ in CH3NH3PbX3 (X = Cl, Br, I) Hybrid Perovskites: A Vibrational Spectroscopic Study
      Niemann, Ralf G.; Kontos, Athanassios G.; Palles, Dimitrios; Kamitsos, Efstratios I.; Kaltzoglou, Andreas; Brivio, Federico; Falaras, Polycarpos; Cameron, Petra J.
      Journal of Physical Chemistry C (2016), 120 (5), 2509-2519CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      This study reports Raman and IR spectra of hybrid org.-inorg. MAPbX3 perovskites (MA = CH3NH3, X = Cl, Br, I) and their mixed-halide derivs. Raman spectra were recorded at three laser wavelengths (514, 785, and 1064 nm) under on- and off-resonance conditions, as well as at room temp. and 100 K. The use of different excitation wavelengths allowed the unambiguous acquisition of "true" Raman spectra from the perovskites, without degrdn. or photoinduced structural changes. Low-frequency PbX vibrational modes were thoroughly identified by comparison of Raman and far-IR results. Red Raman frequency shifts for almost all MA vibrations from 200 to 3200 cm-1, and particularly intense for the torsional mode, were obsd. toward heavy halide derivs., indicative of strengthening the interaction between halides and the org. cation inside the inorg. cage. Different MA-X bonding schemes are evidenced by torsional mode pairs emerging in the orthorhombic phase. MAPbBr3 was further characterized by variable temp. Raman measurements (100-295 K). Broadening of the MA rocking mode slightly above the tetragonal I to II phase transition is connected with disorder of the MA cation. Our results advance the understanding of perovksite materials properties (ferroelec. domain formation, anomalous hysteresis) and their use as efficient light absorbers in solar cells.
    15. 15
      Xiao, Z.; Yuan, Y.; Shao, Y.; Wang, Q.; Dong, Q.; Bi, C.; Sharma, P.; Gruverman, A.; Huang, J. Giant Switchable Photovoltaic Effect in Organometal Trihalide Perovskite Devices Nat. Mater. 2015, 14, 193 DOI: 10.1038/nmat4150
      15
      Giant switchable photovoltaic effect in organometal trihalide perovskite devices
      Xiao, Zhengguo; Yuan, Yongbo; Shao, Yuchuan; Wang, Qi; Dong, Qingfeng; Bi, Cheng; Sharma, Pankaj; Gruverman, Alexei; Huang, Jinsong
      Nature Materials (2015), 14 (2), 193-198CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      Organolead trihalide perovskite (OTP) materials are emerging as naturally abundant materials for low-cost, soln.-processed and highly efficient solar cells. Here, we show that, in OTP-based photovoltaic devices with vertical and lateral cell configurations, the photocurrent direction can be switched repeatedly by applying a small elec. field of <1 V μm-1. The switchable photocurrent, generally obsd. in devices based on ferroelec. materials, reached 20.1 mA cm-2 under one sun illumination in OTP devices with a vertical architecture, which is four orders of magnitude larger than that measured in other ferroelec. photovoltaic devices. This field-switchable photovoltaic effect can be explained by the formation of reversible p-i-n structures induced by ion drift in the perovskite layer. The demonstration of switchable OTP photovoltaics and elec.-field-manipulated doping paves the way for innovative solar cell designs and for the exploitation of OTP materials in elec. and optically readable memristors and circuits.
    16. 16
      Yuan, Y.; Huang, J. Ion Migration in Organometal Trihalide Perovskite and Its Impact on Photovoltaic Efficiency and Stability Acc. Chem. Res. 2016, 49, 286 DOI: 10.1021/acs.accounts.5b00420
      16
      Ion Migration in Organometal Trihalide Perovskite and Its Impact on Photovoltaic Efficiency and Stability
      Yuan, Yongbo; Huang, Jinsong
      Accounts of Chemical Research (2016), 49 (2), 286-293CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      A review. Organometal trihalide perovskites (OTPs) are emerging as very promising photovoltaic materials because the power conversion efficiency (PCE) of OTP solar cells quickly rises and now rivals with that of single crystal silicon solar cells after only five-years research. Their prospects to replace silicon photovoltaics to reduce the cost of renewable clean energy are boosted by the low-temp. soln. processing as well as the very low-cost raw materials and relative insensitivity to defects. The flexibility, semitransparency, and vivid colors of perovskite solar cells are attractive for niche applications such as built-in photovoltaics and portable lightwt. chargers. However, the low stability of current hybrid perovskite solar cells remains a serious issue to be solved before their broad application. Among all those factors that affect the stability of perovskite solar cells, ion migration in OTPs may be intrinsic and cannot be taken away by device encapsulation.The presence of ion migration has received broad attention after the report of photocurrent hysteresis in OTP based solar cells. As suggested by much direct and indirect exptl. evidence, the ion migration is speculated to be the origin or an important contributing factor for many obsd. unusual phenomenon in OTP materials and devices, such as current-voltage hysteresis, switchable photovoltaic effect, giant dielec. const., diminished transistor behavior at room temp., photoinduced phase sepn., photoinduced self-poling effect, and elec.-field driven reversible conversion between lead iodide (PbI2) and methylammonium lead triiodide (MAPbI3). Undoubtedly thorough insight into the ion-migration mechanism is highly desired for the development of OTP based devices to improve intrinsic stability in the dark and under illumination. In this Account, we critically review the recent progress in understanding the fundamental science on ion migration in OTP based solar cells. We look into both theor. and expt. advances in answering these basic questions: Does ion migration occur and cause the photocurrent hysteresis in perovskite solar cells. What are the migrating ion species. How do ions migrate. How does ion migration impact the device efficiency and stability. How can ion migration be mitigated or eliminated. We also raise some questions that need to be understood and addressed in the future.
    17. 17
      Mosconi, E.; Amat, A.; Nazeeruddin, M. K.; Grätzel, M.; De Angelis, F. First Principles Modeling of Mixed Halde Organometal Perovskites for Photovoltaic Applications J. Phys. Chem. C 2013, 117, 13902 DOI: 10.1021/jp4048659
      There is no corresponding record for this reference.
    18. 18
      Yin, W.-J.; Yan, Y.; Wei, S.-H. Anomalous Alloy Properties in Mixed Halide Perovskites J. Phys. Chem. Lett. 2014, 5, 3625 DOI: 10.1021/jz501896w
      18
      Anomalous Alloy Properties in Mixed Halide Perovskites
      Yin, Wan-Jian; Yan, Yanfa; Wei, Su-Huai
      Journal of Physical Chemistry Letters (2014), 5 (21), 3625-3631CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      Engineering halide perovskite through mixing halogen elements, such as CH3NH3PbI3-xClx and CH3NH3PbI3-xBrx, is a viable way to tune its electronic and optical properties. Despite many emerging expts. on mixed halide perovskites, the basic electronic and structural properties of the alloys were not understood and some crucial questions remain, for example, how much Cl can be incorporated into CH3NH3PbI3 is still unclear. In this Letter, the authors chose CsPbX3 (X = I, Br, Cl) as an example and use a 1st-principle calcn. together with cluster-expansion methods to systematically study the structural, electronic, and optical properties of mixed halide perovskites and find that unlike conventional semiconductor alloys, they exhibit many anomalous alloy properties such as small or even neg. formation energies at some concns. and negligible or even neg. band gap bowing parameters at high temp. Further mixed-(I,Cl) perovskite is hard to form at temp. <625 K, whereas forming mixed-(Br,Cl) and (I,Br) alloys are easy at room temp.
    19. 19
      Onoda-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 DOI: 10.1016/0022-3697(90)90021-7
      19
      Calorimetric and IR spectroscopic studies of phase transitions in methylammonium trihaloplumbates(II)
      Onoda-Yamamuro, Noriko; Matsuo, Takasuke; Suga, Hiroshi
      Journal 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.
    20. 20
      Shannon, R. D. Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32, 751 DOI: 10.1107/S0567739476001551
      There is no corresponding record for this reference.
    21. 21
      Sher, A.; van Schilfgaarde, M.; Chen, A.-B.; Chen, W. Quasichemical Approximation in Binary Alloys Phys. Rev. B: Condens. Matter Mater. Phys. 1987, 36, 4279 DOI: 10.1103/PhysRevB.36.4279
      There is no corresponding record for this reference.
    22. 22
      Stringfellow, G. Calculation of Ternary and Quaternary III-V Phase Diagrams J. Cryst. Growth 1974, 27, 21 DOI: 10.1016/S0022-0248(74)80047-3
      22
      Calculation of ternary and quaternary III-V phase diagrams
      Stringfellow, G. B.
      Journal of Crystal Growth (1974), 27 (), 21-34CODEN: JCRGAE; ISSN:0022-0248.
      The models used to calc. binary and ternary III-V phase diagrams are reviewed. The simple solns. moel with Ω = a - bT is found to satisfactorily describe the liq. phase and the solid phase is adequately described using the regular soln. model. The DLP (delta lattice parameter) model of the solid, based on the concept that the bonding in alloys is detd. largely by the energy of the electrons, is found to be capable of predicting accurately the magnitudes of the solid interaction parameters knowing only the lattice parameters of the pure III-V compds. The simple soln. model with Ω = a - βT for the liq. and DLP model for the solid is then used in the calcn. of the quaternary III-V phase diagrams. One outcome of the calcn. is the establishment of a condition which can be used to check the consistency of the parameters ΔHF, TF, and Ω1 of the four solid III-V compds. bounding the solid phase field, against the soln. model. The agreement of the calcd. quaternary results with expt. in the GaxIn1-xAs1-y system is satisfactory. In the AlxGa1-xPyAs1-y system, the consistency condition is not satisfied, and thus the calcn. cannot agree with previous ternary calcns. for the (Al,Ga)As, (Al,Ga)P and Ga(As,P) systems simultaneously. Parameters were chosen so that good agreement is established with all except the (Al,Ga)P ternary.
    23. 23
      Yang, T.-Y.; Gregori, G.; Pellet, N.; Grätzel, M.; Maier, J. The Significance of Ion Conduction in a Hybrid Organic-Inorganic Lead-Iodide-Based Perovskite Photosensitizer Angew. Chem., Int. Ed. 2015, 54, 7905 DOI: 10.1002/anie.201500014
      23
      The Significance of Ion Conduction in a Hybrid Organic-Inorganic Lead Iodide-Based Perovskite Photosensitizer
      Yang, Tae-Youl; Gregori, Giuliano; Pellet, Norman; Graetzel, Michael; Maier, Joachim
      Angewandte Chemie, International Edition (2015), 54 (27), 7905-7910CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The success of perovskite solar cells has sparked excitement in the photovoltaic community not only because of unexpectedly high efficiencies but also because of the future potential ascribed to such cryst. absorber materials. Far from being exhaustively studied in terms of solid-state properties, these materials surprised by anomalies such as a huge apparent low-frequency dielec. const. and pronounced hysteretic current-voltage behavior. Methylammonium (but also formamidinium) iodoplumbates are mixed conductors with a large fraction of ion conduction because of I ions. In particular, the authors measure and model the stoichiometric polarization caused by the mixed conduction and demonstrate that the above anomalies can be explained by the build-up of stoichiometric gradients as a consequence of ion blocking interfaces. These findings provide insight into elec. charge transport in the hybrid org.-inorg. lead halide solar cells as well as into new possibilities of improving the photovoltaic performance by controlling the ionic disorder.
    24. 24
      Zhang, Y.; Liu, M.; Eperon, G. E.; Leijtens, T. C.; McMeekin, D.; Saliba, M.; Zhang, W.; De Bastiani, M.; Petrozza, A.; Herz, L. M. Charge Selective Contacts, Mobile Ions and Anomalous Hysteresis in Organic-Inorganic Perovskite Solar Cells Mater. Horiz. 2015, 2, 315 DOI: 10.1039/C4MH00238E
      24
      Charge selective contacts, mobile ions and anomalous hysteresis in organic-inorganic perovskite solar cells
      Zhang, Ye; Liu, Mingzhen; Eperon, Giles E.; Leijtens, Tomas C.; McMeekin, David; Saliba, Michael; Zhang, Wei; de Bastiani, Michele; Petrozza, Annamaria; Herz, Laura M.; Johnston, Michael B.; Lin, Hong; Snaith, Henry J.
      Materials Horizons (2015), 2 (3), 315-322CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
      High-efficiency perovskite solar cells typically employ an org.-inorg. metal halide perovskite material as light absorber and charge transporter, sandwiched between a p-type electron-blocking org. hole-transporting layer and an n-type hole-blocking electron collection titania compact layer. Some device configurations also include a thin mesoporous layer of TiO2 or Al2O3 which is infiltrated and capped with the perovskite absorber. Herein, we demonstrate that it is possible to fabricate planar and mesoporous perovskite solar cells devoid of an electron selective hole-blocking titania compact layer, which momentarily exhibit power conversion efficiencies (PCEs) of over 13%. This performance is however not sustained and is related to the previously obsd. anomalous hysteresis in perovskite solar cells. The "compact layer-free" meso-superstructured perovskite devices yield a stabilized PCE of only 2.7% while the compact layer-free planar heterojunction devices display no measurable steady state power output when devoid of an electron selective contact. In contrast, devices including the titania compact layer exhibit stabilized efficiency close to that derived from the current voltage measurements. We propose that under forward bias the perovskite diode becomes polarised, providing a beneficial field, allowing accumulation of pos. and neg. space charge near the contacts, which enables more efficient charge extn. This provides the required built-in potential and selective charge extn. at each contact to temporarily enable efficient operation of the perovskite solar cells even in the absence of charge selective n- and p-type contact layers. The polarisation of the material is consistent with long range migration and accumulation of ionic species within the perovskite to the regions near the contacts. When the external field is reduced under working conditions, the ions can slowly diffuse away from the contacts redistributing throughout the film, reducing the field asymmetry and the effectiveness of the operation of the solar cells. We note that in light of recent publications showing high efficiency in devices devoid of charge. selective contacts, this work reaffirms the abs. necessity to measure and report the stabilized power output under load when characterizing perovskite solar cells.
    25. 25
      Eames, C.; Frost, J. M.; Barnes, P. R. F.; O’Regan, B. C.; Walsh, A.; Islam, M. S. Ionic Transport in Hybrid Lead Iodide Perovskite Solar Cells Nat. Commun. 2015, 6, 7497 DOI: 10.1038/ncomms8497
      25
      Ionic transport in hybrid lead iodide perovskite solar cells
      Eames, Christopher; Frost, Jarvist M.; Barnes, Piers R. F.; O'Regan, Brian C.; Walsh, Aron; Islam, M. Saiful
      Nature Communications (2015), 6 (), 7497CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Solar cells based on org.-inorg. halide perovskites have recently shown rapidly rising power conversion efficiencies, but exhibit unusual behavior such as current-voltage hysteresis and a low-frequency giant dielec. response. Ionic transport has been suggested to be an important factor contributing to these effects; however, the chem. origin of this transport and the mobile species are unclear. Here, the activation energies for ionic migration in methylammonium lead iodide (CH3NH3PbI3) are derived from first principles, and are compared with kinetic data extd. from the current-voltage response of a perovskite-based solar cell. We identify the microscopic transport mechanisms, and find facile vacancy-assisted migration of iodide ions with an activation energy of 0.6 eV, in good agreement with the kinetic measurements. The results of this combined computational and exptl. study suggest that hybrid halide perovskites are mixed ionic-electronic conductors, a finding that has major implications for solar cell device architectures.
    26. 26
      Haruyama, J.; Sodeyama, K.; Han, L.; Tateyama, Y. First-Principles Study of Ion Diffusion in Perovskite Solar Cell Sensitizers J. Am. Chem. Soc. 2015, 137, 10048 DOI: 10.1021/jacs.5b03615
      26
      First-Principles Study of Ion Diffusion in Perovskite Solar Cell Sensitizers
      Haruyama, Jun; Sodeyama, Keitaro; Han, Liyuan; Tateyama, Yoshitaka
      Journal of the American Chemical Society (2015), 137 (32), 10048-10051CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Hysteresis in current-voltage curves has been an important issue for conversion efficiency evaluation and development of perovskite solar cells (PSCs). In this study, we explored the ion diffusion effects in tetragonal CH3NH3PbI3 (MAPbI3) and trigonal (NH2)2CHPbI3 (FAPbI3) by first-principles calcns. The calcd. activation energies of the anionic and cationic vacancy migrations clearly show that I- anions in both MAPbI3 and FAPbI3 can easily diffuse with low barriers of ca. 0.45 eV, comparable to that obsd. in ion-conducting materials. More interestingly, typical MA+ cations and larger FA+ cations both have rather low barriers as well, indicating that the cation mols. can migrate in the perovskite sensitizers when a bias voltage is applied. These results can explain the ion displacement scenario recently proposed by expts. With the dil. diffusion theory, we discuss that smaller vacancy concns. (higher crystallinity) and replacement of MA+ with larger cation mols. will be essential for suppressing hysteresis as well as preventing aging behavior of PSC photosensitizers.
    27. 27
      Azpiroz, J. M.; Mosconi, E.; Bisquert, J.; De Angelis, F. Defects Migration in Methylammonium Lead Iodide and their Role in Perovskite Solar Cells Operation Energy Environ. Sci. 2015, 8, 2118 DOI: 10.1039/C5EE01265A
      27
      Defect migration in methylammonium lead iodide and its role in perovskite solar cell operation
      Azpiroz, Jon M.; Mosconi, Edoardo; Bisquert, Juan; De Angelis, Filippo
      Energy & Environmental Science (2015), 8 (7), 2118-2127CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
      In spite of the unprecedented advance of organohalide lead perovskites in the photovoltaics scenario, many of the characteristics of this class of materials, including their slow photocond. response, solar cell hysteresis, and switchable photocurrent, remain poorly understood. Many exptl. hints point to defect migration as a plausible mechanism underlying these anomalous properties. By means of state-of-the-art first-principles computational analyses carried out on the tetragonal MAPbI3 (MA = methylammonium) perovskite and on its interface with TiO2, we demonstrate that iodine vacancies and interstitials may easily diffuse across the perovskite crystal, with migration activation energies as low as ∼0.1 eV. Under working conditions, iodine-related defects are predicted to migrate at the electrodes on very short time scales (<1 μs). MA and Pb vacancies, with calcd. activation barriers of ∼0.5 and 0.8 eV, resp., could be responsible for the slow response inherent to perovskites, with typical calcd. migration times of the order of tens of ms to minutes. By investigating realistic models of the perovskite/TiO2 interface we show that neg. charged defects, e.g. MA vacancies, close to the electron transport layer (TiO2 in our case) modify the perovskite electronic state landscape, hampering charge extn. at selective contacts, thus possibly contributing to the obsd. solar cell hysteresis. We further demonstrate the role of the electron transport layer in affecting the initial concn. of defects close to the selective contacts, highlighting how charge sepn. at the perovskite/TiO2 interface may further change the defect distribution. We believe that this work, identifying the mobile species in perovskite solar cells, their migration across the perovskite material, and their effect on the operational mechanism of the device, may pave the way for the development of new materials and solar cell architectures with improved and stabilized efficiencies.
    28. 28
      Hentz, O.; Zhao, Z.; Gradecak, S. Impacts of Ion Segregation on Local Optical Properties in Mixed Halide Perovskite Films Nano Lett. 2016, 16, 1485 DOI: 10.1021/acs.nanolett.5b05181
      28
      Impacts of Ion Segregation on Local Optical Properties in Mixed Halide Perovskite Films
      Hentz, Olivia; Zhao, Zhibo; Gradecak, Silvija
      Nano Letters (2016), 16 (2), 1485-1490CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Despite the recent astronomical success of org.-inorg. perovskite solar cells (PSCs), the impact of microscale film inhomogeneities on device performance remains poorly understood. In this work, we study CH3NH3PbI3 perovskite films using cathodoluminescence in scanning transmission electron microscopy and show that localized regions with increased cathodoluminescence intensity correspond to iodide-enriched regions. These observations constitute direct evidence that nanoscale stoichiometric variations produce corresponding inhomogeneities in film cathodoluminescence intensity. Moreover, we observe the emergence of high-energy transitions attributed to beam induced iodide segregation, which may mirror the effects of ion migration during PSC operation. Our results demonstrate that such ion segregation can fundamentally change the local optical and microstructural properties of org.-inorg. perovskite films in the course of normal device operation and therefore address the obsd. complex and unpredictable behavior in PSC devices.
    29. 29
      Shi, J.; Xu, X.; Zhang, H.; Luo, Y.; Li, D.; Meng, Q. Intrinsic Slow Charge Response in the Perovskite Solar Cells: Electron and Ion Transport Appl. Phys. Lett. 2015, 107, 163901 DOI: 10.1063/1.4934633
      There is no corresponding record for this reference.
    30. 30
      Teles, L. K.; Furthmüller, J.; Scolfaro, L. M. R.; Leite, J. R.; Bechstedt, F. First-principles Calculations of the Thermodynamic and Structural Properties of Strained InxGa1–xN and AlxGa1–xN Alloys Phys. Rev. B: Condens. Matter Mater. Phys. 2000, 62, 2475 DOI: 10.1103/PhysRevB.62.2475
      30
      First-principles calculations of the thermodynamic and structural properties of strained InxGa1-xN and AlxGa1-xN alloys
      Teles, L. K.; Furthmuller, J.; Scolfaro, L. M. R.; Leite, J. R.; Bechstedt, F.
      Physical Review B: Condensed Matter and Materials Physics (2000), 62 (4), 2475-2485CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
      We present first-principles calcns. of the thermodn. and structural properties of cubic InxGa1-xN and AlxGa1-xN alloys. They are based on the generalized quasi-chem. approach to disorder and compn. effects and a pseudopotential-plane-wave approxn. for the total energy. The cluster treatment is generalized to study the influence of biaxial strain. We find a remarkable suppression of phase sepn. in InxGa1-xN.
    31. 31
      Schleife, A.; Eisenacher, M.; Rödl, C.; Fuchs, F.; Furthmüller, J.; Bechstedt, F. Ab initio Description of Heterostructural Alloys: Thermodynamic and Structural Properties of MgxZn1–xO and CdxZn1–xO Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 81, 245210 DOI: 10.1103/PhysRevB.81.245210
      There is no corresponding record for this reference.
    32. 32
      Kohn, W.; Sham, L. J. Self-consistent Equations Including Exchange and Correlation Effects Phys. Rev. 1965, 140, A1133 DOI: 10.1103/PhysRev.140.A1133
      There is no corresponding record for this reference.
    33. 33
      Frost, J. M.; Butler, K. T.; Brivio, F.; Hendon, C. H.; van Schilfgaarde, M.; Walsh, A. Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells Nano Lett. 2014, 14, 2584 DOI: 10.1021/nl500390f
      33
      Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells
      Frost, Jarvist M.; Butler, Keith T.; Brivio, Federico; Hendon, Christopher H.; van Schilfgaarde, Mark; Walsh, Aron
      Nano Letters (2014), 14 (5), 2584-2590CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      The performance of organometallic perovskite solar cells has rapidly surpassed that of both conventional dye-sensitized and org. photovoltaics. High-power conversion efficiency can be realized in both mesoporous and thin-film device architectures. The authors address the origin of this success in the context of the materials chem. and physics of the bulk perovskite as described by electronic structure calcns. In addn. to the basic optoelectronic properties essential for an efficient photovoltaic device (spectrally suitable band gap, high optical absorption, low carrier effective masses), the materials are structurally and compositionally flexible. As the authors show, hybrid perovskites exhibit spontaneous elec. polarization; the authors also suggest ways in which this can be tuned through judicious choice of the org. cation. The presence of ferroelec. domains will result in internal junctions that may aid sepn. of photoexcited electron and hole pairs, and redn. of recombination through segregation of charge carriers. The combination of high dielec. const. and low effective mass promotes both Wannier-Mott exciton sepn. and effective ionization of donor and acceptor defects. The photoferroic effect could be exploited in nanostructured films to generate a higher open circuit voltage and may contribute to the current-voltage hysteresis obsd. in perovskite solar cells.
    34. 34
      Brivio, F.; Frost, J. M.; Skelton, J. M.; Jackson, A. J.; Weber, O. J.; Weller, M. T.; Goni, A. R.; Leguy, A. M. A.; Barnes, P. R. F.; Walsh, A. Lattice Dynamics and Vibrational Spectra of the Orthorhombic, Tetragonal, and Cubic Phases of Methylammonium Lead Iodide Phys. Rev. B: Condens. Matter Mater. Phys. 2015, 92, 144308 DOI: 10.1103/PhysRevB.92.144308
      34
      Lattice dynamics and vibrational spectra of the orthorhombic, tetragonal, and cubic phases of methylammonium lead iodide
      Brivio, Federico; Frost, Jarvist M.; Skelton, Jonathan M.; Jackson, Adam J.; Weber, Oliver J.; Weller, Mark T.; Goni, Alejandro R.; Leguy, Aurelien M. A.; Barnes, Piers R. F.; Walsh, Aron
      Physical Review B: Condensed Matter and Materials Physics (2015), 92 (14), 144308/1-144308/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      The hybrid halide perovskite CH3NH3PbI3 exhibits a complex structural behavior, with successive transitions between orthorhombic, tetragonal, and cubic polymorphs around 165 and 327 K. Herein we report first-principles lattice dynamics (phonon spectrum) for each phase of CH3NH3PbI3. The equil. structures compare well to solns. of temp.-dependent powder neutron diffraction. By following the normal modes, we calc. IR and Raman intensities of the vibrations, and compare them to the measurement of a single crystal where the Raman laser is controlled to avoid degrdn. of the sample. Despite a clear sepn. in energy between low-frequency modes assocd. with the inorg. (PbI3-)n network and high-frequency modes of the org. CH3NH3+ cation, significant coupling between them is found, which emphasizes the interplay between mol. orientation and the corner-sharing octahedral networks in the structural transformations. Soft modes are found at the boundary of the Brillouin zone of the cubic phase, consistent with displacive instabilities and anharmonicity involving tilting of the PbI6 octahedra around room temp.
    35. 35
      Grau-Crespo, R.; Hamad, S.; Catlow, C. R. A.; de Leeuw, N. H. Symmetry-adapted Configurational Modelling of Fractional Site Occupancy in Solids J. Phys.: Condens. Matter 2007, 19, 256201 DOI: 10.1088/0953-8984/19/25/256201
      35
      Symmetry-adapted configurational modelling of fractional site occupancy in solids
      Grau-Crespo, R.; Hamad, S.; Catlow, C. R. A.; de Leeuw, N. H.
      Journal of Physics: Condensed Matter (2007), 19 (25), 256201/1-256201/16CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)
      A methodol. is presented, which reduces the no. of site-occupancy configurations to be calcd. when modeling site disorder in solids, by taking advantage of the crystal symmetry of the lattice. Within this approach, two configurations are considered equiv. when they are related by an isometric operation; a trial list of possible isometric transformations is provided by the group of symmetry operators in the parent structure, which is used to generate all configurations via at. substitutions. We have adapted the equations for configurational statistics to operate in the reduced configurational space of the independent configurations. Each configuration in this space is characterized by its reduced energy, which includes not only its energy but also a contribution from its degeneracy in the complete configurational space, via an entropic term. The new computer program SOD (site-occupancy disorder) is presented, which performs this anal. in systems with arbitrary symmetry and any size of supercell. As a case study we use the distribution of cations in iron antimony oxide FeSbO4, where we also introduce some general considerations for the modeling of site-occupancy disorder in paramagnetic systems.
    36. 36
      Leguy, A.; Hu, Y.; Campoy-Quiles, M.; Alonso, M. I.; Weber, O. J.; Azarhoosh, P.; van Schilfgaarde, M.; Weller, M. T.; Bein, T.; Nelson, J. The Reversible Hydration of CH3NH3PbI3 in Films, Single Crystals and Solar Cells Chem. Mater. 2015, 27, 3397 DOI: 10.1021/acs.chemmater.5b00660
      36
      Reversible Hydration of CH3NH3PbI3 in Films, Single Crystals, and Solar Cells
      Leguy, Aurelien M. A.; Hu, Yinghong; Campoy-Quiles, Mariano; Alonso, M. Isabel; Weber, Oliver J.; Azarhoosh, Pooya; van Schilfgaarde, Mark; Weller, Mark T.; Bein, Thomas; Nelson, Jenny; Docampo, Pablo; Barnes, Piers R. F.
      Chemistry of Materials (2015), 27 (9), 3397-3407CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Solar cells composed of methylammonium lead iodide perovskite (MAPI) are notorious for their sensitivity to moisture. It is shown that hydrated crystal phases are formed when MAPI is exposed to water vapor at room temp. and these phase changes are fully reversed when the material is subsequently dried. The reversible formation of CH3NH3PbI3·H2O followed by (CH3NH3)4PbI6·2H2O (upon long exposure times) was obsd. using time-resolved XRD and ellipsometry of thin films prepd. using "solvent engineering", single crystals, and state-of-the-art solar cells. In contrast to water vapor, the presence of liq. water results in the irreversible decompn. of MAPI to form PbI2. MAPI changes from dark brown to transparent on hydration; the precise optical consts. of CH3NH3PbI3·H2O formed on single crystals were detd., with a bandgap at 3.1 eV. Using the single-crystal optical consts. and thin-film ellipsometry measurements, the time-dependent changes to MAPI films exposed to moisture were modeled. The results suggest that the monohydrate phase forms independent of the depth in the film, suggesting rapid transport of water mols. along grain boundaries. Vapor-phase hydration of an unencapsulated solar cell (initially Jsc ≈ 19 mA cm-2 and Voc ≈ 1.05 V at 1 sun) resulted in more than a 90% drop in short-circuit photocurrent and ∼200 mV loss in open-circuit potential; however, these losses were fully reversed after the device was exposed to dry nitrogen for 6 h. Hysteresis in the current-voltage characteristics was significantly increased after this dehydration, which may be related to changes in the defect d. and morphol. of MAPI following recrystn. from the hydrate. Based on the observations, it is suggested that irreversible decompn. of MAPI in the presence of water vapor only occurs significantly once a grain has been fully converted to the monohydrate phase.
    37. 37
      Bakulin, A. A.; Selig, O.; Bakker, H. J.; Rezus, Y. L. A.; Müller, C.; Glaser, T.; Lovrincic, R.; Sun, Z.; Chen, Z.; Walsh, A. Real-Time Observation of Organic Cation Reorientation in Methylammonium Lead Iodide Perovskites J. Phys. Chem. Lett. 2015, 6, 3663 DOI: 10.1021/acs.jpclett.5b01555
      37
      Real-Time Observation of Organic Cation Reorientation in Methylammonium Lead Iodide Perovskites
      Bakulin, Artem A.; Selig, Oleg; Bakker, Huib J.; Rezus, Yves L. A.; Mueller, Christian; Glaser, Tobias; Lovrincic, Robert; Sun, Zhenhua; Chen, Zhuoying; Walsh, Aron; Frost, Jarvist M.; Jansen, Thomas L. C.
      Journal of Physical Chemistry Letters (2015), 6 (18), 3663-3669CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      The introduction of a mobile and polarized org. moiety as a cation in 3D Pb-iodide perovskites brings fascinating optoelectronic properties to these materials. The extent and the time scales of the orientational mobility of the org. cation and the mol. mechanism behind its motion remain unclear, with different exptl. and computational approaches providing very different qual. and quant. description of the mol. dynamics. Ultrafast 2D vibrational spectroscopy of methylammonium (MA) Pb iodide was used to directly resolve the rotation of the org. cations within the MAPbI3 lattice. The results reveal 2 characteristic time consts. of motion. Using ab initio mol. dynamics simulations, the authors identify these as a fast (∼300 fs) wobbling-in-a-cone motion around the crystal axis and a relatively slow (∼3 ps) jump-like reorientation of the mol. dipole with respect to the iodide lattice. The obsd. dynamics are essential for understanding the electronic properties of perovskite materials.
    38. 38
      Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab initio Total-energy Calculations Using a Plane-wave Basis Set Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169 DOI: 10.1103/PhysRevB.54.11169
      38
      Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set
      Kresse, G.; Furthmueller, J.
      Physical Review B: Condensed Matter (1996), 54 (16), 11169-11186CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
      The authors present an efficient scheme for calcg. the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrixes will be discussed. This approach is stable, reliable, and minimizes the no. of order Natoms3 operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special "metric" and a special "preconditioning" optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calcns. It will be shown that the no. of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order Natoms2 scaling is found for systems contg. up to 1000 electrons. If we take into account that the no. of k points can be decreased linearly with the system size, the overall scaling can approach Natoms. They have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable.
    39. 39
      Perdew, J. P.; Ruzsinszky, A.; Csonka, G. I.; Vydrov, O. A.; Scuseria, G. E.; Constantin, L. A.; Zhou, X.; Burke, K. Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces Phys. Rev. Lett. 2008, 100, 136406 DOI: 10.1103/PhysRevLett.100.136406
      39
      Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces
      Perdew, John P.; Ruzsinszky, Adrienn; Csonka, Gabor I.; Vydrov, Oleg A.; Scuseria, Gustavo E.; Constantin, Lucian A.; Zhou, Xiaolan; Burke, Kieron
      Physical Review Letters (2008), 100 (13), 136406/1-136406/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      Popular modern generalized gradient approxns. are biased toward the description of free-atom energies. Restoration of the first-principles gradient expansion for exchange over a wide range of d. gradients eliminates this bias. We introduce a revised Perdew-Burke-Ernzerhof generalized gradient approxn. that improves equil. properties of densely packed solids and their surfaces.
    40. 40
      Blöchl, P. E. Projector Augmented-wave Method Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 50, 17953 DOI: 10.1103/PhysRevB.50.17953
      40
      Projector augmented-wave method
      Blochl
      Physical review. B, Condensed matter (1994), 50 (24), 17953-17979 ISSN:0163-1829.
      There is no expanded citation for this reference.