Atomic-Level Description of Thermal Fluctuations in Inorganic Lead Halide PerovskitesClick to copy article linkArticle link copied!
- Oliviero CannelliOliviero CannelliLaboratory of Ultrafast Spectroscopy (LSU) and Lausanne Centre for Ultrafast Science (LACUS), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, SwitzerlandMore by Oliviero Cannelli
- Julia WiktorJulia WiktorDepartment of Physics, Chalmers University of Technology, SE-412 96 Gothenburg, SwedenMore by Julia Wiktor
- Nicola ColonnaNicola ColonnaLaboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen-PSI, SwitzerlandNational Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, SwitzerlandMore by Nicola Colonna
- Ludmila LeroyLudmila LeroyLaboratory of Ultrafast Spectroscopy (LSU) and Lausanne Centre for Ultrafast Science (LACUS), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, SwitzerlandLabCri, Departamento de Física, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte, BrazilMore by Ludmila Leroy
- Michele PuppinMichele PuppinLaboratory of Ultrafast Spectroscopy (LSU) and Lausanne Centre for Ultrafast Science (LACUS), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, SwitzerlandMore by Michele Puppin
- Camila Bacellar
- Ilia Sadykov
- Franziska KriegFranziska KriegInstitute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, SwitzerlandLaboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, SwitzerlandMore by Franziska Krieg
- Grigory SmolentsevGrigory SmolentsevPaul Scherrer Institute (PSI), CH-5232 Villigen, SwitzerlandMore by Grigory Smolentsev
- Maksym V. KovalenkoMaksym V. KovalenkoInstitute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, SwitzerlandLaboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, SwitzerlandMore by Maksym V. Kovalenko
- Alfredo PasquarelloAlfredo PasquarelloChaire de Simulation à l’Echelle Atomique (CSEA), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, SwitzerlandMore by Alfredo Pasquarello
- Majed Chergui*Majed Chergui*Email: [email protected]Laboratory of Ultrafast Spectroscopy (LSU) and Lausanne Centre for Ultrafast Science (LACUS), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, SwitzerlandMore by Majed Chergui
- Giulia F. Mancini*Giulia F. Mancini*Email: [email protected]Laboratory for Ultrafast X-ray and Electron Microscopy (LUXEM), Department of Physics, University of Pavia, I-27100 Pavia, ItalyMore by Giulia F. Mancini
Abstract
A comprehensive microscopic description of thermally induced distortions in lead halide perovskites is crucial for their realistic applications, yet still unclear. Here, we quantify the effects of thermal activation in CsPbBr3 nanocrystals across length scales with atomic-level precision, and we provide a framework for the description of phase transitions therein, beyond the simplistic picture of unit-cell symmetry increase upon heating. The temperature increase significantly enhances the short-range structural distortions of the lead halide framework as a consequence of the phonon anharmonicity, which causes the excess free energy surface to change as a function of temperature. As a result, phase transitions can be rationalized via the soft-mode model, which also describes displacive thermal phase transitions in oxide perovskites. Our findings allow to reconcile temperature-dependent modifications of physical properties, such as changes in the optical band gap, that are incompatible with the perovskite time- and space-average structures.
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The implementation of lead halide perovskites as active medium in photovoltaic and optoelectronic devices is currently hindered by their relatively poor long-term stability. (1,2) Indeed, despite their promising performances, (3,4) these materials suffer from degradation under operative conditions, caused by external factors such as oxygen, moisture, and light. (5−7) Composition and structural instabilities were also observed, due to ion migration, (8) phase segregation, (9) and thermal heat effects. (10) Even though effective strategies to mitigate some of these issues are already under development, as in the case of degradation due to moisture, (11,12) solutions to other forms of instabilities still require additional investigation. Specifically, thermal and optical stimuli, which represent two forms of functional activation respectively exploited for thermoelectrics (13−15) and optoelectronics, (16,17) are also possible sources of degradation.
The perovskite structural instabilities are closely related to the peculiar flexibility of the Pb−X (X = Cl–, Br–, I–) lead halide framework, characterized by pronounced lability and phonon anharmonicity. (18−24) The deformable lattice results in small free energy formation of anion vacancies and low activation energy for vacancy-mediated transport, implying intrinsic high anion mobility (25) and causing reversible phase separation when multihalide perovskites are exposed to continuous illumination. (9)
The study of a photoexcited system requires to disentangle optically induced electronic effects from possible thermal ones. In a recent work on CsPbBr3 nanocrystals (NCs), (26) we demonstrated that thermal effects are not significant in the photoinduced response, which is characterized by polaronic lattice distortions that we specifically quantified with atomic-level precision. Here, we focus on the characterization of the temperature (T)-induced response of the CsPbBr3 NCs in a temperature range relevant for optoelectronic applications. We therefore provide a comprehensive description of CsPbBr3 perovskite nanocrystals dynamics, and we clarify that lattice flexibility is underpinning fundamentally different responses upon photo- or thermal activation.
The structure of CsPbBr3 consists of a Pb–Br inorganic sublattice in which the Pb2+ ions are surrounded by 6 Br– anions, making a framework of corner-sharing octahedra. The cuboctahedral voids left in the crystal are filled by the Cs+ ions, creating a complementary sublattice where the cations undergo a free rattling motion. (19) In single crystals, the phase diagram of this system was determined by neutron and X-ray diffraction (XRD) studies, which identifies phases of increasing symmetry upon temperature rise: orthorhombic Pnma (T < 88 °C), tetragonal P4/mbm (88 °C < T < 130 °C), and cubic Pm3̅m (T > 130 °C). (27,28) In recent years, this simple description in terms of transformations of ideal lattices across the phase diagram was questioned, even though the presence of structural disorder at high temperatures was already suggested in the seminal work of Møller on inorganic lead halide perovskites single crystals. (29) Thermal distortions of the cubic unit cells were shown in both methylammonium (MA+) and cesium lead bromide single crystals through first-principles molecular dynamics (MD) and low-frequency Raman scattering. (22) T-induced rotational disorder of lead halide octahedra was also observed in a high energy resolution inelastic X-ray scattering (HERIX) and pair distribution function (PDF) study on MAPbI3 single crystals at 350 K, ascribing the effect to the phonon anharmonicity of the Pb–I cage. (20)
In nanostructured perovskites, the scenario is even more complex, as many physical properties are influenced by the dimensionality of the structure. XRD measurements on CsPbBr3 perovskite NCs showed the impact of the system’s size on the phase diagram, with phase transitions observed at lower temperatures with respect to their bulk counterpart, in the ranges T = 50–59 °C and T = 108–117 °C, ascribed to the unit cell changes orthorhombic-tetragonal and tetragonal-cubic, respectively. (21) Conversely, approaches beyond standard Rietveld refinement methods highlighted the structural defectiveness of inorganic lead halide NCs. This was associated with orthorhombic twinned subdomains both at room and higher temperatures, (23) suggesting that multiple structural configurations are copresent in the system. The dimensionality of the NCs also affects the thermal transport, which changes from the diffusive regime to the ballistic limit when the size of the structure is smaller than the inelastic phonons mean-free path of the semiconductor, (30) and it is routinely exploited to tune the band gap and photoluminescence spectra of lead halide perovskites. Furthermore, ligand-capping strategies, which are often employed to enhance the NC system’s stability, (12,31) also modify the charge carriers relaxation (32) and opto-mechanical properties of these structures. (33) As a result, a direct comparison between bulk and NCs is often misleading.
Even though a large variety of experimental and computational methods have been employed to investigate the flexibility of the lead halide structure, a unified picture simultaneously describing T-induced changes in the short-range and in the long-range is still missing. Additionally, the reported static and dynamic local disorder is in contrast with the assignment of highly ordered phases in the long-range, especially at high temperatures, raising questions about the phase diagrams proposed in early works (27,28,34) and its validity to describe key properties of the system. Some studies ascribed the perovskites high-temperature phase to an apparent cubic structure resulting from the statistical average of disordered local structures, (20,22,23) but the disorder itself was never fully reconciled with the presence of well-defined phase transition temperatures. Conversely, Monte Carlo simulations at finite-temperatures assigned the qualitative features of the phase transitions of CsPbBr3 to pure thermal lattice activation; (35) however, the authors did not benchmark their theoretical results against experimental observables.
Here, we present a correlative characterization of the short-range and long-range structures in T-activated CsPbBr3 NCs. We performed T-dependent measurements of Br K-edge X-ray absorption near edge structure (XANES) spectroscopy and powder XRD on CsPbBr3 NCs in the 25–140 °C range, i.e., across the phase diagram of the nanostructured material, and compare them to ab initio MD calculations as a function of temperature. The XANES and XRD observables were computed as averages over several configurations extracted from the MD trajectory, with the XANES spectra additionally including core hole final state effects. This approach goes beyond standard structural refinement methods and fully accounts for the statistical fluctuations of the lattice structure.
The XANES shows that T-dependent short-range changes cannot be accurately described by average lattice structures from PDF refinement. Instead, the system dynamically adopts multiple local configurations that are characterized by pronounced structural deformations with respect to the ideal symmetries. In the high temperature phase, these lattice distortions have a magnitude comparable to those of the low-symmetry orthorhombic phase, but the stronger thermal fluctuations cause the long-range periodicity of the lattice to break, reproducing the T-dependent changes of the XRD experiment. Our observations are ascribed to the intrinsic phonon anharmonicity of the lead halide sublattice and are rationalized in terms of displacive thermal phase transitions via the soft-mode model. (36) This conceptual framework provides a thorough description of the physical properties of the system upon thermal heating, as in the case of band gap increase, (37) which cannot be captured by scenarios that preserve high symmetry lattice structures at the local scale.
Moreover, these results highlight the difference between thermal and light-induced structural responses in CsPbBr3 perovskites, the former being intrinsically random in nature and the latter selectively driven by electron–phonon coupling. (26) The deeper understanding of the perovskite responses upon different stimuli will open new opportunities for manipulating and stabilizing the lattice structure in realistic applications.
T-dependent XANES and XRD measurements were performed at the SuperXAS beamline at the Swiss Light Source (SLS) of the Paul Scherrer Institute. The concept of the experiment is depicted in Figure 1a. The sample consists of a powder of long-chain zwitterion-capped CsPbBr3 dry perovskite NCs with cuboidal shape (side length 11.9 ± 2.2 nm) and high photoluminescence quantum yield. (31) The sample was located in a thermostated cell holder between two 0.254 mm-thick graphite layers, and the internal temperature of the cell was calibrated and monitored throughout the experiment with a thermocouple.
Figure 1
Figure 1. (a) Multiscale probing of thermally induced changes in CsPbBr3 perovskite nanocrystals: schematic layout of the experiment. T-dependent XRD and XANES measurements were conducted in parallel on CsPbBr3 dry nanocrystals, respectively at 12.9 keV and at the Br K-edge (13.450–13.570 keV). Courtesy of Balázs Őrley. CsPbBr3 crystal structures: (b) Pm3̅m cubic and (c) Pnma orthorhombic unit cell graphics, each with a schematic for the tilting of the inorganic framework. In the orthorhombic phase, the ordered tilting of the PbBr6 octahedra causes the doubling of the unit cell constant along the crystallographic c-axis. (50)
T-dependent XRD measurements were performed using a monochromatic 12.9 keV X-ray beam in transmission geometry, with a sample–detector distance of 24.1 cm. The transmitted diffraction signal was acquired using a Pilatus 100k 2D detector (94965 pixels, 172 × 172 μm2 pixel area) and then azimuthally averaged in the 1.3–2.8 Å–1Q-range to obtain the radial averaged intensity I(Q)
Ab initio MD simulations based on density functional theory (DFT) were performed using the CP2K package. (39) The Perdew–Burke–Ernzerhof (PBE) functional (40) was used to describe the exchange-correlation energy. Three different MD simulations, lasting for 10–16 ps and using a time step of 5 fs, were carried out in the isobaric (NpT) ensemble. In the runs, the initial shape of the cell was kept constant, while the volume of the cell was allowed to fluctuate. One MD calculation was run at 27 °C (300 K) with the orthorhombic geometry as initial condition. At 130 °C (403 K), two simulations were run, one initialized with the cubic and one with the orthorhombic geometry. These structures were chosen to monitor the thermal dynamics of the system in its lowest and highest structural phases. For the high-temperature simulations, the two different starting geometries were considered in order to evaluate the impact of the initial conditions on the computation. Simulations were carried out in supercells containing 1080 atoms, which corresponds to the 6 × 6 × 6 repetition of the unitary cubic cell. The Brillouin zone was sampled solely at the Γ point. The first 5 ps of the simulations were considered as equilibration and excluded from the statistics. The mean XRD I(Q) profiles were calculated averaging the scattering intensities predicted by VESTA (38) for instantaneous structures separated by 0.75 ps extracted from the MD trajectories. Three additional MD simulations, with the same parameters and starting conditions, were also performed for smaller supercells (320 atoms, corresponding to the 4 × 4 × 4 repetition of the unitary cubic cell) to generate structures for the computationally demanding XANES simulations.
XANES spectra were computed performing first-principles DFT calculations using the Quantum Espresso distribution. (41,42) The exchange-correlation effects were described using the PBE functional, (40) and the ultrasoft pseudopotentials from the PS-library (43) were employed to model the electron–ion interaction. Br K-edge spectra were simulated with the XSpectra code (44,45) within the excited-electron plus core-hole (XCH) approximation. (46) Calculations were based on 320-atoms structures obtained from ab initio MD simulations in the CP2K package, (39) corresponding to the 4 × 4 × 4 repetition of the unitary cubic cell. MD calculations were run at 27 °C (300 K) for an initial orthorhombic geometry and at 130 °C (403 K) for initial orthorhombic and cubic geometries. For each MD simulation, 5 structures corresponding to 5 different time delays of the MD trajectory were considered. For each time delay, 10 separate XCH calculations were performed with a core hole placed on a randomly chosen Br site of the supercell, for which the Br K-edge spectrum was computed. The final Br K-edge spectra result from the average of 10 Br sites in each of the 5 MD structures, for a total of 50 spectra per MD simulation. Additional XCH simulations were performed for 160-atoms supercells which, were built starting from either the ideal orthorhombic or cubic unit cells, using the atomic coordinates reported in the literature from PDF refinements at 22 and 160 °C, respectively. (21) For each nonequivalent Br site, separate XCH calculations were performed, and the average Br K-edge XANES spectrum was computed. Details about the experimental and computational methods are described in the SI.
Figure 2 shows XAS and XRD results (experimental - top, and theoretical - bottom) obtained for the CsPbBr3 system as a function of temperature. The Br K-edge experimental spectra (Figure 2a) collected for the NCs at 25 °C (dashed gray) and 120 °C (dashed red) show that the XANES spectrum is affected by the temperature increase both at pre-edge energies (47) and above the edge, which represents the ionization limit. Above the edge, the XANES spectrum is caused by single and multiple scattering events of the photoelectron emitted by the Br atoms against the neighboring atoms, and it contains information about bond angles and bond distances between the probed site and its nearest-neighbors. (48,49) The XANES traces were scaled by their total areas, and they exhibit a first peak at the Br edge (the so-called white line, at 13.472 keV), related to the Br 1s-4p electronic transition, followed by post-edge modulations peaked at 13.4875 and 13.510 keV. The temperature rise from 25 to 120 °C induces an intensity decrease of the main peaks and an intensity increase of the local minima, with an overall broadening of the spectral features. This is best visualized in Figure 2b where the difference between the 120 °C and the 25 °C experimental XANES spectra is reported in dashed gray. The data show a broad negative feature in the rising-edge region at energies 13.466–13.478 keV, with a global minimum at the edge position of 13.472 keV. A pronounced modulation is also observed up to 50 eV above the edge, with damped positive and negative features respectively peaked in the local minima and maxima of the steady-state spectra.
Figure 2
Figure 2. Correlative short- and long-range T-dependent structural characterization of CsPbBr3. (a) Experimental Br K-edge XANES spectra of CsPbBr3 NCs at 25 °C (dashed gray) and at 120 °C (dashed red), ab initio XANES spectra for the pristine orthorhombic and cubic structures obtained from a PDF refinement of XRD data (21) (dotted blue and dotted red, respectively), and ab initio XANES spectra for the MD simulations at 27 °C (orthorhombic starting symmetry, gray) and 130 °C (orthorhombic and cubic starting symmetries, yellow and red, respectively). All spectra were scaled by their underlying areas and vertically offset. (b) Br K-edge XANES differences for 120 °C minus 25 °C (experiment, dashed gray), pristine cubic minus pristine orthorhombic from PDF refinements (dotted blue) and the difference between the linear combinations of cubic 130 °C and orthorhombic 130 °C minus orthorhombic 27 °C MD simulations. The curves were obtained considering different coefficients of the cubic 130 °C and orthorhombic 130 °C MD spectra, from 100% cubic (red) to 100% orthorhombic (yellow). A 3-point adjacent averaging of the energy axis was performed for the experimental thermal difference, whereas the simulated spectral differences were multiplied by a factor ×0.30 (MD) and ×0.15 (pristine), the latter also being vertically shifted, to enable a straightforward comparison with the experiment. (c) Experimental XRD I(Q) profiles of CsPbBr3 NCs as a function of the temperature from 25 to 140 °C. The sharp feature at 1.827 Å–1 originates from the graphite peak enclosing the sample (blue curve). The shaded gray areas mark the region of the (i) and (iii) superlattice peaks, which disappear upon temperature increase. (d) XRD I(Q) profiles predicted from the MD simulations at 27 °C with orthorhombic starting geometry (gray), 130 °C with orthorhombic starting geometry (yellow) and 130 °C with cubic starting geometry (red). The shaded gray areas highlight the (i), (ii), and (iii) superlattice peaks. Inset: zoom into the 1.55–1.94 Å–1 region of the superlattice peaks. In the legend of each panel, “ortho” stands for “orthorhombic”.
Figure 2a also shows the XANES spectra computed with ab initio simulation for MD calculations at 27 °C for an orthorhombic starting geometry (full gray curve) and at 130 °C for orthorhombic and cubic initial configurations (respectively, full yellow and full red curves). Although the two initial symmetries for the MD simulations at 130 °C are different, at this temperature the thermal activation lifts the original symmetry of the structure and dynamically distorts the lattice. This is consistent with the statistical evolution of the Pb–Br–Pb angle tilting over time (Figure S10) and the displacements of Cs, Pb, and Br sites with respect to their average positions (Figure S12), which show that the CsPbBr3 lattice is characterized by pronounced local distortions and becomes dynamically more active with temperature. The minor differences in the predictions of the two calculations can be ascribed to the different boundary conditions imposed to the supercell for the two starting symmetries. We additionally show computations for the two pristine orthorhombic and cubic lattice structures (respectively, dotted blue and dotted red) as obtained from a PDF analysis of T-dependent XRD data reported in the literature. (21)
In all simulations, core hole final state effects were included, thus the difference between the XANES spectra of the MD and pristine structures lies on the presence or absence of local thermal fluctuations in the lattice. Specifically, the predictions of the MD simulations correspond to the statistical average of multiple XANES spectra of Br sites in different local environments. Instead, the calculations for the pristine structures reflect the XANES spectrum of a single time- and space-averaged configuration that preserves the translational symmetry in the long- and short-range, respectively orthorhombic (room temperature) or cubic (high temperature).
All simulations reproduce the Br K-edge main features; intensity deviations with respect to the experiment are due to systematic errors of the calculations which, however, cancel out when performing spectral differences between computed XANES spectra (Figure 2b). The two MD-simulated XANES traces at 130 °C have similar line shapes, both showing a blue shift of the rising edge and an intensity reduction of the main peaks at the energies 13.472 keV, 13.486, and 13.506 keV with respect to the MD simulation at 27 °C. A corresponding increase of the XANES intensity occurs at the energy of the local minima, in agreement with the experiment. Conversely, the comparison of the XANES spectra for the pristine cubic and orthorhombic structures shows that the former is significantly sharper than the latter and is characterized by one additional feature at 13.498 keV, in net contrast with the experiment.
The XANES differences for the orthorhombic and cubic MD simulations at 130 °C minus the orthorhombic MD simulation at 27 °C are shown in Figure 2b in yellow and red, respectively. In the same figure, we also present the curves obtained subtracting the orthorhombic MD simulations at 27 °C from different linear combinations of the XANES spectra for the orthorhombic and cubic MD simulations at 130 °C (color-coded from yellow to red upon an increasing relative weight of the cubic MD contribution). All linear combinations yield a negative dip centered at 13.468 keV, followed by a rise around 13.480 keV and intensity modulations at higher energies. The qualitative agreement with the experiment is very satisfactory, especially the post-edge modulations starting from 13.485 keV, despite the intensity mismatch of the feature at 13.477 keV. Instead, the spectral difference of the pristine cubic minus orthorhombic XANES spectra (dotted blue) consists in two positive peaks at 13.470 and 13.483 keV and a negative band between 13.4725 and 13.480 keV, followed by smaller post-edge modulations at higher energies. The first three features of this spectrum are completely absent in the experimental difference reported in Figure 2b and are traced back to the structural changes occurring when the translational symmetry of the lattice is artificially preserved on the local scale.
Overall, the short-range XANES characterization demonstrates an increment of the sublattice disorder caused by thermal fluctuations, leading to an overall broadening of the main spectral features with temperature. This finding points to the occurrence of a symmetry reduction in the local structure of the system, in contrast with the alternative picture of thermally induced symmetry increase suggested by previous long-range characterizations. (27,28) The scenario identified with the XANES directly reflects in the XRD results presented in the following.
The T-dependent XRD I(Q) profiles measured in CsPbBr3 NCs are shown in Figure 2c. The features highlighted by the gray shaded areas correspond to superlattice peaks that arise from the periodic recurrence of cooperative octahedral tilting in the orthorhombic lattice, which doubles the unit cell constant of the ideal cubic structure along the axis perpendicular to the tilting direction, (50) as represented in Figure 1b,c. The model I(Q) profiles reported in Figure S2c show that the ideal orthorhombic unit cell is characterized by three superlattice peaks, labeled as (i), (ii), and (iii); however, in our experiment, the pronounced peak at the 1.827 Å–1 scattering vector, which comes from the background signal of the graphite sheets enclosing the sample, is superimposed to the superlattice peak (ii) and to the main reflections (022)-(202). In the range 25–120 °C, the main diffraction peaks preserve their shape and positions, whereas at 140 °C, the peak shapes change into a super-Lorentzian profile (see SI for further details). This effect points to incipient structural inhomogeneities of the sample occurring above the highest phase transition temperature, meaning that at lower temperatures the structural integrity of our sample is preserved. The disappearance of the superlattice peaks upon temperature increase up to 120 °C points to the loss of the octahedral tilting periodicity, an indication that, at this temperature, the system is in the highest temperature phase.
The XRD I(Q) profiles predicted by ab initio MD simulations are reported in Figure 2d for three different starting conditions: 27 °C and orthorhombic symmetry (gray); 130 °C and orthorhombic symmetry (yellow); 130 °C and cubic symmetry (red). The MD simulation at 27 °C confirms the presence of the three superlattice peaks (i), (ii), and (iii) and indicates that, within the lattice thermal motion, the PbBr6 octahedral tilting from which these features originate is preserved in the long-range, consistently with the orthorhombic room-temperature description of Figure 1c. Instead, the MD simulations at 130 °C lead to a strong decrease of the superlattice peaks intensity, correctly reproducing the high temperature XRD I(Q) profile of our experiment.
Even though the disappearance of the (i), (ii), and (iii) superlattice peaks was generally ascribed to an order increase of the CsPbBr3 unit cell from orthorhombic up to the cubic symmetry, (27,28) our results show that it is indeed occurring in the presence of sufficient thermal fluctuations. This effect causes the breaking of the long-range periodicity associated with the tilting of the room temperature orthorhombic structure depicted in Figure 1c, leading to a radically different conclusion from the lattice symmetry increase of Figure 1b.
Therefore, our correlative approach identifies the inorganic framework flexibility as the primary feature ruling T-induced structural changes in this perovskite system, unpacking the lattice distortions that were time-averaged in previous investigations, (23,28) thanks to the agreement between experiment and theory both in the long- and short-ranges.
Sublattice disorder in the metal halide framework was observed in organic lead and tin halide perovskites. (51) The PDF structural refinements obtained from the Fourier transform of X-ray powder diffraction showed significant internal distortions of the BX6 octahedra (with B = Pb2+, Sn2+ and X = Cl–, Br–) at short interatomic distances. The presence of time-averaged orthorhombic twin domains in the high temperature phases of inorganic lead halide perovskites NCs was identified employing Debye scattering equation analysis in a X-ray total scattering study. (23) In single crystals, thermal local fluctuations of the Pb–Br framework were experimentally shown for CsPbBr3 and MAPbBr3 in their highest temperature phase. (22) A zero-frequency Raman peak was observed, which is normally absent in purely harmonic systems, pointing to the presence of strong anharmonicity in the lead halide framework. Similar conclusions were proposed for MAPbI3 single crystals using the HERIX technique (20) and in both organic and inorganic lead iodide perovskites based on ab initio MD simulations. (52) In light of these findings, and based on our correlative structural characterization, we argue that the description of the system’s phase diagram in terms of symmetry increasing phases upon temperature rise is too simplistic. Indeed, properties such as the unusual optical band gap increase of lead halide perovskites with the temperature, which were attributed to octahedral tilting (37,53,54) in the lattice framework, can be accurately described only accounting for an increased structural disorder. (55) As such, the description of the crystal structure through its average symmetry is misleading as it leads to incorrect evaluations of crucial physical properties of the system.
Here, we rationalize our results considering the phonon anharmonicity of the inorganic perovskite framework. Phase transitions can be described by the phenomenological Landau–Ginzburg theory, which defines the temperature dependence of the free energy as a power series in an order parameter. (56) An effective microscopic description, known as soft-mode model, was proposed from neutron diffraction studies (57) for the interpretation of structural phase transitions in oxide perovskites, which are strongly anharmonic systems. In this picture, at least one phonon frequency is substantially affected by temperature changes due to anharmonic effects. This “soft” phonon mode represents the order parameter of the phase transition. Following the renormalized phonon theory, the intrinsic dependence of the soft phonon frequency from the temperature can be espressed as (58)
Figure 3
Figure 3. Theoretical predictions of the MD simulations. (a) Schematic of the excess free energy evolution with the temperature along the soft phonon coordinate of the Pb–Br–Pb octahedral tilting. The renormalized frequency of the soft phonon mode ω̃k is temperature-dependent due to its strong anharmonicity. (36) Upon temperature increase, from bottom to top, the free energy landscape along this mode changes, causing a displacive phase transition at the critical temperature Tc. (b) Probability distribution (%) of the Pb–Br–Pb angle as a function of the angle distortion: 27 °C (orthorhombic starting geometry, gray), 130 °C (orthorhombic starting geometry, orange), and 130 °C (cubic starting geometry, red). The Pb–Br–Pb angle is projected along the XZ plane, locally describing the octahedral tilting of the Pb–Br inorganic framework. The x-axis reports the difference between 180° and the Pb–Br–Pb angle projection along the XZ plane in order to center the distribution at 0°, corresponding to the ideal cubic geometry. Upon temperature increase, the Pb–Br–Pb angle probability distribution is modified, changing from bimodal to monomodal across the displacive phase transition. Inset: graphical representation of the Pb–Br–Pb angle in the plane defined by the a and c crystallographic axes (XZ plane).
In Figure 3b, the statistical distribution of the Pb–Br–Pb angle predicted by the MD simulation at 27 °C (orthorhombic starting geometry) is shown in gray. The tilting is reported as the difference between 180° and the Pb–Br–Pb angle projected along the XZ plane, such that any angular distortion with respect to the ideal cubic structure implies a deviation from the 0° value. We note that the distribution is characterized by a wide bimodal shape of the Pb–Br–Pb angle peaked at symmetric positions of ±16°. This result is consistent with the room temperature XRD I(Q) profiles reported in Figures 2c,d, characterized by the superlattice peaks arising from the periodic tilting of the PbBr6 octahedra in the system. The fit of the distribution with two identically symmetric Gaussian curves yields a standard deviation of 12° (details are reported in the SI, Figure S11).
As α is positive, a temperature increase changes the renormalized phonon frequency ω̃k2 first to zero and then to positive values, stabilizing the cubic configuration of the system since a restoring force acts on the nuclei when they are displaced from the high symmetry position. (36) Correspondingly, the minimum of the excess free energy curve is displaced as depicted in Figure 3a. This process is thus defined “displacive” phase transition, and it is driven by T-dependent anharmonic effects. In Figure 3b, our MD simulations at 130 °C (orthorhombic and cubic initial configurations, in orange and red, respectively) show the impact of the excess free energy modification on the statistical distribution of the octahedral tilting. In fact, upon temperature increase from 27 to 130 °C the Pb–Br–Pb angle distribution drastically changes, with the high temperature curves characterized by a broad monomodal distribution centered at the high symmetry position (0°) with a standard deviation of 18°. Thus, even at 130 °C, the statistical weight of strongly distorted configurations remains relevant, with extreme absolute values up to 40–60°, which are similar to those of the orthorhombic structure at 27 °C. As such, the temperature increase mainly affects the center of the distribution, i.e., the distortions of the Pb–Br–Pb bond in proximity of the ideal cubic geometry, in agreement with the predictions of a displacive phase transition. Correspondingly, the superlattice peaks in the high temperature XRD I(Q) profiles of Figure 2c,d disappear due to the loss of long-range periodicity associated with the orthorhombic tilting (Figure 1c), caused by thermal fluctuations driven by anharmonic effects.
The soft-mode model provides a microscopic description of the changes occurring in the system across the phase transition, solving the ambiguities about the presence of structural disorder in the high temperature phase of CsPbBr3. (20,22,23) The soft phonon frequency undergoes a continuous change with temperature due to the phonon anharmonicity and so does the shape of the excess free energy curve. Upon temperature increase, a discontinuity in ω̃k occurs at the phase transition temperature, defined as the temperature at which ω̃k2 changes in sign, stabilizing the average high symmetry position even though large structural distortions remain thermally accessible. At the critical temperature, other physical properties also undergo a discontinuity, such as the linear thermal expansion coefficient (59) or the ultrasonic velocity (34) for the CsPbBr3 system.
Long-range structural techniques probe the average lattice geometry of the system, which in the highest temperature phase is centered in the cubic symmetry positions. However, the thermal dynamics determine strong local distortions of the lattice, which can be observed only exploiting short-range structural characterization methods such as the XANES spectroscopy used here. Since the XANES signal originates from the statistical average of all local configurations of the probed sites, at high temperature and for this dynamic system, this observable cannot be reproduced with a unique structure having averaged lattice parameters as those obtained in PDF refinements. To our knowledge, the effect of thermal disorder on the XANES spectra was successfully reproduced only for systems in which the harmonic approximation of the phonon modes is appropriate. (47,60) Therefore, here we demonstrate that the impact of thermal dynamics on the XANES spectra can be effectively described also for largely anharmonic systems such as lead halide perovskites when ab initio MD simulations─to determine the dynamically fluctuating structures─are combined with calculations accounting for core hole final state effects to retrieve an accurate XANES line shape. Previous works characterized different sources of disorder at the local scale in the perovskite systems using PDF methods but mostly relied on a posteriori strategies in which a single time-averaged structure was considered, proposing only qualitative arguments to reconcile their inconsistency with longer range results, which agree with high symmetry structures. (23,51)
Combining both short- and long-range experimental methods with simulations, we are thus able to provide a complete description of the thermal structural changes in CsPbBr3 perovskites that is rationalized through the soft-mode model. Since this theoretical framework relies on the lattice flexibility and phonon anharmonicity of the system, we argue that the soft-mode model carries a more general validity in describing displacive thermal phase transitions in perovskites, be it oxide or lead halide and, for the latter, either inorganic or organic. Indeed, a recent T-dependent neutron scattering study reported the presence of a soft mode in MAPbBr3 single crystals, (61) with the results being likewise interpreted in terms of displacive thermal phase transitions driven by the PbBr6 octahedral tilting. Due to the common Pb–Br framework of organic and inorganic lead bromide perovskites, we can ascribe the consecutive phase transitions in CsPbBr3 to T-dependent anharmonic effects of the PbBr6 tilting mode, with the soft mode representing the order parameter of the inorganic perovskite system. The proposed scenario is also consistent with recent observations reported in ref (54).
Our analysis of the lattice thermal dynamics also helps in clarifying and quantifying the effects underlying the characteristic band gap blue shift of lead halide perovskites with the temperature rise. In the literature, it is established that both lattice expansion and octahedral tilting affect the band gap energy. (53) These structural modifications widen the band gap by decreasing the lead-halogen orbital overlap, which leads to a shift of the valence band maximum toward lower energies due to its antibonding character. Having a stronger nonbonding character, the conduction band minimum is less affected by these structural changes, resulting in a net blue shift of the band gap, which in the case of CsPbBr3 was observed to increase about 20 meV by warming up the system from room temperature up to 150 °C. (37) Over this temperature range, the lattice expansion leads to a band gap energy increase of ∼10 meV, (37) meaning that an increased octahedral tilting should account for the residual contribution. This, however, contrasts with the predictions of a symmetry increase of the average structure. Previous DFT calculations explained the blue shift of the band gap by comparing the effect of the octahedral tilting with respect to an ideal cubic structure at 0 K, leading to changes of hundreds of meV. (37,54,55) Even though these simulations show a correlation between structural deformations and band gap energies, they do not reproduce the physical process occurring upon thermal heating of the system. Our results clarify the reason why the band gap changes due to thermal structural dynamics are much smaller for temperatures above 300 K. By comparing room temperature and high temperature MD simulations, we show that thermal fluctuations lead to a reduction of the local symmetry without a significant change of the maximum amplitude of the Pb–Br–Pb tilting (Figure 3b). Since the blue shift of the band gap is related to the magnitude of the octahdral tilting, this finding explains the small influcence of the pronounced local disorder on the optical band gap of the system, with T-induced energy changes below the accuracy of DFT methods.
In conclusion, in this work we provide a consistent microscopic description of the thermal dynamics of CsPbBr3 combining short- and long-range structural sensitive techniques with ab initio MD simulations. Based on the agreement between theory and experiments, we harness our first-principles results to precisely quantify the thermal fluctuations of the system, retrieving unprecedented details on the T-dependent structural changes and their effects on the system’s properties.
The atomic-level picture emerging from the correlative characterization of CsPbBr3 is very different from the light-driven structural changes observed in CsPbBr3 NCs with time-resolved XANES: (26) upon above band gap excitation, large polarons are formed due to the electron–phonon coupling between the photocarriers and the polar inorganic lattice. The crystal distortion involves the activation of one specific longitudinal-optical phonon mode, implying well-defined nuclear displacements of the Pb–Br sublattice, which can be retrieved with atomic-scale precision by the analysis of the transient spectra. Instead, the high temperature configuration of the system is dynamically distorted and cannot be reduced, at the local scale, to an average ordered structure, thereby questioning the classical picture of a low-to-high symmetry phase transition.
These results clarify the underlying mechanisms of the lattice response under functional activation and offers strategies to control the perovskite nuclear degrees of freedom with different external stimuli. Understanding the thermal processes acting at the atomic level represents the first step toward a rational design of perovskite-based devices with improved stability.
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpclett.2c00281.
(1) Samples and characterization, (2) CsPbBr3 model crystal structures and XRD, (3) T-dependent XRD and XANES data analysis, (4) MD computational methods, (5) XANES computational methods, (6) volume expansion contribution to T-dependent XANES changes, (7) time evolution of Pb–Br–Pb angle distribution in MD simulations, (8) thermal displacements of Cs, Pb, and Br sites in MD simulations (PDF)
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Acknowledgments
This work was supported by the European Union’s Horizon 2020 research and innovation program, through the grant agreement no. 851154 (ULTRAIMAGE) and no. 695197 755 (DYNAMOX). G.F.M. acknowledges funding from Fondazione Cariplo (NanoFast 2020.2544). J.W. acknowledges funding from the Swedish Research Council (2019-03993) and the Chalmers Gender Initiative for Excellence (Genie). The computations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at NSC, C3SE, and PDC. N.C. acknowledges the support of by the SwissNSF NCCR-MARVEL. M.K. acknowledges funding by the European Union’s Horizon 2020 program, through a FET Open research and innovation action under the grant agreement no. 899141 (PoLLoC). We thank Balázs Őrley for the graphical rendering of Figure 1a.
References
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- 10Stranks, S. D.; Snaith, H. J. Metal-Halide Perovskites for Photovoltaic and Light-Emitting Devices. Nat. Nanotechnol. 2015, 10 (5), 391– 402, DOI: 10.1038/nnano.2015.90Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXnvFSqtbY%253D&md5=5911a8911c2c8cb3686acecddb114c41Metal-halide perovskites for photovoltaic and light-emitting devicesStranks, Samuel D.; Snaith, Henry J.Nature Nanotechnology (2015), 10 (5), 391-402CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)A review. Metal-halide perovskites are cryst. materials originally developed out of scientific curiosity. Unexpectedly, solar cells incorporating these perovskites are rapidly emerging as serious contenders to rival the leading photovoltaic technologies. Power conversion efficiencies have jumped from 3% to over 20% in just four years of academic research. Here, we review the rapid progress in perovskite solar cells, as well as their promising use in light-emitting devices. In particular, we describe the broad tunability and fabrication methods of these materials, the current understanding of the operation of state-of-the-art solar cells and we highlight the properties that have delivered light-emitting diodes and lasers. We discuss key thermal and operational stability challenges facing perovskites, and give an outlook of future research avenues that might bring perovskite technol. to commercialization.
- 11Smith, I. C.; Hoke, E. T.; Solis-Ibarra, D.; McGehee, M. D.; Karunadasa, H. I. A Layered Hybrid Perovskite Solar-Cell Absorber with Enhanced Moisture Stability. Angew. Chem., Int. Ed. 2014, 126 (42), 11414– 11417, DOI: 10.1002/ange.201406466Google ScholarThere is no corresponding record for this reference.
- 12Hintermayr, V. A.; Lampe, C.; Löw, M.; Roemer, J.; Vanderlinden, W.; Gramlich, M.; Böhm, A. X.; Sattler, C.; Nickel, B.; Lohmüller, T.; Urban, A. S. Polymer Nanoreactors Shield Perovskite Nanocrystals from Degradation. Nano Lett. 2019, 19 (8), 4928– 4933, DOI: 10.1021/acs.nanolett.9b00982Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsVSqtb3L&md5=61402187cb70571055da24fc7548a94ePolymer Nanoreactors Shield Perovskite Nanocrystals from DegradationHintermayr, Verena A.; Lampe, Carola; Loew, Maximilian; Roemer, Janina; Vanderlinden, Willem; Gramlich, Moritz; Boehm, Anton X.; Sattler, Cornelia; Nickel, Bert; Lohmueller, Theobald; Urban, Alexander S.Nano Letters (2019), 19 (8), 4928-4933CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Halide perovskite nanocrystals (NCs) have shown impressive advances, exhibiting optical properties that outpace conventional semiconductor NCs, such as near-unity quantum yields and ultrafast radiative decay rates. Nevertheless, the NCs suffer even more from stability problems at ambient conditions and due to moisture than their bulk counterparts. Herein, we report a strategy of employing polymer micelles as nanoreactors for the synthesis of methylammonium lead trihalide perovskite NCs. Encapsulated by this polymer shell, the NCs display strong stability against water degrdn. and halide ion migration. Thin films comprising these NCs exhibit a more than 15-fold increase in lifespan in comparison to unprotected NCs in ambient conditions and even survive over 75 days of complete immersion in water. Furthermore, the NCs, which exhibit quantum yields of up to 63% and tunability of the emission wavelength throughout the visible range, show no signs of halide ion exchange. Addnl., heterostructures of MAPI and MAPBr NC layers exhibit efficient Forster resonance energy transfer (FRET), revealing a strategy for optoelectronic integration.
- 13Pisoni, A.; Jaćimović, J.; Barišić, O. S.; Spina, M.; Gaál, R.; Forró, L.; Horváth, E. Ultra-Low Thermal Conductivity in Organic–Inorganic Hybrid Perovskite CH3NH3PbI3. J. Phys. Chem. Lett. 2014, 5 (14), 2488– 2492, DOI: 10.1021/jz5012109Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFSmsLrE&md5=5557212c144e57caf4cb172ae64e6850Ultra-Low Thermal Conductivity in Organic-Inorganic Hybrid Perovskite CH3NH3PbI3Pisoni, Andrea; Jacimovic, Jacim; Barisic, Osor S.; Spina, Massimo; Gaal, Richard; Forro, Laszlo; Horvath, EndreJournal of Physical Chemistry Letters (2014), 5 (14), 2488-2492CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The authors report on the temp. dependence of thermal cond. of single cryst. and polycryst. organometallic perovskite CH3NH3PbI3. The comparable abs. values and temp. dependence of the two samples' morphologies indicate the minor role of the grain boundaries on the heat transport. Theor. modeling demonstrates the importance of the resonant scattering in both specimens. The interaction between phonon waves and rotational degrees of freedom of CH3NH3+ sublattice emerges as the dominant mechanism for attenuation of heat transport and for ultralow thermal cond. of 0.5 W/(Km) at room temp.
- 14Mettan, X.; Pisoni, R.; Matus, P.; Pisoni, A.; Jaćimović, J.; Náfrádi, B.; Spina, M.; Pavuna, D.; Forró, L.; Horváth, E. Tuning of the Thermoelectric Figure of Merit of CH3NH3MI3 (M = Pb,Sn) Photovoltaic Perovskites. J. Phys. Chem. C 2015, 119 (21), 11506– 11510, DOI: 10.1021/acs.jpcc.5b03939Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXnsFOgu70%253D&md5=acb76244c75e00b064d6e5021eb07386Tuning of the Thermoelectric Figure of Merit of CH3NH3MI3 (M= Pb, Sn) Photovoltaic PerovskitesMettan, Xavier; Pisoni, Riccardo; Matus, Peter; Pisoni, Andrea; Jacimovic, Jacim; Nafradi, Balint; Spina, Massimo; Pavuna, Davor; Forro, Laszlo; Horvath, EndreJournal of Physical Chemistry C (2015), 119 (21), 11506-11510CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The hybrid halide perovskites, the very performant compds. in photovoltaic applications, possess large Seebeck coeff. and low thermal cond., making them potentially interesting high figure of merit (ZT) materials. For this purpose, one needs to tune the elec. cond. of these semiconductors to higher values. The authors have studied the CH3NH3MI3 (M = Pb,Sn) samples in pristine form showing very low ZT values for both materials; however, photoinduced doping (in M = Pb) and chem. doping (in M = Sn) indicate that, by further doping optimization, ZT can be enhanced toward unity and reach the performance level of the presently most efficient thermoelec. materials.
- 15Lee, W.; Li, H.; Wong, A. B.; Zhang, D.; Lai, M.; Yu, Y.; Kong, Q.; Lin, E.; Urban, J. J.; Grossman, J. C.; Yang, P. Ultralow Thermal Conductivity in All-Inorganic Halide Perovskites. Proc. Natl. Acad. Sci. U.S.A. 2017, 114 (33), 8693– 8697, DOI: 10.1073/pnas.1711744114Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1CktbfO&md5=2e6fd602d4e09513f707d3346dfb86aeUltralow thermal conductivity in all-inorganic halide perovskitesLee, Woochul; Li, Huashan; Wong, Andrew B.; Zhang, Dandan; Lai, Minliang; Yu, Yi; Kong, Qiao; Lin, Elbert; Urban, Jeffrey J.; Grossman, Jeffrey C.; Yang, PeidongProceedings of the National Academy of Sciences of the United States of America (2017), 114 (33), 8693-8697CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Controlling the flow of thermal energy is crucial to numerous applications ranging from microelectronic devices to energy storage and energy conversion devices. Here, we report ultralow lattice thermal conductivities of soln.-synthesized, single-cryst. all-inorg. halide perovskite nanowires composed of CsPbI3 (0.45 ± 0.05 W·m-1·K-1), CsPbBr3 (0.42 ± 0.04 W·m-1·K-1), and CsSnI3 (0.38 ± 0.04 W·m-1·K-1). We attribute this ultralow thermal cond. to the cluster rattling mechanism, wherein strong optical-acoustic phonon scatterings are driven by a mixt. of 0D/1D/2D collective motions. Remarkably, CsSnI3 possesses a rare combination of ultralow thermal cond., high elec. cond. (282 S·cm-1), and high hole mobility (394 cm2·V-1·s-1). The unique thermal transport properties in all-inorg. halide perovskites hold promise for diverse applications such as phononic and thermoelec. devices. Furthermore, the insights obtained from this work suggest an opportunity to discover low thermal cond. materials among unexplored inorg. crystals beyond caged and layered structures.
- 16Akkerman, Q. A.; Rainò, G.; Kovalenko, M. V.; Manna, L. Genesis, Challenges and Opportunities for Colloidal Lead Halide Perovskite Nanocrystals. Nat. Mater. 2018, 17 (5), 394– 405, DOI: 10.1038/s41563-018-0018-4Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXltFOrsrw%253D&md5=33285d81190915543b01d5ddb47c2e8bGenesis, challenges and opportunities for colloidal lead halide perovskite nanocrystalsAkkerman, Quinten A.; Raino, Gabriele; Kovalenko, Maksym V.; Manna, LiberatoNature Materials (2018), 17 (5), 394-405CODEN: NMAACR; ISSN:1476-1122. (Nature Research)A review. Lead halide perovskites (LHPs) in the form of nanometer-sized colloidal crystals, or nanocrystals (NCs), have attracted the attention of diverse materials scientists due to their unique optical versatility, high photoluminescence quantum yields and facile synthesis. LHP NCs have a 'soft' and predominantly ionic lattice, and their optical and electronic properties are highly tolerant to structural defects and surface states. Therefore, they cannot be approached with the same exptl. mindset and theor. framework as conventional semiconductor NCs. In this Review, we discuss LHP NCs historical and current research pursuits, challenges in applications, and the related present and future mitigation strategies explored.
- 17Grancini, G.; Nazeeruddin, M. K. Dimensional Tailoring of Hybrid Perovskites for Photovoltaics. Nat. Rev. Mater. 2019, 4 (1), 4– 22, DOI: 10.1038/s41578-018-0065-0Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXisFSgurrJ&md5=115a8bb52a670a6302c4c69e29deaccdDimensional tailoring of hybrid perovskites for photovoltaicsGrancini, Giulia; Nazeeruddin, Mohammad KhajaNature Reviews Materials (2019), 4 (1), 4-22CODEN: NRMADL; ISSN:2058-8437. (Nature Research)A review. Hybrid perovskites are currently one of the most active fields of research owing to their enormous potential for photovoltaics. The performance of 3D hybrid org. inorg. perovskite solar cells has increased at an incredible rate, reaching power conversion efficiencies comparable to those of many established technologies. However, the com. application of 3D hybrid perovskites is inhibited by their poor stability. Relative to 3D hybrid perovskites, low dimensional i.e., 2D hybrid perovskites have demonstrated higher moisture stability, offering new approaches to stabilizing perovskite based photovoltaic devices. Furthermore, 2D hybrid perovskites have versatile structures, enabling the fine tuning of their optoelectronic properties through compositional engineering. In this Review, we discuss the state of the art in 2D perovskites, providing an overview of structural and materials engineering aspects and optical and photophys. properties. Moreover, we discuss recent developments along with the main limitations of 3D perovskites and assess the advantages of 2D perovskites over their 3D parent structures in terms of stability. Finally, we review recent achievements in combining 3D and 2D perovskites as an approach to simultaneously boost device efficiency and stability, paving the way for mixed dimensional perovskite solar cells for com. applications.
- 18Miyata, K.; Meggiolaro, D.; Trinh, M. T.; Joshi, P. P.; Mosconi, E.; Jones, S. C.; Angelis, F. D.; Zhu, X.-Y. Large Polarons in Lead Halide Perovskites. Sci. Adv. 2017, 3 (8), e1701217 DOI: 10.1126/sciadv.1701217Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXntFGrs7s%253D&md5=817f24c41acd1772e370cc59df0c6c4cLarge polarons in lead halide perovskitesMiyata, Kiyoshi; Meggiolaro, Daniele; Trinh, M. Tuan; Joshi, Prakriti P.; Mosconi, Edoardo; Jones, Skyler C.; De Angelis, Filippo; Zhu, X.-Y.Science Advances (2017), 3 (8), e1701217/1-e1701217/9CODEN: SACDAF; ISSN:2375-2548. (American Association for the Advancement of Science)Lead halide perovskites show marked defect tolerance responsible for their excellent optoelectronic properties. These properties might be explained by the formation of large polarons, but how they are formed and whether org. cations are essential remain open questions. We provide a direct time domain view of large polaron formation in single-crystal lead bromide perovskites CH3NH3PbBr3 and CsPbBr3. We found that large polaron forms predominantly from the deformation of the PbBr3-_frameworks, irresp. of the cation type. The difference lies in the polaron formation time, which, in CH3NH3PbBr3 (0.3 ps), is less than half of that in CsPbBr3 (0.7 ps). First-principles calcns. confirm large polaron formation, identify the Pb-Br-Pb deformation modes as responsible, and explain quant. the rate difference between CH3NH3PbBr3 and CsPbBr3. The findings reveal the general advantage of the soft [PbX3]- sublattice in charge carrier protection and suggest that there is likely no mechanistic limitations in using all-inorg. or mixed-cation lead halide perovskites to overcome instability problems and to tune the balance between charge carrier protection and mobility.
- 19Miyata, K.; Atallah, T. L.; Zhu, X.-Y. Lead Halide Perovskites: Crystal-Liquid Duality, Phonon Glass Electron Crystals, and Large Polaron Formation. Sci. Adv. 2017, 3 (10), e1701469 DOI: 10.1126/sciadv.1701469Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXls1Gmtrg%253D&md5=5452e05b702672f76a2ba4e75386322aLead halide perovskites: Crystal-liquid duality, phonon glass electron crystals, and large polaron formationMiyata, Kiyoshi; Atallah, Timothy L.; Zhu, X.-Y.Science Advances (2017), 3 (10), e1701469/1-e1701469/10CODEN: SACDAF; ISSN:2375-2548. (American Association for the Advancement of Science)Lead halide perovskites have been demonstrated as high performance materials in solar cells and light-emitting devices. These materials are characterized by coherent band transport expected from cryst. semiconductors, but dielec. responses and phonon dynamics typical of liqs. This "crystal-liq." duality implies that lead halide perovskites belong to phonon glass electron crystals, a class of materials believed to make the most efficient thermoelecs.We show that the crystal-liq. duality and the resulting dielec. response are responsible for large polaron formation and screening of charge carriers, leading to defect tolerance, moderate charge carrier mobility, and radiative recombination properties. Large polaron formation, along with the phonon glass character,may also explain the marked redn. in hot carrier cooling rates in these materials.
- 20Beecher, A. N.; Semonin, O. E.; Skelton, J. M.; Frost, J. M.; Terban, M. W.; Zhai, H.; Alatas, A.; Owen, J. S.; Walsh, A.; Billinge, S. J. L. Direct Observation of Dynamic Symmetry Breaking above Room Temperature in Methylammonium Lead Iodide Perovskite. ACS Energy Lett. 2016, 1 (4), 880– 887, DOI: 10.1021/acsenergylett.6b00381Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFeku7bE&md5=9e4dae5239a4767989640330645a2f8eDirect Observation of Dynamic Symmetry Breaking above Room Temperature in Methylammonium Lead Iodide PerovskiteBeecher, Alexander N.; Semonin, Octavi E.; Skelton, Jonathan M.; Frost, Jarvist M.; Terban, Maxwell W.; Zhai, Haowei; Alatas, Ahmet; Owen, Jonathan S.; Walsh, Aron; Billinge, Simon J. L.ACS Energy Letters (2016), 1 (4), 880-887CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)Lead halide perovskites such as methylammonium lead triiodide (CH3NH3PbI3) have outstanding optical and electronic properties for photovoltaic applications, yet a full understanding of how this soln.-processable material works so well is currently missing. Previous research has revealed that CH3NH3PbI3 possesses multiple forms of static disorder regardless of prepn. method, which is surprising in light of its excellent performance. Using high energy resoln. inelastic X-ray (HERIX) scattering, we measure phonon dispersions in CH3NH3PbI3 and find direct evidence for another form of disorder in single crystals: large-amplitude anharmonic zone edge rotational instabilities of the PbI6 octahedra that persist to room temp. and above, left over from structural phase transitions that take place tens to hundreds of degrees below. Phonon calcns. show that the orientations of the methylammonium (CH3NH3+) couple strongly and cooperatively to these modes. The result is a noncentrosym., instantaneous local structure, which we observe in at. pair distribution function (PDF) measurements. This local symmetry breaking is unobservable by Bragg diffraction but can explain key material properties such as the structural phase sequence, ultralow thermal transport, and large minority charge carrier lifetimes despite moderate carrier mobility. From the PDF we est. the size of the fluctuating symmetry broken domains to be between 1 and 3 nm in diam.
- 21Cottingham, P.; Brutchey, R. L. Depressed Phase Transitions and Thermally Persistent Local Distortions in CsPbBr3 Quantum Dots. Chem. Mater. 2018, 30 (19), 6711– 6716, DOI: 10.1021/acs.chemmater.8b02295Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhs1ygtLfE&md5=2a7f6b278a8f4cc49ac46b3eaf186051Depressed Phase Transitions and Thermally Persistent Local Distortions in CsPbBr3 Quantum DotsCottingham, Patrick; Brutchey, Richard L.Chemistry of Materials (2018), 30 (19), 6711-6716CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The optoelectronic properties of CsPbX3 quantum dots (where X = Cl, Br, or I) are influenced by both their local and av. structures. Variable-temp. synchrotron X-ray diffraction measurements of CsPbBr3 quantum dots show that the temps. for both the orthorhombic-to-tetragonal (50 °C < Tγ-β < 59 °C) and tetragonal-to-cubic (108 °C < Tβ-α < 117 °C) phase transitions of the av. structure are depressed relative to their temps. in bulk CsPbBr3. Simultaneously, pair distribution function anal. of synchrotron X-ray total scattering measurements indicates that the local crystal structure of the quantum dots is best described as orthorhombically distorted over the temp. range of 22 °C < T < 160 °C, with only small changes in the magnitude of the distortion occurring during the obsd. changes in the av. structure. Taken together, these results suggest that phase transitions in CsPbBr3 quantum dots are order-disorder, involving the gradual ordering of individually coherent domains that cannot be attributed to changes in the surface area or to ferroelec. phenomena.
- 22Yaffe, O.; Guo, Y.; Tan, L. Z.; Egger, D. A.; Hull, T.; Stoumpos, C. C.; Zheng, F.; Heinz, T. F.; Kronik, L.; Kanatzidis, M. G.; Owen, J. S.; Rappe, A. M.; Pimenta, M. A.; Brus, L. E. Local Polar Fluctuations in Lead Halide Perovskite Crystals. Phys. Rev. Lett. 2017, 118 (13), 136001, DOI: 10.1103/PhysRevLett.118.136001Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFeju7zK&md5=7df46b915456003e801e23349fef1e55Local polar fluctuations in lead halide perovskite crystalsYaffe, Omer; Guo, Yinsheng; Tan, Liang Z.; Egger, David A.; Hull, Trevor; Stoumpos, Constantinos C.; Zheng, Fan; Heinz, Tony F.; Kronik, Leeor; Kanatzidis, Mercouri G.; Owen, Jonathan S.; Rappe, Andrew M.; Pimenta, Marcos A.; Brus, Louis E.Physical Review Letters (2017), 118 (13), 136001/1-136001/6CODEN: PRLTAO; ISSN:1079-7114. (American Physical Society)Hybrid lead-halide perovskites have emerged as an excellent class of photovoltaic materials. Recent reports suggest that the org. mol. cation is responsible for local polar fluctuations that inhibit carrier recombination. We combine low-frequency Raman scattering with first-principles mol. dynamics (MD) to study the fundamental nature of these local polar fluctuations. Our observations of a strong central peak in the cubic phase of both hybrid (CH3NH3PbBr3) and all-inorg. (CsPbBr3) leadhalide perovskites show that anharmonic, local polar fluctuations are intrinsic to the general lead-halide perovskite structure, and not unique to the dipolar org. cation. MD simulations indicate that head-tohead Cs motion coupled to Br face expansion, occurring on a few hundred femtosecond time scale, drives the local polar fluctuations in CsPbBr3.
- 23Bertolotti, F.; Protesescu, L.; Kovalenko, M. V.; Yakunin, S.; Cervellino, A.; Billinge, S. J. L.; Terban, M. W.; Pedersen, J. S.; Masciocchi, N.; Guagliardi, A. Coherent Nanotwins and Dynamic Disorder in Cesium Lead Halide Perovskite Nanocrystals. ACS Nano 2017, 11 (4), 3819– 3831, DOI: 10.1021/acsnano.7b00017Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlvVKjsLk%253D&md5=593da980a5192e38c74b2b79152bf3fcCoherent Nanotwins and Dynamic Disorder in Cesium Lead Halide Perovskite NanocrystalsBertolotti, Federica; Protesescu, Loredana; Kovalenko, Maksym V.; Yakunin, Sergii; Cervellino, Antonio; Billinge, Simon J. L.; Terban, Maxwell W.; Pedersen, Jan Skov; Masciocchi, Norberto; Guagliardi, AntoniettaACS Nano (2017), 11 (4), 3819-3831CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Crystal defects in highly luminescent colloidal nanocrystals (NCs) of CsPbX3 perovskites (X = Cl, Br, I) are investigated. Using X-ray total scattering techniques and the Debye scattering equation (DSE), the authors provide evidence that the local structure of these NCs always exhibits orthorhombic tilting of PbX6 octahedra within locally ordered subdomains. These subdomains are hinged through a two-/three-dimensional (2D/3D) network of twin boundaries through which the coherent arrangement of the Pb ions throughout the whole NC is preserved. The d. of these twin boundaries dets. the size of the subdomains and results in an apparent higher-symmetry structure on av. in the high-temp. modification. Dynamic cooperative rotations of PbX6 octahedra are likely at work at the twin boundaries, causing the rearrangement of the 2D or 3D network, particularly effective in the pseudocubic phases. An orthorhombic, 3D γ-phase, isostructural to that of CsPbBr3 is found here in as-synthesized CsPbI3 NCs.
- 24Gu, H.-Y.; Yin, W.-J.; Gong, X.-G. Significant Phonon Anharmonicity Drives Phase Transitions in CsPbI3. Appl. Phys. Lett. 2021, 119 (19), 191101, DOI: 10.1063/5.0072367Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXisVegs7vK&md5=a83c4c2b94add72b47c72976ebd605e7Significant phonon anharmonicity drives phase transitions in CsPbI3Gu, Hong-Yang; Yin, Wan-Jian; Gong, Xin-GaoApplied Physics Letters (2021), 119 (19), 191101CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Due to its high chem. stability and high power conversion efficiency as a solar cell absorber, the inorg. halide perovskite, CsPbI3, is considered 1 of the most promising competitors to its hybrid org.-inorg. counterpart, MeNH3PbI3. The phase transition from the photoactive black phase to the inactive yellow phase is a remarkable limitation that harms long-term phase stability. The phase transitions follow different pathways as the temp. increases and/or decreases, a phenomenon that is anomalous and remains poorly understood. The temp.-dependent free energy of CsPbI3 was systematically calcd. in different crystal phases (α, β, γ, δ) by considering the phonon contribution to the Gibbs free energy. The free energy results from calcns. that include harmonic phonons cannot reproduce exptl. observations. Alternatively, the renormalized phonon quasiparticle approach was used to derive the free energies of different CsPbI3 phases at finite temps. Based on these calcd. free energies, whose derivations included the anharmonic effect, phase-transition processes consistent with exptl. results were obsd. The anal. of the temp. effect on the phonon frequencies demonstrated that anharmonic effects in the CsPbI3 had a significant influence on its phase transitions. (c) 2021 American Institute of Physics.
- 25Lai, M.; Obliger, A.; Lu, D.; Kley, C. S.; Bischak, C. G.; Kong, Q.; Lei, T.; Dou, L.; Ginsberg, N. S.; Limmer, D. T.; Yang, P. Intrinsic Anion Diffusivity in Lead Halide Perovskites Is Facilitated by a Soft Lattice. Proc. Natl. Acad. Sci. U. S. A. 2018, 115 (47), 11929– 11934, DOI: 10.1073/pnas.1812718115Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXit1CrtrrI&md5=80e914062b1e2f581e624b7db9d7f852Intrinsic anion diffusivity in lead halide perovskites is facilitated by soft latticeLai, Minliang; Obliger, Amael; Lu, Dylan; Kley, Christopher S.; Bischak, Connor G.; Kong, Qiao; Lei, Teng; Dou, Letian; Ginsberg, Naomi S.; Limmer, David T.; Yang, PeidongProceedings of the National Academy of Sciences of the United States of America (2018), 115 (47), 11929-11934CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Facile ionic transport in lead halide perovskites plays a crit. role in device performance. Understanding the microscopic origins of high ionic conductivities has been complicated by indirect measurements and sample microstructural heterogeneities. Here, we report the direct visualization of halide anion interdiffusion in CsPbCl3, CsPbBr3 single cryst. perovskite nanowire heterojunctions using wide-field and confocal photoluminescence measurements. The combination of nanoscale imaging techniques with these single cryst. materials allows us to measure intrinsic anionic lattice diffusivities, free from complications of microscale inhomogeneity. Halide diffusivities were found to be around cm2/s at about 100° C, which are several orders of magnitudes lower than those reported in polycryst. thin films. Spatially resolved photoluminescence lifetimes and surface potential measurements provide evidence of the central role of halide vacancies in facilitating ionic diffusion. Vacancy formation free energies computed from mol. simulation are small due to the easily deformable perovskite lattice, accounting for the high equil. vacancy concn. Furthermore, mol. simulations suggest that ionic motion is facilitated by low-frequency lattice modes, resulting in low activation barriers for vacancy-mediated transport. This work elucidates the intrinsic solid-state ion diffusion mechanisms in this class of semisoft materials and offers guidelines for engineering materials with long-term stability in functional devices.
- 26Cannelli, O.; Colonna, N.; Puppin, M.; Rossi, T. C.; Kinschel, D.; Leroy, L. M. D.; Löffler, J.; Budarz, J. M.; March, A. M.; Doumy, G.; Al Haddad, A.; Tu, M.-F.; Kumagai, Y.; Walko, D.; Smolentsev, G.; Krieg, F.; Boehme, S. C.; Kovalenko, M. V.; Chergui, M.; Mancini, G. F. Quantifying Photoinduced Polaronic Distortions in Inorganic Lead Halide Perovskite Nanocrystals. J. Am. Chem. Soc. 2021, 143 (24), 9048– 9059, DOI: 10.1021/jacs.1c02403Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhtF2ktr7J&md5=79e4f2bc9941e64adb641eda25407c1aQuantifying Photoinduced Polaronic Distortions in Inorganic Lead Halide Perovskite NanocrystalsCannelli, Oliviero; Colonna, Nicola; Puppin, Michele; Rossi, Thomas C.; Kinschel, Dominik; Leroy, Ludmila M. D.; Loffler, Janina; Budarz, James M.; March, Anne Marie; Doumy, Gilles; Al Haddad, Andre; Tu, Ming-Feng; Kumagai, Yoshiaki; Walko, Donald; Smolentsev, Grigory; Krieg, Franziska; Boehme, Simon C.; Kovalenko, Maksym V.; Chergui, Majed; Mancini, Giulia F.Journal of the American Chemical Society (2021), 143 (24), 9048-9059CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The development of next-generation perovskite-based optoelectronic devices relies critically on the understanding of the interaction between charge carriers and the polar lattice in out-of-equil. conditions. While it has become increasingly evident for CsPbBr3 perovskites that the Pb-Br framework flexibility plays a key role in their light-activated functionality, the corresponding local structural rearrangement has not yet been unambiguously identified. In this work, we demonstrate that the photoinduced lattice changes in the system are due to a specific polaronic distortion, assocd. with the activation of a longitudinal optical phonon mode at 18 meV by electron-phonon coupling, and we quantify the assocd. structural changes with at.-level precision. Key to this achievement is the combination of time-resolved and temp.-dependent studies at Br K and Pb L3 X-ray absorption edges with refined ab initio simulations, which fully account for the screened core-hole final state effects on the X-ray absorption spectra. From the temporal kinetics, we show that carrier recombination reversibly unlocks the structural deformation at both Br and Pb sites. The comparison with the temp.-dependent XAS results rules out thermal effects as the primary source of distortion of the Pb-Br bonding motif during photoexcitation. Our work provides a comprehensive description of the CsPbBr3 perovskites' photophysics, offering novel insights on the light-induced response of the system and its exceptional optoelectronic properties.
- 27Hirotsu, S.; Harada, J.; Iizumi, M.; Gesi, K. Structural Phase Transitions in CsPbBr3. J. Phys. Soc. Jpn. 1974, 37 (5), 1393– 1398, DOI: 10.1143/JPSJ.37.1393Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2MXhtVWntA%253D%253D&md5=0841c7d06336c0e85933b61f74f94192Structural phase transitions in cesium tribromoplumbateHirotsu, Shunsuke; Harada, Jimpei; Iizumi, Masashi; Gesi, KazuoJournal of the Physical Society of Japan (1974), 37 (5), 1393-8CODEN: JUPSAU; ISSN:0031-9015.Structural phase transitions in perovskite-type CsPbBr3 were investigated by neutron diffraction. Phase transitions occur at 88° and 130°, which are 2nd and 1st-order, resp. The phase transition at 130° is caused by condensation of the M3 mode at the M point of the cubic Brillouin zone, while the one at 88° results from condensation of the doubly degenerate R25-like mode (Z9 mode) at the Z point of the tetragonal Brillouin zone. Group theor. considerations based on these results reveal that the crystal transforms from cubic perovskite structure (Pm3m) to tetragonal (P4/mbm) at 130° and further to orthorhombic (D162h-Pmbn) at 88°. Possible at. displacements induced at the phase transitions are obtained from the eigenvectors of the condensing modes.
- 28Stoumpos, C. C.; Malliakas, C. D.; Peters, J. A.; Liu, Z.; Sebastian, M.; Im, J.; Chasapis, T. C.; Wibowo, A. C.; Chung, D. Y.; Freeman, A. J.; Wessels, B. W.; Kanatzidis, M. G. Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation Detection. Cryst. Growth Des. 2013, 13 (7), 2722– 2727, DOI: 10.1021/cg400645tGoogle Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXosFyitLc%253D&md5=615d4e50e40aa9c8cb77e787ec333bb9Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation DetectionStoumpos, Constantinos C.; Malliakas, Christos D.; Peters, John A.; Liu, Zhifu; Sebastian, Maria; Im, Jino; Chasapis, Thomas C.; Wibowo, Arief C.; Chung, Duck Young; Freeman, Arthur J.; Wessels, Bruce W.; Kanatzidis, Mercouri G.Crystal Growth & Design (2013), 13 (7), 2722-2727CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)The synthesis, crystal growth, and structural and optoelectronic characterization was carried out for the perovskite compd. CsPbBr3. This compd. is a direct band gap semiconductor which meets most of the requirements for successful detection of X- and γ-ray radiation, such as high attenuation, high resistivity, and significant photocond. response, with detector resoln. comparable to that of com., state-of-the-art materials. A structural phase transition which occurs during crystal growth at higher temp. does not seem to affect its crystal quality. Its μτ product for both hole and electron carriers is approx. equal. The μτ product for electrons is comparable to Cd Zn telluride (CZT) and that for holes is 10 times higher than CZT.
- 29Møller, C. K. The Structure of Perovskite-like Caesium Plumbo Trihalides. Mater. Fys. Medd Danske Vidensk Selsk. 1959, 32 (2).Google ScholarThere is no corresponding record for this reference.
- 30Vanacore, G. M.; Hu, J.; Liang, W.; Bietti, S.; Sanguinetti, S.; Zewail, A. H. Diffraction of Quantum Dots Reveals Nanoscale Ultrafast Energy Localization. Nano Lett. 2014, 14 (11), 6148– 6154, DOI: 10.1021/nl502293aGoogle Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht12gur3M&md5=e89125acc39ab25a56daef9c0cd5336eDiffraction of Quantum Dots Reveals Nanoscale Ultrafast Energy LocalizationVanacore, Giovanni M.; Hu, Jianbo; Liang, Wenxi; Bietti, Sergio; Sanguinetti, Stefano; Zewail, Ahmed H.Nano Letters (2014), 14 (11), 6148-6154CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Unlike in bulk materials, energy transport in low-dimensional and nanoscale systems may be governed by a coherent ballistic behavior of lattice vibrations, the phonons. If dominant, such behavior would det. the mechanism for transport and relaxation in various energy-conversion applications. To study this coherent limit, both the spatial and temporal resolns. must be sufficient for the length-time scales involved. The lattice dynamics in nanoscale quantum dots of GaAs was obsd. using ultrafast electron diffraction. By varying the dot size h = 11-46 nm, the length scale effect was examd., together with the temporal change. When the dot size is smaller than the inelastic phonon mean-free path, the energy remains localized in high-energy acoustic modes that travel coherently within the dot. As the dot size increases, an energy dissipation toward low-energy phonons takes place, and the transport becomes diffusive. Because ultrafast diffraction provides the at.-scale resoln. and a sufficiently high time resoln., other nanostructured materials can be studied similarly to elucidate the nature of dynamical energy localization.
- 31Krieg, F.; Ochsenbein, S. T.; Yakunin, S.; ten Brinck, S.; Aellen, P.; Süess, A.; Clerc, B.; Guggisberg, D.; Nazarenko, O.; Shynkarenko, Y.; Kumar, S.; Shih, C.-J.; Infante, I.; Kovalenko, M. V. Colloidal CsPbX3 (X = Cl, Br, I) Nanocrystals 2.0: Zwitterionic Capping Ligands for Improved Durability and Stability. ACS Energy Lett. 2018, 3 (3), 641– 646, DOI: 10.1021/acsenergylett.8b00035Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXisFGrsb8%253D&md5=0f121a35e9b73499855b8799d667d8f2Colloidal CsPbX3 (X = Cl, Br, I) Nanocrystals 2.0: Zwitterionic Capping Ligands for Improved Durability and StabilityKrieg, Franziska; Ochsenbein, Stefan T.; Yakunin, Sergii; ten Brinck, Stephanie; Aellen, Philipp; Suess, Adrian; Clerc, Baptiste; Guggisberg, Dominic; Nazarenko, Olga; Shynkarenko, Yevhen; Kumar, Sudhir; Shih, Chih-Jen; Infante, Ivan; Kovalenko, Maksym V.ACS Energy Letters (2018), 3 (3), 641-646CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and optoelectronic applications are hampered by the loss of colloidal stability and structural integrity due to the facile desorption of surface capping mols. during isolation and purifn. To address this issue, herein, we propose a new ligand capping strategy utilizing common and inexpensive long-chain zwitterionic mols. such as 3-(N,N-dimethyloctadecylammonio)propanesulfonate, resulting in much improved chem. durability. In particular, this class of ligands allows for the isolation of clean NCs with high photoluminescence quantum yields (PL QYs) of above 90% after four rounds of pptn./redispersion along with much higher overall reaction yields of uniform and colloidal dispersible NCs. Densely packed films of these NCs exhibit high PL QY values and effective charge transport. Consequently, they exhibit photocond. and low thresholds for amplified spontaneous emission of 2 μJ cm-2 under femtosecond optical excitation and are suited for efficient light-emitting diodes.
- 32Guzelturk, B.; Utterback, J. K.; Coropceanu, I.; Kamysbayev, V.; Janke, E. M.; Zajac, M.; Yazdani, N.; Cotts, B. L.; Park, S.; Sood, A.; Lin, M.-F.; Reid, A. H.; Kozina, M. E.; Shen, X.; Weathersby, S. P.; Wood, V.; Salleo, A.; Wang, X.; Talapin, D. V.; Ginsberg, N. S.; Lindenberg, A. M. Nonequilibrium Thermodynamics of Colloidal Gold Nanocrystals Monitored by Ultrafast Electron Diffraction and Optical Scattering Microscopy. ACS Nano 2020, 14 (4), 4792– 4804, DOI: 10.1021/acsnano.0c00673Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXls12itLk%253D&md5=b3bf9b6e4afbebb7115212da17d2ac23Nonequilibrium Thermodynamics of Colloidal Gold Nanocrystals Monitored by Ultrafast Electron Diffraction and Optical Scattering MicroscopyGuzelturk, Burak; Utterback, James K.; Coropceanu, Igor; Kamysbayev, Vladislav; Janke, Eric M.; Zajac, Marc; Yazdani, Nuri; Cotts, Benjamin L.; Park, Suji; Sood, Aditya; Lin, Ming-Fu; Reid, Alexander H.; Kozina, Michael E.; Shen, Xiaozhe; Weathersby, Stephen P.; Wood, Vanessa; Salleo, Alberto; Wang, Xijie; Talapin, Dmitri V.; Ginsberg, Naomi S.; Lindenberg, Aaron M.ACS Nano (2020), 14 (4), 4792-4804CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Metal nanocrystals exhibit important optoelectronic and photocatalytic functionalities in response to light. These dynamic energy conversion processes have been commonly studied by transient optical probes to date, but an understanding of the atomistic response following photoexcitation has remained elusive. Here, we use femtosecond resoln. electron diffraction to investigate transient lattice responses in optically excited colloidal gold nanocrystals, revealing the effects of nanocrystal size and surface ligands on the electron-phonon coupling and thermal relaxation dynamics. First, we uncover a strong size effect on the electron-phonon coupling, which arises from reduced dielec. screening at the nanocrystal surfaces and prevails independent of the optical excitation mechanism (i.e., inter- and intraband). Second, we find that surface ligands act as a tuning parameter for hot carrier cooling. Particularly, gold nanocrystals with thiol-based ligands show significantly slower carrier cooling as compared to amine-based ligands under intraband optical excitation due to electronic coupling at the nanocrystal/ligand interfaces. Finally, we spatiotemporally resolve thermal transport and heat dissipation in photoexcited nanocrystal films by combining electron diffraction with stroboscopic elastic scattering microscopy. Taken together, we resolve the distinct thermal relaxation time scales ranging from 1 ps to 100 ns assocd. with the multiple interfaces through which heat flows at the nanoscale. Our findings provide insights into optimization of gold nanocrystals and their thin films for photocatalysis and thermoelec. applications.
- 33Mancini, G. F.; Pennacchio, F.; Latychevskaia, T.; Reguera, J.; Stellacci, F.; Carbone, F. Local Photo-Mechanical Stiffness Revealed in Gold Nanoparticles Supracrystals by Ultrafast Small-Angle Electron Diffraction. Structural Dynamics 2019, 6 (2), 024304, DOI: 10.1063/1.5091858Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXntlertbc%253D&md5=1e9813db0cd7d46b7d1c104f42fec29bLocal photo-mechanical stiffness revealed in gold nanoparticles supracrystals by ultrafast small-angle electron diffractionMancini, Giulia Fulvia; Pennacchio, Francesco; Latychevskaia, Tatiana; Reguera, Javier; Stellacci, Francesco; Carbone, FabrizioStructural Dynamics (2019), 6 (2), 024304/1-024304/6CODEN: SDTYAE; ISSN:2329-7778. (American Institute of Physics)We demonstrate that highly ordered two-dimensional crystals of ligand-capped gold nanoparticles display a local photo-mech. stiffness as high as that of solids such as graphite. In out-of-equil. electron diffraction expts., a strong temp. jump is induced in a thin film with a femtosecond laser pulse. The initial electronic excitation transfers energy to the underlying structural degrees of freedom, with a rate generally proportional to the stiffness of the material. Using femtosecond small-angle electron diffraction, we observe the temporal evolution of the diffraction feature assocd. with the nearest-neighbor nanoparticle distance. The Debye-Waller decay for the octanethiol-capped nanoparticle supracrystal, in particular, is found to be unexpectedly fast, almost as fast as the stiffest solid known and obsd. by the same technique, i.e., graphite. Our observations unravel that local stiffness in a dense supramol. assembly can be created by van der Waals interactions up to a level comparable to cryst. systems characterized by covalent bonding. (c) 2019 American Institute of Physics.
- 34Hirotsu, S.; Suzuki, T.; Sawada, S. Ultrasonic Velocity around the Successive Phase Transition Points of CsPbBr3. J. Phys. Soc. Jpn. 1977, 43 (2), 575– 582, DOI: 10.1143/JPSJ.43.575Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2sXlt1Gmt7o%253D&md5=e9dfcc1eb21a7bca21a85979a9abc172Ultrasonic velocity around the successive phase transition points of cesium lead bromide (CsPbBr3)Hirotsu, Shunsuke; Suzuki, Tomonobu; Sawada, ShozoJournal of the Physical Society of Japan (1977), 43 (2), 575-82CODEN: JUPSAU; ISSN:0031-9015.Sound velocities in perovskite-type crystal CsPbBr3 were measured around the structural phase transition points at 88 and 130°. "Detwinned" samples were used, which made it possible to relate the measured velocities to the elastic consts. in each phase. The velocities of c11 and c11-c12 modes exhibit large anomalies above and below the 2 transition points, whereas that of c44 mode is almost independent of temp. of phenomenol. and fluctuation theories. Temp. dependence of the velocity of c11 mode just above the higher transition point is consistent with the prediction from the fluctuation theory.
- 35Bechtel, J. S.; Thomas, J. C.; Van der Ven, A. Finite-Temperature Simulation of Anharmonicity and Octahedral Tilting Transitions in Halide Perovskites. Phys. Rev. Mater. 2019, 3 (11), 113605, DOI: 10.1103/PhysRevMaterials.3.113605Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhvF2ksbo%253D&md5=f9a35f5dbd4b8d3250a1e34096149d8fFinite-temperature simulation of anharmonicity and octahedral tilting transitions in halide perovskitesBechtel, Jonathon S.; Thomas, John C.; Van der Ven, AntonPhysical Review Materials (2019), 3 (11), 113605CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)Octahedral tilting transitions are obsd. in most inorg. halide perovskites and play an important role in detg. their functional and thermodn. properties. Despite existing near room temp., the cubic and tetragonal forms of halide perovskites become dynamically unstable at low temp., making it impossible to study their thermodn. properties with commonly used quasiharmonic models. An anharmonic vibrational Hamiltonian is constructed that accurately reproduces the low-energy portion of the potential-energy surface of the halide perovskite CsPbBr3. The Hamiltonian is validated using a large first-principles dataset of energies calcd. within d. functional theory for large-amplitude deformations of the CsPbBr3 crystal. Monte Carlo simulations performed on the Hamiltonian reproduce the orthorhombic-tetragonal-cubic phase transitions obsd. in CsPbBr3 and many other halide perovskites, demonstrating the importance of anharmonic vibrational excitations in stabilizing the tetragonal and cubic phases in these materials. Measures of local structure and octahedral tilting in the cubic and tetragonal phases, obtained from Monte Carlo simulations, confirm the connection between large anisotropic displacement factors and octahedral tilting, as obsd. exptl.
- 36Dove, M. T. Theory of Displacive Phase Transitions in Minerals. Am. Mineral. 1997, 82 (3–4), 213– 244, DOI: 10.2138/am-1997-3-401Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXjtFGnsr0%253D&md5=104931387037e9cc395d96b9294b1fadTheory of displacive phase transitions in mineralsDove, Martin T.American Mineralogist (1997), 82 (3-4), 213-244CODEN: AMMIAY; ISSN:0003-004X. (Mineralogical Society of America)A review with 231 refs. A lattice-dynamical treatment of displacive phase transitions leads naturally to the soft-mode model, in which the phase-transition mechanism involves a phonon frequency that falls to zero at the transition temp. The basic ideas of this approach are reviewed in relation to displacive phase transitions in silicates. A simple free-energy model is used to demonstrate that Landau theory gives a good approxn. to the free energy of the transition, provided that the entropy is primarily produced by the phonons rather than any configurational disorder. The "rigid unit mode" model provides a phys. link between the theory and the chem. bonds in silicates and this allows us to understand the origin of the transition temp. and also validates the application of the soft-mode model. The model is also used to reappraise the nature of the structures of high-temp. phases. Several issues that remain open, such as the origin of first-order phase transitions and the thermodn. of pressure-induced phase transitions, are discussed.
- 37Mannino, G.; Deretzis, I.; Smecca, E.; La Magna, A.; Alberti, A.; Ceratti, D.; Cahen, D. Temperature-Dependent Optical Band Gap in CsPbBr3, MAPbBr3, and FAPbBr3 Single Crystals. J. Phys. Chem. Lett. 2020, 11 (7), 2490– 2496, DOI: 10.1021/acs.jpclett.0c00295Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXksFajtrw%253D&md5=0eb961f1f2a411b93890b8c25e85fa5cTemperature-Dependent Optical Band Gap in CsPbBr3, MAPbBr3, and FAPbBr3 Single CrystalsMannino, Giovanni; Deretzis, Ioannis; Smecca, Emanuele; La Magna, Antonino; Alberti, Alessandra; Ceratti, Davide; Cahen, DavidJournal of Physical Chemistry Letters (2020), 11 (7), 2490-2496CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Single crystals represent a benchmark for understanding the bulk properties of halide perovskites. The dielec. functions were studied of lead bromide perovskite single crystals (MAPbBr3, CsPbBr3 and FAPbBr3) by ellipsometry at 1-5 eV while varying the temp. 183-440 K. An extremely low absorption coeff. in the sub-band gap region was found, indicating the high optical quality of all 3 crystals. The band gap values were extd. through crit. point anal. showing that Tauc-based values are systematically underestimated. The 2 structural phase transitions, i.e., orthorhombic-tetragonal and tetragonal-cubic, show distinct optical behaviors, with the former having a discontinuous character. The cross-correlation of optical data with DFT calcns. evidences the role of octahedral tilting in tailoring the value of the band gap at a given temp., whereas differences in the thermal expansion affect the slope of the band gap trend as a function of temp.
- 38Momma, K.; Izumi, F. VESTA 3 for Three-Dimensional Visualization of Crystal, Volumetric and Morphology Data. J. Appl. Crystallogr. 2011, 44 (6), 1272– 1276, DOI: 10.1107/S0021889811038970Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFSisrvP&md5=885fbd9420ed18838813d6b0166f4278VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology dataMomma, Koichi; Izumi, FujioJournal of Applied Crystallography (2011), 44 (6), 1272-1276CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)VESTA is a 3D visualization system for crystallog. studies and electronic state calcns. It was upgraded to the latest version, VESTA 3, implementing new features including drawing the external morphpol. of crysals; superimposing multiple structural models, volumetric data and crystal faces; calcn. of electron and nuclear densities from structure parameters; calcn. of Patterson functions from the structure parameters or volumetric data; integration of electron and nuclear densities by Voronoi tessellation; visualization of isosurfaces with multiple levels, detn. of the best plane for selected atoms; an extended bond-search algorithm to enable more sophisticated searches in complex mols. and cage-like structures; undo and redo is graphical user interface operations; and significant performance improvements in rendering isosurfaces and calcg. slices.
- 39VandeVondele, J.; Krack, M.; Mohamed, F.; Parrinello, M.; Chassaing, T.; Hutter, J. Quickstep: Fast and Accurate Density Functional Calculations Using a Mixed Gaussian and Plane Waves Approach. Comput. Phys. Commun. 2005, 167 (2), 103– 128, DOI: 10.1016/j.cpc.2004.12.014Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXjt1aitb4%253D&md5=8c5393031c9dbd341e0e73fcdacad486QUICKSTEP: fast and accurate density functional calculations using a mixed Gaussian and plane waves approachVandeVondele, Joost; Krack, Matthias; Mohamed, Fawzi; Parrinello, Michele; Chassaing, Thomas; Hutter, JuergComputer Physics Communications (2005), 167 (2), 103-128CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)We present the Gaussian and plane waves (GPW) method and its implementation in which is part of the freely available program package CP2K. The GPW method allows for accurate d. functional calcns. in gas and condensed phases and can be effectively used for mol. dynamics simulations. We show how derivs. of the GPW energy functional, namely ionic forces and the Kohn-Sham matrix, can be computed in a consistent way. The computational cost of computing the total energy and the Kohn-Sham matrix is scaling linearly with the system size, even for condensed phase systems of just a few tens of atoms. The efficiency of the method allows for the use of large Gaussian basis sets for systems up to 3000 atoms, and we illustrate the accuracy of the method for various basis sets in gas and condensed phases. Agreement with basis set free calcns. for single mols. and plane wave based calcns. in the condensed phase is excellent. Wave function optimization with the orbital transformation technique leads to good parallel performance, and outperforms traditional diagonalisation methods. Energy conserving Born-Oppenheimer dynamics can be performed, and a highly efficient scheme is obtained using an extrapolation of the d. matrix. We illustrate these findings with calcns. using commodity PCs as well as supercomputers.
- 40Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77 (18), 3865– 3868, DOI: 10.1103/PhysRevLett.77.3865Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmsVCgsbs%253D&md5=55943538406ee74f93aabdf882cd4630Generalized gradient approximation made simplePerdew, John P.; Burke, Kieron; Ernzerhof, MatthiasPhysical Review Letters (1996), 77 (18), 3865-3868CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Generalized gradient approxns. (GGA's) for the exchange-correlation energy improve upon the local spin d. (LSD) description of atoms, mols., and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental consts. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential.
- 41Giannozzi, P.; Baroni, S.; Bonini, N.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Chiarotti, G. L.; Cococcioni, M.; Dabo, I.; Dal Corso, A.; Gironcoli, S. de; Fabris, S.; Fratesi, G.; Gebauer, R.; Gerstmann, U.; Gougoussis, C.; Kokalj, A.; Lazzeri, M.; Martin-Samos, L.; Marzari, N.; Mauri, F.; Mazzarello, R.; Paolini, S.; Pasquarello, A.; Paulatto, L.; Sbraccia, C.; Scandolo, S.; Sclauzero, G.; Seitsonen, A. P.; Smogunov, A.; Umari, P.; Wentzcovitch, R. M. QUANTUM ESPRESSO: A Modular and Open-Source Software Project for Quantum Simulations of Materials. J. Phys.: Condens. Matter 2009, 21 (39), 395502, DOI: 10.1088/0953-8984/21/39/395502Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3Mjltl2lug%253D%253D&md5=da053fa748721b6b381051a20e7a7f53QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materialsGiannozzi Paolo; Baroni Stefano; Bonini Nicola; Calandra Matteo; Car Roberto; Cavazzoni Carlo; Ceresoli Davide; Chiarotti Guido L; Cococcioni Matteo; Dabo Ismaila; Dal Corso Andrea; de Gironcoli Stefano; Fabris Stefano; Fratesi Guido; Gebauer Ralph; Gerstmann Uwe; Gougoussis Christos; Kokalj Anton; Lazzeri Michele; Martin-Samos Layla; Marzari Nicola; Mauri Francesco; Mazzarello Riccardo; Paolini Stefano; Pasquarello Alfredo; Paulatto Lorenzo; Sbraccia Carlo; Scandolo Sandro; Sclauzero Gabriele; Seitsonen Ari P; Smogunov Alexander; Umari Paolo; Wentzcovitch Renata MJournal of physics. Condensed matter : an Institute of Physics journal (2009), 21 (39), 395502 ISSN:.QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.
- 42Giannozzi, P.; Andreussi, O.; Brumme, T.; Bunau, O.; Nardelli, M. B.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Cococcioni, M.; Colonna, N.; Carnimeo, I.; Dal Corso, A.; Gironcoli, S. de; Delugas, P.; DiStasio, R. A.; Ferretti, A.; Floris, A.; Fratesi, G.; Fugallo, G.; Gebauer, R.; Gerstmann, U.; Giustino, F.; Gorni, T.; Jia, J.; Kawamura, M.; Ko, H.-Y.; Kokalj, A.; Küçükbenli, E.; Lazzeri, M.; Marsili, M.; Marzari, N.; Mauri, F.; Nguyen, N. L.; Nguyen, H.-V.; Otero-de-la-Roza, A.; Paulatto, L.; Poncé, S.; Rocca, D.; Sabatini, R.; Santra, B.; Schlipf, M.; Seitsonen, A. P.; Smogunov, A.; Timrov, I.; Thonhauser, T.; Umari, P.; Vast, N.; Wu, X.; Baroni, S. Advanced Capabilities for Materials Modelling with Quantum ESPRESSO. J. Phys.: Condens. Matter 2017, 29 (46), 465901, DOI: 10.1088/1361-648X/aa8f79Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXntF2hsr0%253D&md5=17e46e5ac155b511f12deaeff078cc6dAdvanced capabilities for materials modelling with QUANTUM ESPRESSOGiannozzi, P.; Andreussi, O.; Brumme, T.; Bunau, O.; Buongiorno Nardelli, M.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Cococcioni, M.; Colonna, N.; Carnimeo, I.; Dal Corso, A.; de Gironcoli, S.; Delugas, P.; Di Stasio, R. A., Jr.; Ferretti, A.; Floris, A.; Fratesi, G.; Fugallo, G.; Gebauer, R.; Gerstmann, U.; Giustino, F.; Gorni, T.; Jia, J.; Kawamura, M.; Ko, H.-Y.; Kokalj, A.; Kucukbenli, E.; Lazzeri, M.; Marsili, M.; Marzari, N.; Mauri, F.; Nguyen, N. L.; Nguyen, H.-V.; Otero-de-la-Roza, A.; Paulatto, L.; Ponce, S.; Rocca, D.; Sabatini, R.; Santra, B.; Schlipf, M.; Seitsonen, A. P.; Smogunov, A.; Timrov, I.; Thonhauser, T.; Umari, P.; Vast, N.; Wu, X.; Baroni, S.Journal of Physics: Condensed Matter (2017), 29 (46), 465901/1-465901/30CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)QUANTUM ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on d.-functional theory, d.-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches. QUANTUM ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.
- 43Dal Corso, A. Pseudopotentials Periodic Table: From H to Pu. Comput. Mater. Sci. 2014, 95, 337– 350, DOI: 10.1016/j.commatsci.2014.07.043Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtlKht7vP&md5=ca160e9de8bf835c1ffee416aed3b2e2Pseudopotentials periodic table: From H to PuDal Corso, AndreaComputational Materials Science (2014), 95 (), 337-350CODEN: CMMSEM; ISSN:0927-0256. (Elsevier B.V.)We discuss the generation of a library of projector augmented-wave (PAW) and ultrasoft pseudopotentials (PPs) for all elements of the periodic table from H to Pu. The PPs are compared with two libraries: pslibrary.0.3.1 and the GBRV library (Garrity et al., 2013). The PPs are tested on the lattice consts. of the fcc and bcc structures of the 63 elements of the GBRV library. The same parameters are used to generate fully relativistic PPs that are compared with the scalar relativistic PPs. The PPs of lanthanides and actinides are tested on all-electron data available in the literature.
- 44Taillefumier, M.; Cabaret, D.; Flank, A.-M.; Mauri, F. X-Ray Absorption near-Edge Structure Calculations with the Pseudopotentials: Application to the K Edge in Diamond and α-Quartz. Phys. Rev. B 2002, 66 (19), 195107, DOI: 10.1103/PhysRevB.66.195107Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XptlKks7c%253D&md5=4a97196e36acdbc4f4c4747d1cb3dbdcX-ray absorption near-edge structure calculations with the pseudopotentials: Application to the K edge in diamond and α-quartzTaillefumier, Mathieu; Cabaret, Delphine; Flank, Anne-Marie; Mauri, FrancescoPhysical Review B: Condensed Matter and Materials Physics (2002), 66 (19), 195107/1-195107/8CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)The authors present a reciprocal-space pseudopotential scheme for calcg. x-ray absorption near-edge structure (XANES) spectra. The scheme incorporates a recursive method to compute absorption cross section as a continued fraction. The continued fraction formulation of absorption is advantageous in that it permits the treatment of core-hole interaction through large supercells (hundreds of atoms). The method is compared with recently developed Bethe-Salpeter approach. The method is applied to the C K edge in diamond and to the Si and O K edges in α-quartz for which polarized XANES spectra were measured. Core-hole effects are studied by varying the size of the supercell, thus leading to information similar to that obtained from cluster size anal. usually performed within multiple scattering calcns.
- 45Gougoussis, C.; Calandra, M.; Seitsonen, A. P.; Mauri, F. First-Principles Calculations of X-Ray Absorption in a Scheme Based on Ultrasoft Pseudopotentials: From α-Quartz to High-Tc Compounds. Phys. Rev. B 2009, 80 (7), 075102, DOI: 10.1103/PhysRevB.80.075102Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFWjsb%252FM&md5=926d9d02687ec98cf51e12f59dedd77fFirst-principles calculations of x-ray absorption in a scheme based on ultrasoft pseudopotentials: From α-quartz to high-Tc compoundsGougoussis, Christos; Calandra, Matteo; Seitsonen, Ari P.; Mauri, FrancescoPhysical Review B: Condensed Matter and Materials Physics (2009), 80 (7), 075102/1-075102/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The authors develop a 1st-principles scheme based on the continued-fraction approach and ultrasoft pseudopotentials to calc. K-edge x-ray absorption spectra in solids, allowing such calcns. in transition-metal and rare-earth compds. with substantially reduced cutoffs with respect to the norm-conserving case. The authors validate the method by calcg. Si and O K edges in α-quartz, Cu K edge in Cu and in La2CuO4. For the case of Si and O edges in α-quartz and in Cu, the authors obtain good agreement with exptl. data. In the Cu K-edge spectra of La2CuO4, a material considered a real challenge for d.-functional theory, the authors attribute all the near-edge and far-edge peaks to single-particle excitations.
- 46Prendergast, D.; Galli, G. X-Ray Absorption Spectra of Water from First Principles Calculations. Phys. Rev. Lett. 2006, 96 (21), 215502, DOI: 10.1103/PhysRevLett.96.215502Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xlt1KgtLo%253D&md5=8256bdf8d48331268d559ddcccdb2c78X-Ray Absorption Spectra of Water from First Principles CalculationsPrendergast, David; Galli, GiuliaPhysical Review Letters (2006), 96 (21), 215502/1-215502/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)We present a series of ab initio calcns. of the x-ray absorption cross section (XAS) of ice and liq. water at ambient conditions. Our results show that all available exptl. data and theor. results are consistent with the std. model of the liq. as comprising mols. with approx. four hydrogen bonds. Our simulations of ice XAS including the lowest lying excitonic state are in excellent agreement with expt. and those of a quasitetrahedral model of water are in reasonable agreement with recent measurements. Hence we propose that the std., quasitetrahedral model of water, although approx., represents a reasonably accurate description of the local structure of the liq.
- 47Nemausat, R.; Gervais, C.; Brouder, C.; Trcera, N.; Bordage, A.; Coelho-Diogo, C.; Florian, P.; Rakhmatullin, A.; Errea, I.; Paulatto, L.; Lazzeri, M.; Cabaret, D. Temperature Dependence of X-Ray Absorption and Nuclear Magnetic Resonance Spectra: Probing Quantum Vibrations of Light Elements in Oxides. Phys. Chem. Chem. Phys. 2017, 19 (8), 6246– 6256, DOI: 10.1039/C6CP08393EGoogle Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsleitbY%253D&md5=d911560ed801dc9573877f6b35b1de65Temperature dependence of X-ray absorption and nuclear magnetic resonance spectra: probing quantum vibrations of light elements in oxidesNemausat, Ruidy; Gervais, Christel; Brouder, Christian; Trcera, Nicolas; Bordage, Amelie; Coelho-Diogo, Cristina; Florian, Pierre; Rakhmatullin, Aydar; Errea, Ion; Paulatto, Lorenzo; Lazzeri, Michele; Cabaret, DelphinePhysical Chemistry Chemical Physics (2017), 19 (8), 6246-6256CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)A combined exptl.-theor. study on the temp. dependence of the x-ray absorption near-edge structure (XANES) and NMR spectra of periclase (MgO), spinel (MgAl2O4), corundum (α-Al2O3), berlinite (α-AlPO4), stishovite and α-quartz (SiO2) is reported. Predictive calcns. are presented when exptl. data are not available. For these light-element oxides, both exptl. techniques detect systematic effects related to quantum thermal vibrations which are well reproduced by d.-functional theory simulations. In calcns., thermal fluctuations of the nuclei are included by considering nonequil. configurations according to finite-temp. quantum statistics at the quasiharmonic level. The influence of nuclear quantum fluctuations on XANES and NMR spectroscopies is particularly sensitive to the coordination no. of the probed cation. Also, the relative importance of nuclear dynamics and thermal expansion is quantified over a large range of temps.
- 48Rehr, J. J.; Albers, R. C. Theoretical Approaches to X-Ray Absorption Fine Structure. Rev. Mod. Phys. 2000, 72 (3), 621– 654, DOI: 10.1103/RevModPhys.72.621Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXmtVOqtrg%253D&md5=5fb478a8ff6028b7ba5681921050fca7Theoretical approaches to x-ray absorption fine structureRehr, J. J.; Albers, R. C.Reviews of Modern Physics (2000), 72 (3), 621-654CODEN: RMPHAT; ISSN:0034-6861. (American Physical Society)Dramatic advances in the understanding of x-ray absorption fine structure (XAFS) were made over the past few decades, which led ultimately to a highly quant. theory. This review with many refs. covers these developments from a unified multiple-scattering viewpoint. The authors focus on extended x-ray absorption fine structure (EXAFS) well above an x-ray edge, and, to a lesser extent, on x-ray absorption near-edge structure (XANES) closer to an edge. The discussion includes both formal considerations, derived from a many-electron formulation, and practical computational methods based on independent-electron models, with many-body effects lumped into various inelastic losses and energy shifts. The main conceptual issues in XAFS theory are identified and their relative importance is assessed; these include the convergence of the multiple-scattering expansion, curved-wave effects, the scattering potential, inelastic losses, self-energy shifts, and vibrations and structural disorder. The advantages and limitations of current computational approaches are addressed, with particular regard to quant. exptl. comparisons.
- 49Teo, B. K. EXAFS: Basic Principles and Data Analysis; Springer Science & Business Media, 2012.Google ScholarThere is no corresponding record for this reference.
- 50Glazer, A. M. Simple Ways of Determining Perovskite Structures. Acta Crystallogr., Sect. A: Found. Crystallogr. 1975, 31 (6), 756– 762, DOI: 10.1107/S0567739475001635Google ScholarThere is no corresponding record for this reference.
- 51Worhatch, R. J.; Kim, H.; Swainson, I. P.; Yonkeu, A. L.; Billinge, S. J. L. Study of Local Structure in Selected Organic–Inorganic Perovskites in the Pm3̅m Phase. Chem. Mater. 2008, 20 (4), 1272– 1277, DOI: 10.1021/cm702668dGoogle Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXps1Krsw%253D%253D&md5=83b85b82b8d8a8d1edbc51320f8a074fStudy of Local Structure in Selected Organic-Inorganic Perovskites in the Pm‾3m PhaseWorhatch, Richard J.; Kim, HyunJeong; Swainson, Ian P.; Yonkeu, Andre L.; Billinge, Simon J. L.Chemistry of Materials (2008), 20 (4), 1272-1277CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The local structures of the inorg. component of selected org.-inorg. perovskites (OIPs) were studied by analyzing the x-ray pair distribution function. Whereas the long-range structure of each perovskite is the untilted Pm3‾m phase, all the OIPs showed significant internal distortion of the octahedra. Varying the halide has a significant impact on the lattice const. There is evidence of local lone-pair distortions for certain compns. The most complex case of disorder appears to be that of CH3NH3SnBr3.
- 52Carignano, M. A.; Aravindh, S. A.; Roqan, I. S.; Even, J.; Katan, C. Critical Fluctuations and Anharmonicity in Lead Iodide Perovskites from Molecular Dynamics Supercell Simulations. J. Phys. Chem. C 2017, 121 (38), 20729– 20738, DOI: 10.1021/acs.jpcc.7b08220Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVeksrbJ&md5=2e6d110e2e834828571e32954a4354ecCritical Fluctuations and Anharmonicity in Lead Iodide Perovskites from Molecular Dynamics Supercell SimulationsCarignano, Marcelo A.; Aravindh, S. Assa; Roqan, Iman S.; Even, Jacky; Katan, ClaudineJournal of Physical Chemistry C (2017), 121 (38), 20729-20738CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The authors present a systematic study based on 1st-principles mol. dynamics simulations of lead iodide perovskites with 3 different cations, including methylammonium (MA), formamidinium (FA), and Cs. Using the high-temp. perovskite structure as a ref., the authors study the instabilities that develop as the material is cooled down to 370 K. All 3 perovskites display anharmonicity in the motion of the I atoms, with the stronger effect obsd. for the MAPbI3 and CsPbI3. At high temp., this behavior can be traced back to the reduced effective size of the Cs+ and MA+ cations. MAPbI3 undergoes a spontaneous phase transition within the simulation model driven by the dipolar interaction between neighboring MA cations as the temp. is decreased from 450 K. The reverse transformation from tetragonal to cubic is also monitored through the large distribution of the octahedral tilting angles accompanied by an increase in the anharmonicity of the I atom motion. Both MA and FA hybrid perovskites show a strong coupling between the mol. orientations and the local lattice deformations, suggesting mixed order-disorder/displacive characters of the high-temp. phase transitions.
- 53Prasanna, R.; Gold-Parker, A.; Leijtens, T.; Conings, B.; Babayigit, A.; Boyen, H.-G.; Toney, M. F.; McGehee, M. D. Band Gap Tuning via Lattice Contraction and Octahedral Tilting in Perovskite Materials for Photovoltaics. J. Am. Chem. Soc. 2017, 139 (32), 11117– 11124, DOI: 10.1021/jacs.7b04981Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFKkurrM&md5=849c6ff83b9086c4abc02ee59256fb21Band Gap Tuning via Lattice Contraction and Octahedral Tilting in Perovskite Materials for PhotovoltaicsPrasanna, Rohit; Gold-Parker, Aryeh; Leijtens, Tomas; Conings, Bert; Babayigit, Aslihan; Boyen, Hans-Gerd; Toney, Michael F.; McGehee, Michael D.Journal of the American Chemical Society (2017), 139 (32), 11117-11124CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Tin and lead iodide perovskite semiconductors of the compn. AMX3, where M is a metal and X is a halide, are leading candidates for high efficiency low cost tandem photovoltaics, in part because they have band gaps that can be tuned over a wide range by compositional substitution. We exptl. identify two competing mechanisms through which the A-site cation influences the band gap of 3D metal halide perovskites. Using a smaller A-site cation can distort the perovskite lattice in two distinct ways: by tilting the MX6 octahedra or by simply contracting the lattice isotropically. The former effect tends to raise the band gap, while the latter tends to decrease it. Lead iodide perovskites show an increase in band gap upon partial substitution of the larger formamidinium with the smaller cesium, due to octahedral tilting. Perovskites based on tin, which is slightly smaller than lead, show the opposite trend: they show no octahedral tilting upon Cs-substitution but only a contraction of the lattice, leading to progressive redn. of the band gap. We outline a strategy to systematically tune the band gap and valence and conduction band positions of metal halide perovskites through control of the cation compn. Using this strategy, we demonstrate solar cells that harvest light in the IR up to 1040 nm, reaching a stabilized power conversion efficiency of 17.8%, showing promise for improvements of the bottom cell of all-perovskite tandem solar cells. The mechanisms of cation-based band gap tuning we describe are broadly applicable to 3D metal halide perovskites and will be useful in further development of perovskite semiconductors for optoelectronic applications.
- 54Lanigan-Atkins, T.; He, X.; Krogstad, M. J.; Pajerowski, D. M.; Abernathy, D. L.; Xu, G. N. M. N.; Xu, Z.; Chung, D.-Y.; Kanatzidis, M. G.; Rosenkranz, S.; Osborn, R.; Delaire, O. Two-Dimensional Overdamped Fluctuations of the Soft Perovskite Lattice in CsPbBr3. Nat. Mater. 2021, 20 (7), 977– 983, DOI: 10.1038/s41563-021-00947-yGoogle Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXmsF2ju7c%253D&md5=a57c2279298f7fedbfc0bee62602ce89Two-dimensional overdamped fluctuations of the soft perovskite lattice in CsPbBr3Lanigan-Atkins, T.; He, X.; Krogstad, M. J.; Pajerowski, D. M.; Abernathy, D. L.; Xu, Guangyong N. M. N.; Xu, Zhijun; Chung, D.-Y.; Kanatzidis, M. G.; Rosenkranz, S.; Osborn, R.; Delaire, O.Nature Materials (2021), 20 (7), 977-983CODEN: NMAACR; ISSN:1476-1122. (Nature Portfolio)Lead halide perovskites exhibit structural instabilities and large at. fluctuations thought to impact their optical and thermal properties, yet detailed structural and temporal correlations of their at. motions remain poorly understood. Here, these correlations are resolved in CsPbBr3 crystals using momentum-resolved neutron and X-ray scattering measurements as a function of temp., complemented with first-principles simulations. We uncover a striking network of diffuse scattering rods, arising from the liq.-like damping of low-energy Br-dominated phonons, reproduced in our simulations of the anharmonic phonon self-energy. These overdamped modes cover a continuum of wave vectors along the edges of the cubic Brillouin zone, corresponding to two-dimensional sheets of correlated rotations in real space, and could represent precursors to proposed two-dimensional polarons. Further, these motions directly impact the electronic gap edge states, linking soft anharmonic lattice dynamics and optoelectronic properties. These results provide insights into the highly unusual at. dynamics of halide perovskites, relevant to further optimization of their optical and thermal properties.
- 55Wiktor, J.; Rothlisberger, U.; Pasquarello, A. Predictive Determination of Band Gaps of Inorganic Halide Perovskites. J. Phys. Chem. Lett. 2017, 8 (22), 5507– 5512, DOI: 10.1021/acs.jpclett.7b02648Google Scholar55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslags7%252FO&md5=512e8efb5884cde66ed5919664952eadPredictive Determination of Band Gaps of Inorganic Halide PerovskitesWiktor, Julia; Rothlisberger, Ursula; Pasquarello, AlfredoJournal of Physical Chemistry Letters (2017), 8 (22), 5507-5512CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)We carry out first-principles calcns. of band gaps of cubic inorg. perovskites belonging to the class CsBX3, with B = Pb, Sn and X = Cl, Br, I. We use the quasi-particle self-consistent GW method with efficient vertex corrections to calc. the electronic structure of the studied materials. We demonstrate the importance of including the higher-lying core and semicore shells among the valence states. For a meaningful comparison with exptl. values, we account for thermal vibrations and disorder through ab initio mol. dynamics. Addnl., we calc. the spin-orbit coupling at levels of theory of increasing accuracy and show that semilocal d. functionals significantly underestimate these corrections. We show that all of these effects need to be properly included in order to obtain reliable predictions for the band gaps of halide perovskites.
- 56Bruce, A. D.; Cowley, R. A. Structural Phase Transitions; Monographs on physics; Taylor & Francis: London, 1981.Google ScholarThere is no corresponding record for this reference.
- 57Shirane, G. Neutron Scattering Studies of Structural Phase Transitions at Brookhaven. Rev. Mod. Phys. 1974, 46 (3), 437– 449, DOI: 10.1103/RevModPhys.46.437Google Scholar57https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2cXlt1Olsbo%253D&md5=6a8670e726292af013cdba3ec5111e96Neutron scattering studies of structural phase transitions at BrookhavenShirane, G.Reviews of Modern Physics (1974), 46 (3), 437-49CODEN: RMPHAT; ISSN:0034-6861.A review of systematic neturon scattering studies on phase transitions carried out at Brookhaven is given with 57 refs.
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- 59Rodová, M.; Brožek, J.; Knížek, K.; Nitsch, K. Phase Transitions in Ternary Caesium Lead Bromide. J. Therm. Anal. Calorim. 2003, 71 (2), 667– 673, DOI: 10.1023/A:1022836800820Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXitVynsbs%253D&md5=1f443a54159b2217749ed085191a2796Phase transitions in ternary cesium lead bromideRodova, M.; Brozek, J.; Knizek, K.; Nitsch, K.Journal of Thermal Analysis and Calorimetry (2003), 71 (2), 667-673CODEN: JTACF7; ISSN:1388-6150. (Kluwer Academic Publishers)Phase transitions in CsPbBr3 were studied by DSC, TMA and high temp. x-ray diffraction. The samples were prepd. from soln. by H2O evapn. and from the melt. On the DSC curves as well as on the temp. dependence of the lattice consts. of CsPbBr3 only two effects were found belonging to the earlier published phase transitions at 88 and 130° and no further effects. Linear thermal expansion coeffs. α of individual CsPbBr3 modifications were calcd. from both TMA and high temp. x-ray diffraction. The structural parameters of the room temp. orthorhombic phase were refined. CsPbBr3 prepd. from the soln. contained ∼10% of CsPb2Br5 and so the DSC curve of pure CsPb2Br5 was also measured and an effect at a temp. of 68.5° was found.
- 60Nemausat, R.; Cabaret, D.; Gervais, C.; Brouder, C.; Trcera, N.; Bordage, A.; Errea, I.; Mauri, F. Phonon Effects on X-Ray Absorption and Nuclear Magnetic Resonance Spectroscopies. Phys. Rev. B 2015, 92 (14), 144310, DOI: 10.1103/PhysRevB.92.144310Google Scholar60https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktVKjsLc%253D&md5=8febac528fd70e67a5ff8bef51da3471Phonon effects on X-ray absorption and nuclear magnetic resonance spectroscopiesNemausat, Ruidy; Cabaret, Delphine; Gervais, Christel; Brouder, Christian; Trcera, Nicolas; Bordage, Amelie; Errea, Ion; Mauri, FrancescoPhysical Review B: Condensed Matter and Materials Physics (2015), 92 (14), 144310/1-144310/12CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)In material sciences, spectroscopic approaches combining ab initio calcns. with expts. are commonly used to accurately analyze the exptl. spectral data. Most state-of-the-art first-principles calcns. are usually performed assuming an equil. static lattice. Yet, nuclear motion affects spectra even when reduced to the zero-point motion at 0 K. We propose a framework based on d.-functional theory that includes quantum thermal fluctuations in theor. x-ray absorption near-edge structure (XANES) and solid-state NMR (NMR) spectroscopies and allows to well describe temp. effects obsd. exptl. Within the Born-Oppenheimer and quasiharmonic approxns., we incorporate the nuclear motion by generating several nonequil. configurations from the dynamical matrix. The averaged calcd. XANES and NMR spectral data have been compared to expts. in MgO. The good agreement obtained between expts. and calcns. validates the developed approach, which suggests that calcg. the XANES spectra at finite temp. by averaging individual nonequil. configurations is a suitable approxn. This study highlights the relevance of phonon renormalization and the relative contributions of thermal expansion and nuclear dynamics on NMR and XANES spectra on a wide range of temps.
- 61Swainson, I. P.; Stock, C.; Parker, S. F.; Van Eijck, L.; Russina, M.; Taylor, J. W. From Soft Harmonic Phonons to Fast Relaxational Dynamics in CH3NH3PbBr3. Phys. Rev. B 2015, 92 (10), 100303, DOI: 10.1103/PhysRevB.92.100303Google Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjtVyhsL8%253D&md5=1be5add9e7055f0b2a3e9337e0038d40From soft harmonic phonons to fast relaxational dynamics in CH3NH3PbBr3Swainson, I. P.; Stock, C.; Parker, S. F.; Van Eijck, L.; Russina, M.; Taylor, J. W.Physical Review B: Condensed Matter and Materials Physics (2015), 92 (10), 100303/1-100303/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The lead-halide perovskites, including CH3NH3PbBr3, are components in cost effective, highly efficient photovoltaics, where the interactions of the mol. cations with the inorg. framework are suggested to influence the electronic and ferroelec. properties. CH3NH3PbBr3 undergoes a series of structural transitions assocd. with orientational order of the CH3NH3 (methylammonium) mol. cation and tilting of the PbBr3 host framework. We apply high-resoln. neutron scattering to study the soft harmonic phonons assocd. with these transitions, and find a strong coupling between the PbBr3 framework and the quasistatic CH3NH3 dynamics at low energy transfers. At higher energy transfers, we observe a PbBr6 octahedra soft mode driving a transition at 150 K from bound mol. excitations at low temps. to relatively fast relaxational excitations that extend up to ∼50-100 meV. We suggest that these temporally overdamped dynamics enables possible indirect band gap processes in these materials that are related to the enhanced photovoltaic properties.
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Abstract
Figure 1
Figure 1. (a) Multiscale probing of thermally induced changes in CsPbBr3 perovskite nanocrystals: schematic layout of the experiment. T-dependent XRD and XANES measurements were conducted in parallel on CsPbBr3 dry nanocrystals, respectively at 12.9 keV and at the Br K-edge (13.450–13.570 keV). Courtesy of Balázs Őrley. CsPbBr3 crystal structures: (b) Pm3̅m cubic and (c) Pnma orthorhombic unit cell graphics, each with a schematic for the tilting of the inorganic framework. In the orthorhombic phase, the ordered tilting of the PbBr6 octahedra causes the doubling of the unit cell constant along the crystallographic c-axis. (50)
Figure 2
Figure 2. Correlative short- and long-range T-dependent structural characterization of CsPbBr3. (a) Experimental Br K-edge XANES spectra of CsPbBr3 NCs at 25 °C (dashed gray) and at 120 °C (dashed red), ab initio XANES spectra for the pristine orthorhombic and cubic structures obtained from a PDF refinement of XRD data (21) (dotted blue and dotted red, respectively), and ab initio XANES spectra for the MD simulations at 27 °C (orthorhombic starting symmetry, gray) and 130 °C (orthorhombic and cubic starting symmetries, yellow and red, respectively). All spectra were scaled by their underlying areas and vertically offset. (b) Br K-edge XANES differences for 120 °C minus 25 °C (experiment, dashed gray), pristine cubic minus pristine orthorhombic from PDF refinements (dotted blue) and the difference between the linear combinations of cubic 130 °C and orthorhombic 130 °C minus orthorhombic 27 °C MD simulations. The curves were obtained considering different coefficients of the cubic 130 °C and orthorhombic 130 °C MD spectra, from 100% cubic (red) to 100% orthorhombic (yellow). A 3-point adjacent averaging of the energy axis was performed for the experimental thermal difference, whereas the simulated spectral differences were multiplied by a factor ×0.30 (MD) and ×0.15 (pristine), the latter also being vertically shifted, to enable a straightforward comparison with the experiment. (c) Experimental XRD I(Q) profiles of CsPbBr3 NCs as a function of the temperature from 25 to 140 °C. The sharp feature at 1.827 Å–1 originates from the graphite peak enclosing the sample (blue curve). The shaded gray areas mark the region of the (i) and (iii) superlattice peaks, which disappear upon temperature increase. (d) XRD I(Q) profiles predicted from the MD simulations at 27 °C with orthorhombic starting geometry (gray), 130 °C with orthorhombic starting geometry (yellow) and 130 °C with cubic starting geometry (red). The shaded gray areas highlight the (i), (ii), and (iii) superlattice peaks. Inset: zoom into the 1.55–1.94 Å–1 region of the superlattice peaks. In the legend of each panel, “ortho” stands for “orthorhombic”.
Figure 3
Figure 3. Theoretical predictions of the MD simulations. (a) Schematic of the excess free energy evolution with the temperature along the soft phonon coordinate of the Pb–Br–Pb octahedral tilting. The renormalized frequency of the soft phonon mode ω̃k is temperature-dependent due to its strong anharmonicity. (36) Upon temperature increase, from bottom to top, the free energy landscape along this mode changes, causing a displacive phase transition at the critical temperature Tc. (b) Probability distribution (%) of the Pb–Br–Pb angle as a function of the angle distortion: 27 °C (orthorhombic starting geometry, gray), 130 °C (orthorhombic starting geometry, orange), and 130 °C (cubic starting geometry, red). The Pb–Br–Pb angle is projected along the XZ plane, locally describing the octahedral tilting of the Pb–Br inorganic framework. The x-axis reports the difference between 180° and the Pb–Br–Pb angle projection along the XZ plane in order to center the distribution at 0°, corresponding to the ideal cubic geometry. Upon temperature increase, the Pb–Br–Pb angle probability distribution is modified, changing from bimodal to monomodal across the displacive phase transition. Inset: graphical representation of the Pb–Br–Pb angle in the plane defined by the a and c crystallographic axes (XZ plane).
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- 1Berhe, T. A.; Su, W.-N.; Chen, C.-H.; Pan, C.-J.; Cheng, J.-H.; Chen, H.-M.; Tsai, M.-C.; Chen, L.-Y.; Aregahegn Dubale, A.; Hwang, B.-J. Organometal Halide Perovskite Solar Cells: Degradation and Stability. Energy Environ. Sci. 2016, 9 (2), 323– 356, DOI: 10.1039/C5EE02733K1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs1yjtL7L&md5=3097ce160d6e8b1d57560ecae5e271b9Organometal halide perovskite solar cells: degradation and stabilityBerhe, Taame Abraha; Su, Wei-Nien; Chen, Ching-Hsiang; Pan, Chun-Jern; Cheng, Ju-Hsiang; Chen, Hung-Ming; Tsai, Meng-Che; Chen, Liang-Yih; Dubale, Amare Aregahegn; Hwang, Bing-JoeEnergy & Environmental Science (2016), 9 (2), 323-356CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)Organometal halide perovskite solar cells have evolved in an exponential manner in the two key areas of efficiency and stability. The power conversion efficiency (PCE) reached 20.1% late last year. The key disquiet was stability, which has been limiting practical application, but now the state of the art is promising, being measured in thousands of hours. These improvements have been achieved through the application of different materials, interfaces and device architecture optimizations, esp. after the investigation of hole conductor free mesoporous devices incorporating carbon electrodes, which promise stable, low cost and easy device fabrication methods. However, this work is still far from complete. There are various issues assocd. with the degrdn. of Omh-perovskite, and the interface and device instability which must be addressed to achieve good reproducibility and long lifetimes for Omh-PSCs with high conversion efficiencies. A comprehensive understanding of these issues is required to achieve breakthroughs in stability and practical outdoor applications of Omh-PSCs. For successful small and large scale applications, besides the improvement of the PCE, the stability of Omh-PSCs has to be improved. The causes of failure and assocd. mechanisms of device degrdn., followed by the origins of degrdn., approaches to improve stability, and methods and protocols are discussed in detail and form the main focus of this review article.
- 2Correa-Baena, J.-P.; Saliba, M.; Buonassisi, T.; Grätzel, M.; Abate, A.; Tress, W.; Hagfeldt, A. Promises and Challenges of Perovskite Solar Cells. Science 2017, 358 (6364), 739– 744, DOI: 10.1126/science.aam63232https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslOnsLzO&md5=5f8fc7efbe8fa550c7b71e312ba7100aPromises and challenges of perovskite solar cellsCorrea-Baena, Juan-Pablo; Saliba, Michael; Buonassisi, Tonio; Graetzel, Michael; Abate, Antonio; Tress, Wolfgang; Hagfeldt, AndersScience (Washington, DC, United States) (2017), 358 (6364), 739-744CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)A review is given. The efficiencies of perovskite solar cells have gone from single digits to a certified 22.1% in a few years' time. At this stage of their development, the key issues concern how to achieve further improvements in efficiency and long-term stability. We review recent developments in the quest to improve the current state of the art. Because photocurrents are near the theor. max., our focus is on efforts to increase open-circuit voltage by improving charge-selective contacts and charge carrier lifetimes in perovskites via processes such as ion tailoring. The challenges assocd. with long-term perovskite solar cell device stability include the role of testing protocols, ionic movement affecting performance metrics over extended periods of time, and detn. of the best ways to counteract degrdn. mechanisms.
- 3Nayak, P. K.; Mahesh, S.; Snaith, H. J.; Cahen, D. Photovoltaic Solar Cell Technologies: Analysing the State of the Art. Nat. Rev. Mater. 2019, 4 (4), 269– 285, DOI: 10.1038/s41578-019-0097-03https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXptFyrsb0%253D&md5=c20b519380f3ac55218b7d7abe84ba8ePhotovoltaic solar cell technologiesNayak, Pabitra K.; Mahesh, Suhas; Snaith, Henry J.; Cahen, DavidNature Reviews Materials (2019), 4 (4), 269-285CODEN: NRMADL; ISSN:2058-8437. (Nature Research)The remarkable development in photovoltaic (PV) technologies over the past 5 years calls for a renewed assessment of their performance and potential for future progress. Here, we analyze the progress in cells and modules based on single-cryst. GaAs, Si, GaInP and InP, multicryst. Si as well as thin films of polycryst. CdTe and CuInxGa1-xSe2. In addn., we analyze the PV developments of the more recently emerged lead halide perovskites together with notable improvements in sustainable chalcogenides, org. PVs and quantum dots technologies. In addn. to power conversion efficiencies, we consider many of the factors that affect power output for each cell type and note improvements in control over the optoelectronic quality of PV-relevant materials and interfaces and the discovery of new material properties. By comparing PV cell parameters across technologies, we appraise how far each technol. may progress in the near future. Although accurate or revolutionary developments cannot be predicted, cross-fertilization between technologies often occurs, making achievements in one cell type an indicator of evolutionary developments in others. This knowledge transfer is timely, as the development of metal halide perovskites is helping to unite previously disparate, technol.-focused strands of PV research.
- 4Liu, X.-K.; Xu, W.; Bai, S.; Jin, Y.; Wang, J.; Friend, R. H.; Gao, F. Metal Halide Perovskites for Light-Emitting Diodes. Nat. Mater. 2021, 20, 10– 21, DOI: 10.1038/s41563-020-0784-74https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhvVCltLvN&md5=62903a8b6c6d24628adff59e93ab1721Metal halide perovskites for light-emitting diodesLiu, Xiao-Ke; Xu, Weidong; Bai, Sai; Jin, Yizheng; Wang, Jianpu; Friend, Richard H.; Gao, FengNature Materials (2021), 20 (1), 10-21CODEN: NMAACR; ISSN:1476-1122. (Nature Research)A review. Metal halide perovskites have shown promising optoelectronic properties suitable for light-emitting applications. The development of perovskite light-emitting diodes (PeLEDs) has progressed rapidly over the past several years, reaching high external quantum efficiencies of over 20%. In this Review, we focus on the key requirements for high-performance PeLEDs, highlight recent advances on materials and devices, and emphasize the importance of reliable characterization of PeLEDs. We discuss possible approaches to improve the performance of blue and red PeLEDs, increase the long-term operational stability and reduce toxicity hazards. We also provide an overview of the application space made possible by recent developments in high-efficiency PeLEDs.
- 5Leijtens, T.; Eperon, G. E.; Pathak, S.; Abate, A.; Lee, M. M.; Snaith, H. J. Overcoming Ultraviolet Light Instability of Sensitized TiO2 with Meso-Superstructured Organometal Tri-Halide Perovskite Solar Cells. Nat. Commun. 2013, 4 (1), 2885, DOI: 10.1038/ncomms38855https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2c3jtFCmsg%253D%253D&md5=f35cffa6aec16d6b018913b9ddfa9608Overcoming ultraviolet light instability of sensitized TiO2 with meso-superstructured organometal tri-halide perovskite solar cellsLeijtens Tomas; Eperon Giles E; Pathak Sandeep; Abate Antonio; Lee Michael M; Snaith Henry JNature communications (2013), 4 (), 2885 ISSN:.The power conversion efficiency of hybrid solid-state solar cells has more than doubled from 7 to 15% over the past year. This is largely as a result of the incorporation of organometallic trihalide perovskite absorbers into these devices. But, as promising as this development is, long-term operational stability is just as important as initial conversion efficiency when it comes to the development of practical solid-state solar cells. Here we identify a critical instability in mesoporous TiO2-sensitized solar cells arising from light-induced desorption of surface-adsorbed oxygen. We show that this instability does not arise in mesoporous TiO2-free mesosuperstructured solar cells. Moreover, our TiO2-free cells deliver stable photocurrent for over 1,000 h continuous exposure and operation under full spectrum simulated sunlight.
- 6Wang, D.; Wright, M.; Elumalai, N. K.; Uddin, A. Stability of Perovskite Solar Cells. Sol. Energy Mater. Sol. Cells 2016, 147, 255– 275, DOI: 10.1016/j.solmat.2015.12.0256https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlygtQ%253D%253D&md5=bbeb0a2e8c23923fcd88960e5a92dd92Stability of perovskite solar cellsWang, Dian; Wright, Matthew; Elumalai, Naveen Kumar; Uddin, AshrafSolar Energy Materials & Solar Cells (2016), 147 (), 255-275CODEN: SEMCEQ; ISSN:0927-0248. (Elsevier B.V.)The performance of perovskite solar cells has increased at an unprecedented rate, with efficiencies currently exceeding 20%. This technol. is particularly promising, as it is compatible with cheap soln. processing. For a thin-film solar product to be com. viable, it must pass the IEC 61646 testing stds., regarding the environmental stability. Currently, the poor stability of perovskite solar cells is a barrier to commercialization. The main issue causing this problem is the instability of the perovskite layer when in contact with moisture; however, it is important to explore stability problems with the other layers and interfaces within the device. The stability issues discussed in this review highlight the need to view the device as a whole system, due to the interdependent relationships between the layers, including: the perovskite absorber, electron transport layers, hole transport layers, other buffer layers and the electrodes. We also discuss other issues pertaining to device stability, such as measurement-induced hysteresis and the requirement for std. testing protocols. For perovskite solar cells to achieve the required stability, future research must focus on improving the intrinsic stability of the perovskite absorber layer, carefully designing the device geometry, and finding durable encapsulant materials, which seal the device from moisture.
- 7Slavney, A. H.; Smaha, R. W.; Smith, I. C.; Jaffe, A.; Umeyama, D.; Karunadasa, H. I. Chemical Approaches to Addressing the Instability and Toxicity of Lead–Halide Perovskite Absorbers. Inorg. Chem. 2017, 56 (1), 46– 55, DOI: 10.1021/acs.inorgchem.6b013367https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1ynsb7P&md5=903889ff9e5b8151fb5828a98de114e0Chemical Approaches to Addressing the Instability and Toxicity of Lead-Halide Perovskite AbsorbersSlavney, Adam H.; Smaha, Rebecca W.; Smith, Ian C.; Jaffe, Adam; Umeyama, Daiki; Karunadasa, Hemamala I.Inorganic Chemistry (2017), 56 (1), 46-55CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)A review. The impressive rise in efficiencies of solar cells employing the three-dimensional (3D) lead-iodide perovskite absorbers APbI3 (A = monovalent cation) has generated intense excitement. Although these perovskites have remarkable properties as solar-cell absorbers, their potential commercialization now requires a greater focus on the materials' inherent shortcomings and environmental impact. This creates a challenge and an opportunity for synthetic chemists to address these issues through the design of new materials. Synthetic chem. offers powerful tools for manipulating the magnificent flexibility of the perovskite lattice to expand the no. of functional analogs to APbI3. To highlight improvements that should be targeted in new materials, here we discuss the intrinsic instability and toxicity of 3D lead-halide perovskites. We consider possible sources of these instabilities and propose methods to overcome them through synthetic design. We also discuss new materials developed for realizing the exceptional photophys. properties of lead-halide perovskites in more environmentally benign materials. In this Forum Article, we provide a brief overview of the field with a focus on our group's contributions to identifying and addressing problems inherent to 3D lead-halide perovskites.
- 8Nedelcu, G.; Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Grotevent, M. J.; Kovalenko, M. V. Fast Anion-Exchange in Highly Luminescent Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, I). Nano Lett. 2015, 15 (8), 5635– 5640, DOI: 10.1021/acs.nanolett.5b024048https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXht1altLrF&md5=383d30b7c4374f7d043e7098d48a8a50Fast Anion-Exchange in Highly Luminescent Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, I)Nedelcu, Georgian; Protesescu, Loredana; Yakunin, Sergii; Bodnarchuk, Maryna I.; Grotevent, Matthias J.; Kovalenko, Maksym V.Nano Letters (2015), 15 (8), 5635-5640CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Postsynthetic chem. transformations of colloidal nanocrystals, such as ion-exchange reactions, provide an avenue to compositional fine-tuning or to otherwise inaccessible materials and morphologies. While cation-exchange is facile and commonplace, anion-exchange reactions have not received substantial deployment. Report fast, low-temp., deliberately partial, or complete anion-exchange in highly luminescent semiconductor nanocrystals of perovskites CsPbX3 (X = Cl, Br, I). By adjusting the halide ratios in the colloidal nanocrystal soln., the bright luminescence can be tuned over the entire visible spectral region (410-700 nm) while maintaining high quantum yields of 20-80% and narrow emission line widths of 10-40 nm (from blue to red). Fast internanocrystal anion-exchange is demonstrated, leading to uniform CsPb(Cl/Br)3 or CsPb(Br/I)3 compns. simply by mixing CsPbCl3, CsPbBr3, and CsPbI3 nanocrystals in appropriate ratios.
- 9Bischak, C. G.; Hetherington, C. L.; Wu, H.; Aloni, S.; Ogletree, D. F.; Limmer, D. T.; Ginsberg, N. S. Origin of Reversible Photoinduced Phase Separation in Hybrid Perovskites. Nano Lett. 2017, 17 (2), 1028– 1033, DOI: 10.1021/acs.nanolett.6b044539https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslSqsrc%253D&md5=15318b3b3e477ad003302e551ccaaf37Origin of Reversible Photoinduced Phase Separation in Hybrid PerovskitesBischak, Connor G.; Hetherington, Craig L.; Wu, Hao; Aloni, Shaul; Ogletree, D. Frank; Limmer, David T.; Ginsberg, Naomi S.Nano Letters (2017), 17 (2), 1028-1033CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The distinct phys. properties of hybrid org.-inorg. materials can lead to unexpected nonequil. phenomena that are difficult to characterize due to the broad range of length and time scales involved. For instance, mixed halide hybrid perovskites are promising materials for optoelectronics, yet bulk measurements suggest the halides reversibly phase sep. upon photoexcitation. By combining nanoscale imaging and multiscale modeling, the authors find that the nature of halide demixing in these materials is distinct from macroscopic phase sepn. The authors propose that the localized strain induced by a single photoexcited charge interacting with the soft, ionic lattice is sufficient to promote halide phase sepn. and nucleate a light-stabilized, low-bandgap, ∼8 nm iodide-rich cluster. The limited extent of this polaron is essential to promote demixing because by contrast bulk strain would simply be relaxed. Photoinduced phase sepn. is therefore a consequence of the unique electromech. properties of this hybrid class of materials. Exploiting photoinduced phase sepn. and other nonequil. phenomena in hybrid materials more generally could expand applications in sensing, switching, memory, and energy storage.
- 10Stranks, S. D.; Snaith, H. J. Metal-Halide Perovskites for Photovoltaic and Light-Emitting Devices. Nat. Nanotechnol. 2015, 10 (5), 391– 402, DOI: 10.1038/nnano.2015.9010https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXnvFSqtbY%253D&md5=5911a8911c2c8cb3686acecddb114c41Metal-halide perovskites for photovoltaic and light-emitting devicesStranks, Samuel D.; Snaith, Henry J.Nature Nanotechnology (2015), 10 (5), 391-402CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)A review. Metal-halide perovskites are cryst. materials originally developed out of scientific curiosity. Unexpectedly, solar cells incorporating these perovskites are rapidly emerging as serious contenders to rival the leading photovoltaic technologies. Power conversion efficiencies have jumped from 3% to over 20% in just four years of academic research. Here, we review the rapid progress in perovskite solar cells, as well as their promising use in light-emitting devices. In particular, we describe the broad tunability and fabrication methods of these materials, the current understanding of the operation of state-of-the-art solar cells and we highlight the properties that have delivered light-emitting diodes and lasers. We discuss key thermal and operational stability challenges facing perovskites, and give an outlook of future research avenues that might bring perovskite technol. to commercialization.
- 11Smith, I. C.; Hoke, E. T.; Solis-Ibarra, D.; McGehee, M. D.; Karunadasa, H. I. A Layered Hybrid Perovskite Solar-Cell Absorber with Enhanced Moisture Stability. Angew. Chem., Int. Ed. 2014, 126 (42), 11414– 11417, DOI: 10.1002/ange.201406466There is no corresponding record for this reference.
- 12Hintermayr, V. A.; Lampe, C.; Löw, M.; Roemer, J.; Vanderlinden, W.; Gramlich, M.; Böhm, A. X.; Sattler, C.; Nickel, B.; Lohmüller, T.; Urban, A. S. Polymer Nanoreactors Shield Perovskite Nanocrystals from Degradation. Nano Lett. 2019, 19 (8), 4928– 4933, DOI: 10.1021/acs.nanolett.9b0098212https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsVSqtb3L&md5=61402187cb70571055da24fc7548a94ePolymer Nanoreactors Shield Perovskite Nanocrystals from DegradationHintermayr, Verena A.; Lampe, Carola; Loew, Maximilian; Roemer, Janina; Vanderlinden, Willem; Gramlich, Moritz; Boehm, Anton X.; Sattler, Cornelia; Nickel, Bert; Lohmueller, Theobald; Urban, Alexander S.Nano Letters (2019), 19 (8), 4928-4933CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Halide perovskite nanocrystals (NCs) have shown impressive advances, exhibiting optical properties that outpace conventional semiconductor NCs, such as near-unity quantum yields and ultrafast radiative decay rates. Nevertheless, the NCs suffer even more from stability problems at ambient conditions and due to moisture than their bulk counterparts. Herein, we report a strategy of employing polymer micelles as nanoreactors for the synthesis of methylammonium lead trihalide perovskite NCs. Encapsulated by this polymer shell, the NCs display strong stability against water degrdn. and halide ion migration. Thin films comprising these NCs exhibit a more than 15-fold increase in lifespan in comparison to unprotected NCs in ambient conditions and even survive over 75 days of complete immersion in water. Furthermore, the NCs, which exhibit quantum yields of up to 63% and tunability of the emission wavelength throughout the visible range, show no signs of halide ion exchange. Addnl., heterostructures of MAPI and MAPBr NC layers exhibit efficient Forster resonance energy transfer (FRET), revealing a strategy for optoelectronic integration.
- 13Pisoni, A.; Jaćimović, J.; Barišić, O. S.; Spina, M.; Gaál, R.; Forró, L.; Horváth, E. Ultra-Low Thermal Conductivity in Organic–Inorganic Hybrid Perovskite CH3NH3PbI3. J. Phys. Chem. Lett. 2014, 5 (14), 2488– 2492, DOI: 10.1021/jz501210913https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFSmsLrE&md5=5557212c144e57caf4cb172ae64e6850Ultra-Low Thermal Conductivity in Organic-Inorganic Hybrid Perovskite CH3NH3PbI3Pisoni, Andrea; Jacimovic, Jacim; Barisic, Osor S.; Spina, Massimo; Gaal, Richard; Forro, Laszlo; Horvath, EndreJournal of Physical Chemistry Letters (2014), 5 (14), 2488-2492CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The authors report on the temp. dependence of thermal cond. of single cryst. and polycryst. organometallic perovskite CH3NH3PbI3. The comparable abs. values and temp. dependence of the two samples' morphologies indicate the minor role of the grain boundaries on the heat transport. Theor. modeling demonstrates the importance of the resonant scattering in both specimens. The interaction between phonon waves and rotational degrees of freedom of CH3NH3+ sublattice emerges as the dominant mechanism for attenuation of heat transport and for ultralow thermal cond. of 0.5 W/(Km) at room temp.
- 14Mettan, X.; Pisoni, R.; Matus, P.; Pisoni, A.; Jaćimović, J.; Náfrádi, B.; Spina, M.; Pavuna, D.; Forró, L.; Horváth, E. Tuning of the Thermoelectric Figure of Merit of CH3NH3MI3 (M = Pb,Sn) Photovoltaic Perovskites. J. Phys. Chem. C 2015, 119 (21), 11506– 11510, DOI: 10.1021/acs.jpcc.5b0393914https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXnsFOgu70%253D&md5=acb76244c75e00b064d6e5021eb07386Tuning of the Thermoelectric Figure of Merit of CH3NH3MI3 (M= Pb, Sn) Photovoltaic PerovskitesMettan, Xavier; Pisoni, Riccardo; Matus, Peter; Pisoni, Andrea; Jacimovic, Jacim; Nafradi, Balint; Spina, Massimo; Pavuna, Davor; Forro, Laszlo; Horvath, EndreJournal of Physical Chemistry C (2015), 119 (21), 11506-11510CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The hybrid halide perovskites, the very performant compds. in photovoltaic applications, possess large Seebeck coeff. and low thermal cond., making them potentially interesting high figure of merit (ZT) materials. For this purpose, one needs to tune the elec. cond. of these semiconductors to higher values. The authors have studied the CH3NH3MI3 (M = Pb,Sn) samples in pristine form showing very low ZT values for both materials; however, photoinduced doping (in M = Pb) and chem. doping (in M = Sn) indicate that, by further doping optimization, ZT can be enhanced toward unity and reach the performance level of the presently most efficient thermoelec. materials.
- 15Lee, W.; Li, H.; Wong, A. B.; Zhang, D.; Lai, M.; Yu, Y.; Kong, Q.; Lin, E.; Urban, J. J.; Grossman, J. C.; Yang, P. Ultralow Thermal Conductivity in All-Inorganic Halide Perovskites. Proc. Natl. Acad. Sci. U.S.A. 2017, 114 (33), 8693– 8697, DOI: 10.1073/pnas.171174411415https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1CktbfO&md5=2e6fd602d4e09513f707d3346dfb86aeUltralow thermal conductivity in all-inorganic halide perovskitesLee, Woochul; Li, Huashan; Wong, Andrew B.; Zhang, Dandan; Lai, Minliang; Yu, Yi; Kong, Qiao; Lin, Elbert; Urban, Jeffrey J.; Grossman, Jeffrey C.; Yang, PeidongProceedings of the National Academy of Sciences of the United States of America (2017), 114 (33), 8693-8697CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Controlling the flow of thermal energy is crucial to numerous applications ranging from microelectronic devices to energy storage and energy conversion devices. Here, we report ultralow lattice thermal conductivities of soln.-synthesized, single-cryst. all-inorg. halide perovskite nanowires composed of CsPbI3 (0.45 ± 0.05 W·m-1·K-1), CsPbBr3 (0.42 ± 0.04 W·m-1·K-1), and CsSnI3 (0.38 ± 0.04 W·m-1·K-1). We attribute this ultralow thermal cond. to the cluster rattling mechanism, wherein strong optical-acoustic phonon scatterings are driven by a mixt. of 0D/1D/2D collective motions. Remarkably, CsSnI3 possesses a rare combination of ultralow thermal cond., high elec. cond. (282 S·cm-1), and high hole mobility (394 cm2·V-1·s-1). The unique thermal transport properties in all-inorg. halide perovskites hold promise for diverse applications such as phononic and thermoelec. devices. Furthermore, the insights obtained from this work suggest an opportunity to discover low thermal cond. materials among unexplored inorg. crystals beyond caged and layered structures.
- 16Akkerman, Q. A.; Rainò, G.; Kovalenko, M. V.; Manna, L. Genesis, Challenges and Opportunities for Colloidal Lead Halide Perovskite Nanocrystals. Nat. Mater. 2018, 17 (5), 394– 405, DOI: 10.1038/s41563-018-0018-416https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXltFOrsrw%253D&md5=33285d81190915543b01d5ddb47c2e8bGenesis, challenges and opportunities for colloidal lead halide perovskite nanocrystalsAkkerman, Quinten A.; Raino, Gabriele; Kovalenko, Maksym V.; Manna, LiberatoNature Materials (2018), 17 (5), 394-405CODEN: NMAACR; ISSN:1476-1122. (Nature Research)A review. Lead halide perovskites (LHPs) in the form of nanometer-sized colloidal crystals, or nanocrystals (NCs), have attracted the attention of diverse materials scientists due to their unique optical versatility, high photoluminescence quantum yields and facile synthesis. LHP NCs have a 'soft' and predominantly ionic lattice, and their optical and electronic properties are highly tolerant to structural defects and surface states. Therefore, they cannot be approached with the same exptl. mindset and theor. framework as conventional semiconductor NCs. In this Review, we discuss LHP NCs historical and current research pursuits, challenges in applications, and the related present and future mitigation strategies explored.
- 17Grancini, G.; Nazeeruddin, M. K. Dimensional Tailoring of Hybrid Perovskites for Photovoltaics. Nat. Rev. Mater. 2019, 4 (1), 4– 22, DOI: 10.1038/s41578-018-0065-017https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXisFSgurrJ&md5=115a8bb52a670a6302c4c69e29deaccdDimensional tailoring of hybrid perovskites for photovoltaicsGrancini, Giulia; Nazeeruddin, Mohammad KhajaNature Reviews Materials (2019), 4 (1), 4-22CODEN: NRMADL; ISSN:2058-8437. (Nature Research)A review. Hybrid perovskites are currently one of the most active fields of research owing to their enormous potential for photovoltaics. The performance of 3D hybrid org. inorg. perovskite solar cells has increased at an incredible rate, reaching power conversion efficiencies comparable to those of many established technologies. However, the com. application of 3D hybrid perovskites is inhibited by their poor stability. Relative to 3D hybrid perovskites, low dimensional i.e., 2D hybrid perovskites have demonstrated higher moisture stability, offering new approaches to stabilizing perovskite based photovoltaic devices. Furthermore, 2D hybrid perovskites have versatile structures, enabling the fine tuning of their optoelectronic properties through compositional engineering. In this Review, we discuss the state of the art in 2D perovskites, providing an overview of structural and materials engineering aspects and optical and photophys. properties. Moreover, we discuss recent developments along with the main limitations of 3D perovskites and assess the advantages of 2D perovskites over their 3D parent structures in terms of stability. Finally, we review recent achievements in combining 3D and 2D perovskites as an approach to simultaneously boost device efficiency and stability, paving the way for mixed dimensional perovskite solar cells for com. applications.
- 18Miyata, K.; Meggiolaro, D.; Trinh, M. T.; Joshi, P. P.; Mosconi, E.; Jones, S. C.; Angelis, F. D.; Zhu, X.-Y. Large Polarons in Lead Halide Perovskites. Sci. Adv. 2017, 3 (8), e1701217 DOI: 10.1126/sciadv.170121718https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXntFGrs7s%253D&md5=817f24c41acd1772e370cc59df0c6c4cLarge polarons in lead halide perovskitesMiyata, Kiyoshi; Meggiolaro, Daniele; Trinh, M. Tuan; Joshi, Prakriti P.; Mosconi, Edoardo; Jones, Skyler C.; De Angelis, Filippo; Zhu, X.-Y.Science Advances (2017), 3 (8), e1701217/1-e1701217/9CODEN: SACDAF; ISSN:2375-2548. (American Association for the Advancement of Science)Lead halide perovskites show marked defect tolerance responsible for their excellent optoelectronic properties. These properties might be explained by the formation of large polarons, but how they are formed and whether org. cations are essential remain open questions. We provide a direct time domain view of large polaron formation in single-crystal lead bromide perovskites CH3NH3PbBr3 and CsPbBr3. We found that large polaron forms predominantly from the deformation of the PbBr3-_frameworks, irresp. of the cation type. The difference lies in the polaron formation time, which, in CH3NH3PbBr3 (0.3 ps), is less than half of that in CsPbBr3 (0.7 ps). First-principles calcns. confirm large polaron formation, identify the Pb-Br-Pb deformation modes as responsible, and explain quant. the rate difference between CH3NH3PbBr3 and CsPbBr3. The findings reveal the general advantage of the soft [PbX3]- sublattice in charge carrier protection and suggest that there is likely no mechanistic limitations in using all-inorg. or mixed-cation lead halide perovskites to overcome instability problems and to tune the balance between charge carrier protection and mobility.
- 19Miyata, K.; Atallah, T. L.; Zhu, X.-Y. Lead Halide Perovskites: Crystal-Liquid Duality, Phonon Glass Electron Crystals, and Large Polaron Formation. Sci. Adv. 2017, 3 (10), e1701469 DOI: 10.1126/sciadv.170146919https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXls1Gmtrg%253D&md5=5452e05b702672f76a2ba4e75386322aLead halide perovskites: Crystal-liquid duality, phonon glass electron crystals, and large polaron formationMiyata, Kiyoshi; Atallah, Timothy L.; Zhu, X.-Y.Science Advances (2017), 3 (10), e1701469/1-e1701469/10CODEN: SACDAF; ISSN:2375-2548. (American Association for the Advancement of Science)Lead halide perovskites have been demonstrated as high performance materials in solar cells and light-emitting devices. These materials are characterized by coherent band transport expected from cryst. semiconductors, but dielec. responses and phonon dynamics typical of liqs. This "crystal-liq." duality implies that lead halide perovskites belong to phonon glass electron crystals, a class of materials believed to make the most efficient thermoelecs.We show that the crystal-liq. duality and the resulting dielec. response are responsible for large polaron formation and screening of charge carriers, leading to defect tolerance, moderate charge carrier mobility, and radiative recombination properties. Large polaron formation, along with the phonon glass character,may also explain the marked redn. in hot carrier cooling rates in these materials.
- 20Beecher, A. N.; Semonin, O. E.; Skelton, J. M.; Frost, J. M.; Terban, M. W.; Zhai, H.; Alatas, A.; Owen, J. S.; Walsh, A.; Billinge, S. J. L. Direct Observation of Dynamic Symmetry Breaking above Room Temperature in Methylammonium Lead Iodide Perovskite. ACS Energy Lett. 2016, 1 (4), 880– 887, DOI: 10.1021/acsenergylett.6b0038120https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFeku7bE&md5=9e4dae5239a4767989640330645a2f8eDirect Observation of Dynamic Symmetry Breaking above Room Temperature in Methylammonium Lead Iodide PerovskiteBeecher, Alexander N.; Semonin, Octavi E.; Skelton, Jonathan M.; Frost, Jarvist M.; Terban, Maxwell W.; Zhai, Haowei; Alatas, Ahmet; Owen, Jonathan S.; Walsh, Aron; Billinge, Simon J. L.ACS Energy Letters (2016), 1 (4), 880-887CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)Lead halide perovskites such as methylammonium lead triiodide (CH3NH3PbI3) have outstanding optical and electronic properties for photovoltaic applications, yet a full understanding of how this soln.-processable material works so well is currently missing. Previous research has revealed that CH3NH3PbI3 possesses multiple forms of static disorder regardless of prepn. method, which is surprising in light of its excellent performance. Using high energy resoln. inelastic X-ray (HERIX) scattering, we measure phonon dispersions in CH3NH3PbI3 and find direct evidence for another form of disorder in single crystals: large-amplitude anharmonic zone edge rotational instabilities of the PbI6 octahedra that persist to room temp. and above, left over from structural phase transitions that take place tens to hundreds of degrees below. Phonon calcns. show that the orientations of the methylammonium (CH3NH3+) couple strongly and cooperatively to these modes. The result is a noncentrosym., instantaneous local structure, which we observe in at. pair distribution function (PDF) measurements. This local symmetry breaking is unobservable by Bragg diffraction but can explain key material properties such as the structural phase sequence, ultralow thermal transport, and large minority charge carrier lifetimes despite moderate carrier mobility. From the PDF we est. the size of the fluctuating symmetry broken domains to be between 1 and 3 nm in diam.
- 21Cottingham, P.; Brutchey, R. L. Depressed Phase Transitions and Thermally Persistent Local Distortions in CsPbBr3 Quantum Dots. Chem. Mater. 2018, 30 (19), 6711– 6716, DOI: 10.1021/acs.chemmater.8b0229521https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhs1ygtLfE&md5=2a7f6b278a8f4cc49ac46b3eaf186051Depressed Phase Transitions and Thermally Persistent Local Distortions in CsPbBr3 Quantum DotsCottingham, Patrick; Brutchey, Richard L.Chemistry of Materials (2018), 30 (19), 6711-6716CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The optoelectronic properties of CsPbX3 quantum dots (where X = Cl, Br, or I) are influenced by both their local and av. structures. Variable-temp. synchrotron X-ray diffraction measurements of CsPbBr3 quantum dots show that the temps. for both the orthorhombic-to-tetragonal (50 °C < Tγ-β < 59 °C) and tetragonal-to-cubic (108 °C < Tβ-α < 117 °C) phase transitions of the av. structure are depressed relative to their temps. in bulk CsPbBr3. Simultaneously, pair distribution function anal. of synchrotron X-ray total scattering measurements indicates that the local crystal structure of the quantum dots is best described as orthorhombically distorted over the temp. range of 22 °C < T < 160 °C, with only small changes in the magnitude of the distortion occurring during the obsd. changes in the av. structure. Taken together, these results suggest that phase transitions in CsPbBr3 quantum dots are order-disorder, involving the gradual ordering of individually coherent domains that cannot be attributed to changes in the surface area or to ferroelec. phenomena.
- 22Yaffe, O.; Guo, Y.; Tan, L. Z.; Egger, D. A.; Hull, T.; Stoumpos, C. C.; Zheng, F.; Heinz, T. F.; Kronik, L.; Kanatzidis, M. G.; Owen, J. S.; Rappe, A. M.; Pimenta, M. A.; Brus, L. E. Local Polar Fluctuations in Lead Halide Perovskite Crystals. Phys. Rev. Lett. 2017, 118 (13), 136001, DOI: 10.1103/PhysRevLett.118.13600122https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFeju7zK&md5=7df46b915456003e801e23349fef1e55Local polar fluctuations in lead halide perovskite crystalsYaffe, Omer; Guo, Yinsheng; Tan, Liang Z.; Egger, David A.; Hull, Trevor; Stoumpos, Constantinos C.; Zheng, Fan; Heinz, Tony F.; Kronik, Leeor; Kanatzidis, Mercouri G.; Owen, Jonathan S.; Rappe, Andrew M.; Pimenta, Marcos A.; Brus, Louis E.Physical Review Letters (2017), 118 (13), 136001/1-136001/6CODEN: PRLTAO; ISSN:1079-7114. (American Physical Society)Hybrid lead-halide perovskites have emerged as an excellent class of photovoltaic materials. Recent reports suggest that the org. mol. cation is responsible for local polar fluctuations that inhibit carrier recombination. We combine low-frequency Raman scattering with first-principles mol. dynamics (MD) to study the fundamental nature of these local polar fluctuations. Our observations of a strong central peak in the cubic phase of both hybrid (CH3NH3PbBr3) and all-inorg. (CsPbBr3) leadhalide perovskites show that anharmonic, local polar fluctuations are intrinsic to the general lead-halide perovskite structure, and not unique to the dipolar org. cation. MD simulations indicate that head-tohead Cs motion coupled to Br face expansion, occurring on a few hundred femtosecond time scale, drives the local polar fluctuations in CsPbBr3.
- 23Bertolotti, F.; Protesescu, L.; Kovalenko, M. V.; Yakunin, S.; Cervellino, A.; Billinge, S. J. L.; Terban, M. W.; Pedersen, J. S.; Masciocchi, N.; Guagliardi, A. Coherent Nanotwins and Dynamic Disorder in Cesium Lead Halide Perovskite Nanocrystals. ACS Nano 2017, 11 (4), 3819– 3831, DOI: 10.1021/acsnano.7b0001723https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXlvVKjsLk%253D&md5=593da980a5192e38c74b2b79152bf3fcCoherent Nanotwins and Dynamic Disorder in Cesium Lead Halide Perovskite NanocrystalsBertolotti, Federica; Protesescu, Loredana; Kovalenko, Maksym V.; Yakunin, Sergii; Cervellino, Antonio; Billinge, Simon J. L.; Terban, Maxwell W.; Pedersen, Jan Skov; Masciocchi, Norberto; Guagliardi, AntoniettaACS Nano (2017), 11 (4), 3819-3831CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Crystal defects in highly luminescent colloidal nanocrystals (NCs) of CsPbX3 perovskites (X = Cl, Br, I) are investigated. Using X-ray total scattering techniques and the Debye scattering equation (DSE), the authors provide evidence that the local structure of these NCs always exhibits orthorhombic tilting of PbX6 octahedra within locally ordered subdomains. These subdomains are hinged through a two-/three-dimensional (2D/3D) network of twin boundaries through which the coherent arrangement of the Pb ions throughout the whole NC is preserved. The d. of these twin boundaries dets. the size of the subdomains and results in an apparent higher-symmetry structure on av. in the high-temp. modification. Dynamic cooperative rotations of PbX6 octahedra are likely at work at the twin boundaries, causing the rearrangement of the 2D or 3D network, particularly effective in the pseudocubic phases. An orthorhombic, 3D γ-phase, isostructural to that of CsPbBr3 is found here in as-synthesized CsPbI3 NCs.
- 24Gu, H.-Y.; Yin, W.-J.; Gong, X.-G. Significant Phonon Anharmonicity Drives Phase Transitions in CsPbI3. Appl. Phys. Lett. 2021, 119 (19), 191101, DOI: 10.1063/5.007236724https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXisVegs7vK&md5=a83c4c2b94add72b47c72976ebd605e7Significant phonon anharmonicity drives phase transitions in CsPbI3Gu, Hong-Yang; Yin, Wan-Jian; Gong, Xin-GaoApplied Physics Letters (2021), 119 (19), 191101CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Due to its high chem. stability and high power conversion efficiency as a solar cell absorber, the inorg. halide perovskite, CsPbI3, is considered 1 of the most promising competitors to its hybrid org.-inorg. counterpart, MeNH3PbI3. The phase transition from the photoactive black phase to the inactive yellow phase is a remarkable limitation that harms long-term phase stability. The phase transitions follow different pathways as the temp. increases and/or decreases, a phenomenon that is anomalous and remains poorly understood. The temp.-dependent free energy of CsPbI3 was systematically calcd. in different crystal phases (α, β, γ, δ) by considering the phonon contribution to the Gibbs free energy. The free energy results from calcns. that include harmonic phonons cannot reproduce exptl. observations. Alternatively, the renormalized phonon quasiparticle approach was used to derive the free energies of different CsPbI3 phases at finite temps. Based on these calcd. free energies, whose derivations included the anharmonic effect, phase-transition processes consistent with exptl. results were obsd. The anal. of the temp. effect on the phonon frequencies demonstrated that anharmonic effects in the CsPbI3 had a significant influence on its phase transitions. (c) 2021 American Institute of Physics.
- 25Lai, M.; Obliger, A.; Lu, D.; Kley, C. S.; Bischak, C. G.; Kong, Q.; Lei, T.; Dou, L.; Ginsberg, N. S.; Limmer, D. T.; Yang, P. Intrinsic Anion Diffusivity in Lead Halide Perovskites Is Facilitated by a Soft Lattice. Proc. Natl. Acad. Sci. U. S. A. 2018, 115 (47), 11929– 11934, DOI: 10.1073/pnas.181271811525https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXit1CrtrrI&md5=80e914062b1e2f581e624b7db9d7f852Intrinsic anion diffusivity in lead halide perovskites is facilitated by soft latticeLai, Minliang; Obliger, Amael; Lu, Dylan; Kley, Christopher S.; Bischak, Connor G.; Kong, Qiao; Lei, Teng; Dou, Letian; Ginsberg, Naomi S.; Limmer, David T.; Yang, PeidongProceedings of the National Academy of Sciences of the United States of America (2018), 115 (47), 11929-11934CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Facile ionic transport in lead halide perovskites plays a crit. role in device performance. Understanding the microscopic origins of high ionic conductivities has been complicated by indirect measurements and sample microstructural heterogeneities. Here, we report the direct visualization of halide anion interdiffusion in CsPbCl3, CsPbBr3 single cryst. perovskite nanowire heterojunctions using wide-field and confocal photoluminescence measurements. The combination of nanoscale imaging techniques with these single cryst. materials allows us to measure intrinsic anionic lattice diffusivities, free from complications of microscale inhomogeneity. Halide diffusivities were found to be around cm2/s at about 100° C, which are several orders of magnitudes lower than those reported in polycryst. thin films. Spatially resolved photoluminescence lifetimes and surface potential measurements provide evidence of the central role of halide vacancies in facilitating ionic diffusion. Vacancy formation free energies computed from mol. simulation are small due to the easily deformable perovskite lattice, accounting for the high equil. vacancy concn. Furthermore, mol. simulations suggest that ionic motion is facilitated by low-frequency lattice modes, resulting in low activation barriers for vacancy-mediated transport. This work elucidates the intrinsic solid-state ion diffusion mechanisms in this class of semisoft materials and offers guidelines for engineering materials with long-term stability in functional devices.
- 26Cannelli, O.; Colonna, N.; Puppin, M.; Rossi, T. C.; Kinschel, D.; Leroy, L. M. D.; Löffler, J.; Budarz, J. M.; March, A. M.; Doumy, G.; Al Haddad, A.; Tu, M.-F.; Kumagai, Y.; Walko, D.; Smolentsev, G.; Krieg, F.; Boehme, S. C.; Kovalenko, M. V.; Chergui, M.; Mancini, G. F. Quantifying Photoinduced Polaronic Distortions in Inorganic Lead Halide Perovskite Nanocrystals. J. Am. Chem. Soc. 2021, 143 (24), 9048– 9059, DOI: 10.1021/jacs.1c0240326https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhtF2ktr7J&md5=79e4f2bc9941e64adb641eda25407c1aQuantifying Photoinduced Polaronic Distortions in Inorganic Lead Halide Perovskite NanocrystalsCannelli, Oliviero; Colonna, Nicola; Puppin, Michele; Rossi, Thomas C.; Kinschel, Dominik; Leroy, Ludmila M. D.; Loffler, Janina; Budarz, James M.; March, Anne Marie; Doumy, Gilles; Al Haddad, Andre; Tu, Ming-Feng; Kumagai, Yoshiaki; Walko, Donald; Smolentsev, Grigory; Krieg, Franziska; Boehme, Simon C.; Kovalenko, Maksym V.; Chergui, Majed; Mancini, Giulia F.Journal of the American Chemical Society (2021), 143 (24), 9048-9059CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The development of next-generation perovskite-based optoelectronic devices relies critically on the understanding of the interaction between charge carriers and the polar lattice in out-of-equil. conditions. While it has become increasingly evident for CsPbBr3 perovskites that the Pb-Br framework flexibility plays a key role in their light-activated functionality, the corresponding local structural rearrangement has not yet been unambiguously identified. In this work, we demonstrate that the photoinduced lattice changes in the system are due to a specific polaronic distortion, assocd. with the activation of a longitudinal optical phonon mode at 18 meV by electron-phonon coupling, and we quantify the assocd. structural changes with at.-level precision. Key to this achievement is the combination of time-resolved and temp.-dependent studies at Br K and Pb L3 X-ray absorption edges with refined ab initio simulations, which fully account for the screened core-hole final state effects on the X-ray absorption spectra. From the temporal kinetics, we show that carrier recombination reversibly unlocks the structural deformation at both Br and Pb sites. The comparison with the temp.-dependent XAS results rules out thermal effects as the primary source of distortion of the Pb-Br bonding motif during photoexcitation. Our work provides a comprehensive description of the CsPbBr3 perovskites' photophysics, offering novel insights on the light-induced response of the system and its exceptional optoelectronic properties.
- 27Hirotsu, S.; Harada, J.; Iizumi, M.; Gesi, K. Structural Phase Transitions in CsPbBr3. J. Phys. Soc. Jpn. 1974, 37 (5), 1393– 1398, DOI: 10.1143/JPSJ.37.139327https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2MXhtVWntA%253D%253D&md5=0841c7d06336c0e85933b61f74f94192Structural phase transitions in cesium tribromoplumbateHirotsu, Shunsuke; Harada, Jimpei; Iizumi, Masashi; Gesi, KazuoJournal of the Physical Society of Japan (1974), 37 (5), 1393-8CODEN: JUPSAU; ISSN:0031-9015.Structural phase transitions in perovskite-type CsPbBr3 were investigated by neutron diffraction. Phase transitions occur at 88° and 130°, which are 2nd and 1st-order, resp. The phase transition at 130° is caused by condensation of the M3 mode at the M point of the cubic Brillouin zone, while the one at 88° results from condensation of the doubly degenerate R25-like mode (Z9 mode) at the Z point of the tetragonal Brillouin zone. Group theor. considerations based on these results reveal that the crystal transforms from cubic perovskite structure (Pm3m) to tetragonal (P4/mbm) at 130° and further to orthorhombic (D162h-Pmbn) at 88°. Possible at. displacements induced at the phase transitions are obtained from the eigenvectors of the condensing modes.
- 28Stoumpos, C. C.; Malliakas, C. D.; Peters, J. A.; Liu, Z.; Sebastian, M.; Im, J.; Chasapis, T. C.; Wibowo, A. C.; Chung, D. Y.; Freeman, A. J.; Wessels, B. W.; Kanatzidis, M. G. Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation Detection. Cryst. Growth Des. 2013, 13 (7), 2722– 2727, DOI: 10.1021/cg400645t28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXosFyitLc%253D&md5=615d4e50e40aa9c8cb77e787ec333bb9Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation DetectionStoumpos, Constantinos C.; Malliakas, Christos D.; Peters, John A.; Liu, Zhifu; Sebastian, Maria; Im, Jino; Chasapis, Thomas C.; Wibowo, Arief C.; Chung, Duck Young; Freeman, Arthur J.; Wessels, Bruce W.; Kanatzidis, Mercouri G.Crystal Growth & Design (2013), 13 (7), 2722-2727CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)The synthesis, crystal growth, and structural and optoelectronic characterization was carried out for the perovskite compd. CsPbBr3. This compd. is a direct band gap semiconductor which meets most of the requirements for successful detection of X- and γ-ray radiation, such as high attenuation, high resistivity, and significant photocond. response, with detector resoln. comparable to that of com., state-of-the-art materials. A structural phase transition which occurs during crystal growth at higher temp. does not seem to affect its crystal quality. Its μτ product for both hole and electron carriers is approx. equal. The μτ product for electrons is comparable to Cd Zn telluride (CZT) and that for holes is 10 times higher than CZT.
- 29Møller, C. K. The Structure of Perovskite-like Caesium Plumbo Trihalides. Mater. Fys. Medd Danske Vidensk Selsk. 1959, 32 (2).There is no corresponding record for this reference.
- 30Vanacore, G. M.; Hu, J.; Liang, W.; Bietti, S.; Sanguinetti, S.; Zewail, A. H. Diffraction of Quantum Dots Reveals Nanoscale Ultrafast Energy Localization. Nano Lett. 2014, 14 (11), 6148– 6154, DOI: 10.1021/nl502293a30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht12gur3M&md5=e89125acc39ab25a56daef9c0cd5336eDiffraction of Quantum Dots Reveals Nanoscale Ultrafast Energy LocalizationVanacore, Giovanni M.; Hu, Jianbo; Liang, Wenxi; Bietti, Sergio; Sanguinetti, Stefano; Zewail, Ahmed H.Nano Letters (2014), 14 (11), 6148-6154CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Unlike in bulk materials, energy transport in low-dimensional and nanoscale systems may be governed by a coherent ballistic behavior of lattice vibrations, the phonons. If dominant, such behavior would det. the mechanism for transport and relaxation in various energy-conversion applications. To study this coherent limit, both the spatial and temporal resolns. must be sufficient for the length-time scales involved. The lattice dynamics in nanoscale quantum dots of GaAs was obsd. using ultrafast electron diffraction. By varying the dot size h = 11-46 nm, the length scale effect was examd., together with the temporal change. When the dot size is smaller than the inelastic phonon mean-free path, the energy remains localized in high-energy acoustic modes that travel coherently within the dot. As the dot size increases, an energy dissipation toward low-energy phonons takes place, and the transport becomes diffusive. Because ultrafast diffraction provides the at.-scale resoln. and a sufficiently high time resoln., other nanostructured materials can be studied similarly to elucidate the nature of dynamical energy localization.
- 31Krieg, F.; Ochsenbein, S. T.; Yakunin, S.; ten Brinck, S.; Aellen, P.; Süess, A.; Clerc, B.; Guggisberg, D.; Nazarenko, O.; Shynkarenko, Y.; Kumar, S.; Shih, C.-J.; Infante, I.; Kovalenko, M. V. Colloidal CsPbX3 (X = Cl, Br, I) Nanocrystals 2.0: Zwitterionic Capping Ligands for Improved Durability and Stability. ACS Energy Lett. 2018, 3 (3), 641– 646, DOI: 10.1021/acsenergylett.8b0003531https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXisFGrsb8%253D&md5=0f121a35e9b73499855b8799d667d8f2Colloidal CsPbX3 (X = Cl, Br, I) Nanocrystals 2.0: Zwitterionic Capping Ligands for Improved Durability and StabilityKrieg, Franziska; Ochsenbein, Stefan T.; Yakunin, Sergii; ten Brinck, Stephanie; Aellen, Philipp; Suess, Adrian; Clerc, Baptiste; Guggisberg, Dominic; Nazarenko, Olga; Shynkarenko, Yevhen; Kumar, Sudhir; Shih, Chih-Jen; Infante, Ivan; Kovalenko, Maksym V.ACS Energy Letters (2018), 3 (3), 641-646CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and optoelectronic applications are hampered by the loss of colloidal stability and structural integrity due to the facile desorption of surface capping mols. during isolation and purifn. To address this issue, herein, we propose a new ligand capping strategy utilizing common and inexpensive long-chain zwitterionic mols. such as 3-(N,N-dimethyloctadecylammonio)propanesulfonate, resulting in much improved chem. durability. In particular, this class of ligands allows for the isolation of clean NCs with high photoluminescence quantum yields (PL QYs) of above 90% after four rounds of pptn./redispersion along with much higher overall reaction yields of uniform and colloidal dispersible NCs. Densely packed films of these NCs exhibit high PL QY values and effective charge transport. Consequently, they exhibit photocond. and low thresholds for amplified spontaneous emission of 2 μJ cm-2 under femtosecond optical excitation and are suited for efficient light-emitting diodes.
- 32Guzelturk, B.; Utterback, J. K.; Coropceanu, I.; Kamysbayev, V.; Janke, E. M.; Zajac, M.; Yazdani, N.; Cotts, B. L.; Park, S.; Sood, A.; Lin, M.-F.; Reid, A. H.; Kozina, M. E.; Shen, X.; Weathersby, S. P.; Wood, V.; Salleo, A.; Wang, X.; Talapin, D. V.; Ginsberg, N. S.; Lindenberg, A. M. Nonequilibrium Thermodynamics of Colloidal Gold Nanocrystals Monitored by Ultrafast Electron Diffraction and Optical Scattering Microscopy. ACS Nano 2020, 14 (4), 4792– 4804, DOI: 10.1021/acsnano.0c0067332https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXls12itLk%253D&md5=b3bf9b6e4afbebb7115212da17d2ac23Nonequilibrium Thermodynamics of Colloidal Gold Nanocrystals Monitored by Ultrafast Electron Diffraction and Optical Scattering MicroscopyGuzelturk, Burak; Utterback, James K.; Coropceanu, Igor; Kamysbayev, Vladislav; Janke, Eric M.; Zajac, Marc; Yazdani, Nuri; Cotts, Benjamin L.; Park, Suji; Sood, Aditya; Lin, Ming-Fu; Reid, Alexander H.; Kozina, Michael E.; Shen, Xiaozhe; Weathersby, Stephen P.; Wood, Vanessa; Salleo, Alberto; Wang, Xijie; Talapin, Dmitri V.; Ginsberg, Naomi S.; Lindenberg, Aaron M.ACS Nano (2020), 14 (4), 4792-4804CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Metal nanocrystals exhibit important optoelectronic and photocatalytic functionalities in response to light. These dynamic energy conversion processes have been commonly studied by transient optical probes to date, but an understanding of the atomistic response following photoexcitation has remained elusive. Here, we use femtosecond resoln. electron diffraction to investigate transient lattice responses in optically excited colloidal gold nanocrystals, revealing the effects of nanocrystal size and surface ligands on the electron-phonon coupling and thermal relaxation dynamics. First, we uncover a strong size effect on the electron-phonon coupling, which arises from reduced dielec. screening at the nanocrystal surfaces and prevails independent of the optical excitation mechanism (i.e., inter- and intraband). Second, we find that surface ligands act as a tuning parameter for hot carrier cooling. Particularly, gold nanocrystals with thiol-based ligands show significantly slower carrier cooling as compared to amine-based ligands under intraband optical excitation due to electronic coupling at the nanocrystal/ligand interfaces. Finally, we spatiotemporally resolve thermal transport and heat dissipation in photoexcited nanocrystal films by combining electron diffraction with stroboscopic elastic scattering microscopy. Taken together, we resolve the distinct thermal relaxation time scales ranging from 1 ps to 100 ns assocd. with the multiple interfaces through which heat flows at the nanoscale. Our findings provide insights into optimization of gold nanocrystals and their thin films for photocatalysis and thermoelec. applications.
- 33Mancini, G. F.; Pennacchio, F.; Latychevskaia, T.; Reguera, J.; Stellacci, F.; Carbone, F. Local Photo-Mechanical Stiffness Revealed in Gold Nanoparticles Supracrystals by Ultrafast Small-Angle Electron Diffraction. Structural Dynamics 2019, 6 (2), 024304, DOI: 10.1063/1.509185833https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXntlertbc%253D&md5=1e9813db0cd7d46b7d1c104f42fec29bLocal photo-mechanical stiffness revealed in gold nanoparticles supracrystals by ultrafast small-angle electron diffractionMancini, Giulia Fulvia; Pennacchio, Francesco; Latychevskaia, Tatiana; Reguera, Javier; Stellacci, Francesco; Carbone, FabrizioStructural Dynamics (2019), 6 (2), 024304/1-024304/6CODEN: SDTYAE; ISSN:2329-7778. (American Institute of Physics)We demonstrate that highly ordered two-dimensional crystals of ligand-capped gold nanoparticles display a local photo-mech. stiffness as high as that of solids such as graphite. In out-of-equil. electron diffraction expts., a strong temp. jump is induced in a thin film with a femtosecond laser pulse. The initial electronic excitation transfers energy to the underlying structural degrees of freedom, with a rate generally proportional to the stiffness of the material. Using femtosecond small-angle electron diffraction, we observe the temporal evolution of the diffraction feature assocd. with the nearest-neighbor nanoparticle distance. The Debye-Waller decay for the octanethiol-capped nanoparticle supracrystal, in particular, is found to be unexpectedly fast, almost as fast as the stiffest solid known and obsd. by the same technique, i.e., graphite. Our observations unravel that local stiffness in a dense supramol. assembly can be created by van der Waals interactions up to a level comparable to cryst. systems characterized by covalent bonding. (c) 2019 American Institute of Physics.
- 34Hirotsu, S.; Suzuki, T.; Sawada, S. Ultrasonic Velocity around the Successive Phase Transition Points of CsPbBr3. J. Phys. Soc. Jpn. 1977, 43 (2), 575– 582, DOI: 10.1143/JPSJ.43.57534https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2sXlt1Gmt7o%253D&md5=e9dfcc1eb21a7bca21a85979a9abc172Ultrasonic velocity around the successive phase transition points of cesium lead bromide (CsPbBr3)Hirotsu, Shunsuke; Suzuki, Tomonobu; Sawada, ShozoJournal of the Physical Society of Japan (1977), 43 (2), 575-82CODEN: JUPSAU; ISSN:0031-9015.Sound velocities in perovskite-type crystal CsPbBr3 were measured around the structural phase transition points at 88 and 130°. "Detwinned" samples were used, which made it possible to relate the measured velocities to the elastic consts. in each phase. The velocities of c11 and c11-c12 modes exhibit large anomalies above and below the 2 transition points, whereas that of c44 mode is almost independent of temp. of phenomenol. and fluctuation theories. Temp. dependence of the velocity of c11 mode just above the higher transition point is consistent with the prediction from the fluctuation theory.
- 35Bechtel, J. S.; Thomas, J. C.; Van der Ven, A. Finite-Temperature Simulation of Anharmonicity and Octahedral Tilting Transitions in Halide Perovskites. Phys. Rev. Mater. 2019, 3 (11), 113605, DOI: 10.1103/PhysRevMaterials.3.11360535https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhvF2ksbo%253D&md5=f9a35f5dbd4b8d3250a1e34096149d8fFinite-temperature simulation of anharmonicity and octahedral tilting transitions in halide perovskitesBechtel, Jonathon S.; Thomas, John C.; Van der Ven, AntonPhysical Review Materials (2019), 3 (11), 113605CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)Octahedral tilting transitions are obsd. in most inorg. halide perovskites and play an important role in detg. their functional and thermodn. properties. Despite existing near room temp., the cubic and tetragonal forms of halide perovskites become dynamically unstable at low temp., making it impossible to study their thermodn. properties with commonly used quasiharmonic models. An anharmonic vibrational Hamiltonian is constructed that accurately reproduces the low-energy portion of the potential-energy surface of the halide perovskite CsPbBr3. The Hamiltonian is validated using a large first-principles dataset of energies calcd. within d. functional theory for large-amplitude deformations of the CsPbBr3 crystal. Monte Carlo simulations performed on the Hamiltonian reproduce the orthorhombic-tetragonal-cubic phase transitions obsd. in CsPbBr3 and many other halide perovskites, demonstrating the importance of anharmonic vibrational excitations in stabilizing the tetragonal and cubic phases in these materials. Measures of local structure and octahedral tilting in the cubic and tetragonal phases, obtained from Monte Carlo simulations, confirm the connection between large anisotropic displacement factors and octahedral tilting, as obsd. exptl.
- 36Dove, M. T. Theory of Displacive Phase Transitions in Minerals. Am. Mineral. 1997, 82 (3–4), 213– 244, DOI: 10.2138/am-1997-3-40136https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXjtFGnsr0%253D&md5=104931387037e9cc395d96b9294b1fadTheory of displacive phase transitions in mineralsDove, Martin T.American Mineralogist (1997), 82 (3-4), 213-244CODEN: AMMIAY; ISSN:0003-004X. (Mineralogical Society of America)A review with 231 refs. A lattice-dynamical treatment of displacive phase transitions leads naturally to the soft-mode model, in which the phase-transition mechanism involves a phonon frequency that falls to zero at the transition temp. The basic ideas of this approach are reviewed in relation to displacive phase transitions in silicates. A simple free-energy model is used to demonstrate that Landau theory gives a good approxn. to the free energy of the transition, provided that the entropy is primarily produced by the phonons rather than any configurational disorder. The "rigid unit mode" model provides a phys. link between the theory and the chem. bonds in silicates and this allows us to understand the origin of the transition temp. and also validates the application of the soft-mode model. The model is also used to reappraise the nature of the structures of high-temp. phases. Several issues that remain open, such as the origin of first-order phase transitions and the thermodn. of pressure-induced phase transitions, are discussed.
- 37Mannino, G.; Deretzis, I.; Smecca, E.; La Magna, A.; Alberti, A.; Ceratti, D.; Cahen, D. Temperature-Dependent Optical Band Gap in CsPbBr3, MAPbBr3, and FAPbBr3 Single Crystals. J. Phys. Chem. Lett. 2020, 11 (7), 2490– 2496, DOI: 10.1021/acs.jpclett.0c0029537https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXksFajtrw%253D&md5=0eb961f1f2a411b93890b8c25e85fa5cTemperature-Dependent Optical Band Gap in CsPbBr3, MAPbBr3, and FAPbBr3 Single CrystalsMannino, Giovanni; Deretzis, Ioannis; Smecca, Emanuele; La Magna, Antonino; Alberti, Alessandra; Ceratti, Davide; Cahen, DavidJournal of Physical Chemistry Letters (2020), 11 (7), 2490-2496CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Single crystals represent a benchmark for understanding the bulk properties of halide perovskites. The dielec. functions were studied of lead bromide perovskite single crystals (MAPbBr3, CsPbBr3 and FAPbBr3) by ellipsometry at 1-5 eV while varying the temp. 183-440 K. An extremely low absorption coeff. in the sub-band gap region was found, indicating the high optical quality of all 3 crystals. The band gap values were extd. through crit. point anal. showing that Tauc-based values are systematically underestimated. The 2 structural phase transitions, i.e., orthorhombic-tetragonal and tetragonal-cubic, show distinct optical behaviors, with the former having a discontinuous character. The cross-correlation of optical data with DFT calcns. evidences the role of octahedral tilting in tailoring the value of the band gap at a given temp., whereas differences in the thermal expansion affect the slope of the band gap trend as a function of temp.
- 38Momma, K.; Izumi, F. VESTA 3 for Three-Dimensional Visualization of Crystal, Volumetric and Morphology Data. J. Appl. Crystallogr. 2011, 44 (6), 1272– 1276, DOI: 10.1107/S002188981103897038https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFSisrvP&md5=885fbd9420ed18838813d6b0166f4278VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology dataMomma, Koichi; Izumi, FujioJournal of Applied Crystallography (2011), 44 (6), 1272-1276CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)VESTA is a 3D visualization system for crystallog. studies and electronic state calcns. It was upgraded to the latest version, VESTA 3, implementing new features including drawing the external morphpol. of crysals; superimposing multiple structural models, volumetric data and crystal faces; calcn. of electron and nuclear densities from structure parameters; calcn. of Patterson functions from the structure parameters or volumetric data; integration of electron and nuclear densities by Voronoi tessellation; visualization of isosurfaces with multiple levels, detn. of the best plane for selected atoms; an extended bond-search algorithm to enable more sophisticated searches in complex mols. and cage-like structures; undo and redo is graphical user interface operations; and significant performance improvements in rendering isosurfaces and calcg. slices.
- 39VandeVondele, J.; Krack, M.; Mohamed, F.; Parrinello, M.; Chassaing, T.; Hutter, J. Quickstep: Fast and Accurate Density Functional Calculations Using a Mixed Gaussian and Plane Waves Approach. Comput. Phys. Commun. 2005, 167 (2), 103– 128, DOI: 10.1016/j.cpc.2004.12.01439https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXjt1aitb4%253D&md5=8c5393031c9dbd341e0e73fcdacad486QUICKSTEP: fast and accurate density functional calculations using a mixed Gaussian and plane waves approachVandeVondele, Joost; Krack, Matthias; Mohamed, Fawzi; Parrinello, Michele; Chassaing, Thomas; Hutter, JuergComputer Physics Communications (2005), 167 (2), 103-128CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)We present the Gaussian and plane waves (GPW) method and its implementation in which is part of the freely available program package CP2K. The GPW method allows for accurate d. functional calcns. in gas and condensed phases and can be effectively used for mol. dynamics simulations. We show how derivs. of the GPW energy functional, namely ionic forces and the Kohn-Sham matrix, can be computed in a consistent way. The computational cost of computing the total energy and the Kohn-Sham matrix is scaling linearly with the system size, even for condensed phase systems of just a few tens of atoms. The efficiency of the method allows for the use of large Gaussian basis sets for systems up to 3000 atoms, and we illustrate the accuracy of the method for various basis sets in gas and condensed phases. Agreement with basis set free calcns. for single mols. and plane wave based calcns. in the condensed phase is excellent. Wave function optimization with the orbital transformation technique leads to good parallel performance, and outperforms traditional diagonalisation methods. Energy conserving Born-Oppenheimer dynamics can be performed, and a highly efficient scheme is obtained using an extrapolation of the d. matrix. We illustrate these findings with calcns. using commodity PCs as well as supercomputers.
- 40Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77 (18), 3865– 3868, DOI: 10.1103/PhysRevLett.77.386540https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmsVCgsbs%253D&md5=55943538406ee74f93aabdf882cd4630Generalized gradient approximation made simplePerdew, John P.; Burke, Kieron; Ernzerhof, MatthiasPhysical Review Letters (1996), 77 (18), 3865-3868CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Generalized gradient approxns. (GGA's) for the exchange-correlation energy improve upon the local spin d. (LSD) description of atoms, mols., and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental consts. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential.
- 41Giannozzi, P.; Baroni, S.; Bonini, N.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Chiarotti, G. L.; Cococcioni, M.; Dabo, I.; Dal Corso, A.; Gironcoli, S. de; Fabris, S.; Fratesi, G.; Gebauer, R.; Gerstmann, U.; Gougoussis, C.; Kokalj, A.; Lazzeri, M.; Martin-Samos, L.; Marzari, N.; Mauri, F.; Mazzarello, R.; Paolini, S.; Pasquarello, A.; Paulatto, L.; Sbraccia, C.; Scandolo, S.; Sclauzero, G.; Seitsonen, A. P.; Smogunov, A.; Umari, P.; Wentzcovitch, R. M. QUANTUM ESPRESSO: A Modular and Open-Source Software Project for Quantum Simulations of Materials. J. Phys.: Condens. Matter 2009, 21 (39), 395502, DOI: 10.1088/0953-8984/21/39/39550241https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3Mjltl2lug%253D%253D&md5=da053fa748721b6b381051a20e7a7f53QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materialsGiannozzi Paolo; Baroni Stefano; Bonini Nicola; Calandra Matteo; Car Roberto; Cavazzoni Carlo; Ceresoli Davide; Chiarotti Guido L; Cococcioni Matteo; Dabo Ismaila; Dal Corso Andrea; de Gironcoli Stefano; Fabris Stefano; Fratesi Guido; Gebauer Ralph; Gerstmann Uwe; Gougoussis Christos; Kokalj Anton; Lazzeri Michele; Martin-Samos Layla; Marzari Nicola; Mauri Francesco; Mazzarello Riccardo; Paolini Stefano; Pasquarello Alfredo; Paulatto Lorenzo; Sbraccia Carlo; Scandolo Sandro; Sclauzero Gabriele; Seitsonen Ari P; Smogunov Alexander; Umari Paolo; Wentzcovitch Renata MJournal of physics. Condensed matter : an Institute of Physics journal (2009), 21 (39), 395502 ISSN:.QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.
- 42Giannozzi, P.; Andreussi, O.; Brumme, T.; Bunau, O.; Nardelli, M. B.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Cococcioni, M.; Colonna, N.; Carnimeo, I.; Dal Corso, A.; Gironcoli, S. de; Delugas, P.; DiStasio, R. A.; Ferretti, A.; Floris, A.; Fratesi, G.; Fugallo, G.; Gebauer, R.; Gerstmann, U.; Giustino, F.; Gorni, T.; Jia, J.; Kawamura, M.; Ko, H.-Y.; Kokalj, A.; Küçükbenli, E.; Lazzeri, M.; Marsili, M.; Marzari, N.; Mauri, F.; Nguyen, N. L.; Nguyen, H.-V.; Otero-de-la-Roza, A.; Paulatto, L.; Poncé, S.; Rocca, D.; Sabatini, R.; Santra, B.; Schlipf, M.; Seitsonen, A. P.; Smogunov, A.; Timrov, I.; Thonhauser, T.; Umari, P.; Vast, N.; Wu, X.; Baroni, S. Advanced Capabilities for Materials Modelling with Quantum ESPRESSO. J. Phys.: Condens. Matter 2017, 29 (46), 465901, DOI: 10.1088/1361-648X/aa8f7942https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXntF2hsr0%253D&md5=17e46e5ac155b511f12deaeff078cc6dAdvanced capabilities for materials modelling with QUANTUM ESPRESSOGiannozzi, P.; Andreussi, O.; Brumme, T.; Bunau, O.; Buongiorno Nardelli, M.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Cococcioni, M.; Colonna, N.; Carnimeo, I.; Dal Corso, A.; de Gironcoli, S.; Delugas, P.; Di Stasio, R. A., Jr.; Ferretti, A.; Floris, A.; Fratesi, G.; Fugallo, G.; Gebauer, R.; Gerstmann, U.; Giustino, F.; Gorni, T.; Jia, J.; Kawamura, M.; Ko, H.-Y.; Kokalj, A.; Kucukbenli, E.; Lazzeri, M.; Marsili, M.; Marzari, N.; Mauri, F.; Nguyen, N. L.; Nguyen, H.-V.; Otero-de-la-Roza, A.; Paulatto, L.; Ponce, S.; Rocca, D.; Sabatini, R.; Santra, B.; Schlipf, M.; Seitsonen, A. P.; Smogunov, A.; Timrov, I.; Thonhauser, T.; Umari, P.; Vast, N.; Wu, X.; Baroni, S.Journal of Physics: Condensed Matter (2017), 29 (46), 465901/1-465901/30CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)QUANTUM ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on d.-functional theory, d.-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches. QUANTUM ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.
- 43Dal Corso, A. Pseudopotentials Periodic Table: From H to Pu. Comput. Mater. Sci. 2014, 95, 337– 350, DOI: 10.1016/j.commatsci.2014.07.04343https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtlKht7vP&md5=ca160e9de8bf835c1ffee416aed3b2e2Pseudopotentials periodic table: From H to PuDal Corso, AndreaComputational Materials Science (2014), 95 (), 337-350CODEN: CMMSEM; ISSN:0927-0256. (Elsevier B.V.)We discuss the generation of a library of projector augmented-wave (PAW) and ultrasoft pseudopotentials (PPs) for all elements of the periodic table from H to Pu. The PPs are compared with two libraries: pslibrary.0.3.1 and the GBRV library (Garrity et al., 2013). The PPs are tested on the lattice consts. of the fcc and bcc structures of the 63 elements of the GBRV library. The same parameters are used to generate fully relativistic PPs that are compared with the scalar relativistic PPs. The PPs of lanthanides and actinides are tested on all-electron data available in the literature.
- 44Taillefumier, M.; Cabaret, D.; Flank, A.-M.; Mauri, F. X-Ray Absorption near-Edge Structure Calculations with the Pseudopotentials: Application to the K Edge in Diamond and α-Quartz. Phys. Rev. B 2002, 66 (19), 195107, DOI: 10.1103/PhysRevB.66.19510744https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XptlKks7c%253D&md5=4a97196e36acdbc4f4c4747d1cb3dbdcX-ray absorption near-edge structure calculations with the pseudopotentials: Application to the K edge in diamond and α-quartzTaillefumier, Mathieu; Cabaret, Delphine; Flank, Anne-Marie; Mauri, FrancescoPhysical Review B: Condensed Matter and Materials Physics (2002), 66 (19), 195107/1-195107/8CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)The authors present a reciprocal-space pseudopotential scheme for calcg. x-ray absorption near-edge structure (XANES) spectra. The scheme incorporates a recursive method to compute absorption cross section as a continued fraction. The continued fraction formulation of absorption is advantageous in that it permits the treatment of core-hole interaction through large supercells (hundreds of atoms). The method is compared with recently developed Bethe-Salpeter approach. The method is applied to the C K edge in diamond and to the Si and O K edges in α-quartz for which polarized XANES spectra were measured. Core-hole effects are studied by varying the size of the supercell, thus leading to information similar to that obtained from cluster size anal. usually performed within multiple scattering calcns.
- 45Gougoussis, C.; Calandra, M.; Seitsonen, A. P.; Mauri, F. First-Principles Calculations of X-Ray Absorption in a Scheme Based on Ultrasoft Pseudopotentials: From α-Quartz to High-Tc Compounds. Phys. Rev. B 2009, 80 (7), 075102, DOI: 10.1103/PhysRevB.80.07510245https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFWjsb%252FM&md5=926d9d02687ec98cf51e12f59dedd77fFirst-principles calculations of x-ray absorption in a scheme based on ultrasoft pseudopotentials: From α-quartz to high-Tc compoundsGougoussis, Christos; Calandra, Matteo; Seitsonen, Ari P.; Mauri, FrancescoPhysical Review B: Condensed Matter and Materials Physics (2009), 80 (7), 075102/1-075102/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The authors develop a 1st-principles scheme based on the continued-fraction approach and ultrasoft pseudopotentials to calc. K-edge x-ray absorption spectra in solids, allowing such calcns. in transition-metal and rare-earth compds. with substantially reduced cutoffs with respect to the norm-conserving case. The authors validate the method by calcg. Si and O K edges in α-quartz, Cu K edge in Cu and in La2CuO4. For the case of Si and O edges in α-quartz and in Cu, the authors obtain good agreement with exptl. data. In the Cu K-edge spectra of La2CuO4, a material considered a real challenge for d.-functional theory, the authors attribute all the near-edge and far-edge peaks to single-particle excitations.
- 46Prendergast, D.; Galli, G. X-Ray Absorption Spectra of Water from First Principles Calculations. Phys. Rev. Lett. 2006, 96 (21), 215502, DOI: 10.1103/PhysRevLett.96.21550246https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xlt1KgtLo%253D&md5=8256bdf8d48331268d559ddcccdb2c78X-Ray Absorption Spectra of Water from First Principles CalculationsPrendergast, David; Galli, GiuliaPhysical Review Letters (2006), 96 (21), 215502/1-215502/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)We present a series of ab initio calcns. of the x-ray absorption cross section (XAS) of ice and liq. water at ambient conditions. Our results show that all available exptl. data and theor. results are consistent with the std. model of the liq. as comprising mols. with approx. four hydrogen bonds. Our simulations of ice XAS including the lowest lying excitonic state are in excellent agreement with expt. and those of a quasitetrahedral model of water are in reasonable agreement with recent measurements. Hence we propose that the std., quasitetrahedral model of water, although approx., represents a reasonably accurate description of the local structure of the liq.
- 47Nemausat, R.; Gervais, C.; Brouder, C.; Trcera, N.; Bordage, A.; Coelho-Diogo, C.; Florian, P.; Rakhmatullin, A.; Errea, I.; Paulatto, L.; Lazzeri, M.; Cabaret, D. Temperature Dependence of X-Ray Absorption and Nuclear Magnetic Resonance Spectra: Probing Quantum Vibrations of Light Elements in Oxides. Phys. Chem. Chem. Phys. 2017, 19 (8), 6246– 6256, DOI: 10.1039/C6CP08393E47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsleitbY%253D&md5=d911560ed801dc9573877f6b35b1de65Temperature dependence of X-ray absorption and nuclear magnetic resonance spectra: probing quantum vibrations of light elements in oxidesNemausat, Ruidy; Gervais, Christel; Brouder, Christian; Trcera, Nicolas; Bordage, Amelie; Coelho-Diogo, Cristina; Florian, Pierre; Rakhmatullin, Aydar; Errea, Ion; Paulatto, Lorenzo; Lazzeri, Michele; Cabaret, DelphinePhysical Chemistry Chemical Physics (2017), 19 (8), 6246-6256CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)A combined exptl.-theor. study on the temp. dependence of the x-ray absorption near-edge structure (XANES) and NMR spectra of periclase (MgO), spinel (MgAl2O4), corundum (α-Al2O3), berlinite (α-AlPO4), stishovite and α-quartz (SiO2) is reported. Predictive calcns. are presented when exptl. data are not available. For these light-element oxides, both exptl. techniques detect systematic effects related to quantum thermal vibrations which are well reproduced by d.-functional theory simulations. In calcns., thermal fluctuations of the nuclei are included by considering nonequil. configurations according to finite-temp. quantum statistics at the quasiharmonic level. The influence of nuclear quantum fluctuations on XANES and NMR spectroscopies is particularly sensitive to the coordination no. of the probed cation. Also, the relative importance of nuclear dynamics and thermal expansion is quantified over a large range of temps.
- 48Rehr, J. J.; Albers, R. C. Theoretical Approaches to X-Ray Absorption Fine Structure. Rev. Mod. Phys. 2000, 72 (3), 621– 654, DOI: 10.1103/RevModPhys.72.62148https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXmtVOqtrg%253D&md5=5fb478a8ff6028b7ba5681921050fca7Theoretical approaches to x-ray absorption fine structureRehr, J. J.; Albers, R. C.Reviews of Modern Physics (2000), 72 (3), 621-654CODEN: RMPHAT; ISSN:0034-6861. (American Physical Society)Dramatic advances in the understanding of x-ray absorption fine structure (XAFS) were made over the past few decades, which led ultimately to a highly quant. theory. This review with many refs. covers these developments from a unified multiple-scattering viewpoint. The authors focus on extended x-ray absorption fine structure (EXAFS) well above an x-ray edge, and, to a lesser extent, on x-ray absorption near-edge structure (XANES) closer to an edge. The discussion includes both formal considerations, derived from a many-electron formulation, and practical computational methods based on independent-electron models, with many-body effects lumped into various inelastic losses and energy shifts. The main conceptual issues in XAFS theory are identified and their relative importance is assessed; these include the convergence of the multiple-scattering expansion, curved-wave effects, the scattering potential, inelastic losses, self-energy shifts, and vibrations and structural disorder. The advantages and limitations of current computational approaches are addressed, with particular regard to quant. exptl. comparisons.
- 49Teo, B. K. EXAFS: Basic Principles and Data Analysis; Springer Science & Business Media, 2012.There is no corresponding record for this reference.
- 50Glazer, A. M. Simple Ways of Determining Perovskite Structures. Acta Crystallogr., Sect. A: Found. Crystallogr. 1975, 31 (6), 756– 762, DOI: 10.1107/S0567739475001635There is no corresponding record for this reference.
- 51Worhatch, R. J.; Kim, H.; Swainson, I. P.; Yonkeu, A. L.; Billinge, S. J. L. Study of Local Structure in Selected Organic–Inorganic Perovskites in the Pm3̅m Phase. Chem. Mater. 2008, 20 (4), 1272– 1277, DOI: 10.1021/cm702668d51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXps1Krsw%253D%253D&md5=83b85b82b8d8a8d1edbc51320f8a074fStudy of Local Structure in Selected Organic-Inorganic Perovskites in the Pm‾3m PhaseWorhatch, Richard J.; Kim, HyunJeong; Swainson, Ian P.; Yonkeu, Andre L.; Billinge, Simon J. L.Chemistry of Materials (2008), 20 (4), 1272-1277CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The local structures of the inorg. component of selected org.-inorg. perovskites (OIPs) were studied by analyzing the x-ray pair distribution function. Whereas the long-range structure of each perovskite is the untilted Pm3‾m phase, all the OIPs showed significant internal distortion of the octahedra. Varying the halide has a significant impact on the lattice const. There is evidence of local lone-pair distortions for certain compns. The most complex case of disorder appears to be that of CH3NH3SnBr3.
- 52Carignano, M. A.; Aravindh, S. A.; Roqan, I. S.; Even, J.; Katan, C. Critical Fluctuations and Anharmonicity in Lead Iodide Perovskites from Molecular Dynamics Supercell Simulations. J. Phys. Chem. C 2017, 121 (38), 20729– 20738, DOI: 10.1021/acs.jpcc.7b0822052https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsVeksrbJ&md5=2e6d110e2e834828571e32954a4354ecCritical Fluctuations and Anharmonicity in Lead Iodide Perovskites from Molecular Dynamics Supercell SimulationsCarignano, Marcelo A.; Aravindh, S. Assa; Roqan, Iman S.; Even, Jacky; Katan, ClaudineJournal of Physical Chemistry C (2017), 121 (38), 20729-20738CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The authors present a systematic study based on 1st-principles mol. dynamics simulations of lead iodide perovskites with 3 different cations, including methylammonium (MA), formamidinium (FA), and Cs. Using the high-temp. perovskite structure as a ref., the authors study the instabilities that develop as the material is cooled down to 370 K. All 3 perovskites display anharmonicity in the motion of the I atoms, with the stronger effect obsd. for the MAPbI3 and CsPbI3. At high temp., this behavior can be traced back to the reduced effective size of the Cs+ and MA+ cations. MAPbI3 undergoes a spontaneous phase transition within the simulation model driven by the dipolar interaction between neighboring MA cations as the temp. is decreased from 450 K. The reverse transformation from tetragonal to cubic is also monitored through the large distribution of the octahedral tilting angles accompanied by an increase in the anharmonicity of the I atom motion. Both MA and FA hybrid perovskites show a strong coupling between the mol. orientations and the local lattice deformations, suggesting mixed order-disorder/displacive characters of the high-temp. phase transitions.
- 53Prasanna, R.; Gold-Parker, A.; Leijtens, T.; Conings, B.; Babayigit, A.; Boyen, H.-G.; Toney, M. F.; McGehee, M. D. Band Gap Tuning via Lattice Contraction and Octahedral Tilting in Perovskite Materials for Photovoltaics. J. Am. Chem. Soc. 2017, 139 (32), 11117– 11124, DOI: 10.1021/jacs.7b0498153https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFKkurrM&md5=849c6ff83b9086c4abc02ee59256fb21Band Gap Tuning via Lattice Contraction and Octahedral Tilting in Perovskite Materials for PhotovoltaicsPrasanna, Rohit; Gold-Parker, Aryeh; Leijtens, Tomas; Conings, Bert; Babayigit, Aslihan; Boyen, Hans-Gerd; Toney, Michael F.; McGehee, Michael D.Journal of the American Chemical Society (2017), 139 (32), 11117-11124CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Tin and lead iodide perovskite semiconductors of the compn. AMX3, where M is a metal and X is a halide, are leading candidates for high efficiency low cost tandem photovoltaics, in part because they have band gaps that can be tuned over a wide range by compositional substitution. We exptl. identify two competing mechanisms through which the A-site cation influences the band gap of 3D metal halide perovskites. Using a smaller A-site cation can distort the perovskite lattice in two distinct ways: by tilting the MX6 octahedra or by simply contracting the lattice isotropically. The former effect tends to raise the band gap, while the latter tends to decrease it. Lead iodide perovskites show an increase in band gap upon partial substitution of the larger formamidinium with the smaller cesium, due to octahedral tilting. Perovskites based on tin, which is slightly smaller than lead, show the opposite trend: they show no octahedral tilting upon Cs-substitution but only a contraction of the lattice, leading to progressive redn. of the band gap. We outline a strategy to systematically tune the band gap and valence and conduction band positions of metal halide perovskites through control of the cation compn. Using this strategy, we demonstrate solar cells that harvest light in the IR up to 1040 nm, reaching a stabilized power conversion efficiency of 17.8%, showing promise for improvements of the bottom cell of all-perovskite tandem solar cells. The mechanisms of cation-based band gap tuning we describe are broadly applicable to 3D metal halide perovskites and will be useful in further development of perovskite semiconductors for optoelectronic applications.
- 54Lanigan-Atkins, T.; He, X.; Krogstad, M. J.; Pajerowski, D. M.; Abernathy, D. L.; Xu, G. N. M. N.; Xu, Z.; Chung, D.-Y.; Kanatzidis, M. G.; Rosenkranz, S.; Osborn, R.; Delaire, O. Two-Dimensional Overdamped Fluctuations of the Soft Perovskite Lattice in CsPbBr3. Nat. Mater. 2021, 20 (7), 977– 983, DOI: 10.1038/s41563-021-00947-y54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXmsF2ju7c%253D&md5=a57c2279298f7fedbfc0bee62602ce89Two-dimensional overdamped fluctuations of the soft perovskite lattice in CsPbBr3Lanigan-Atkins, T.; He, X.; Krogstad, M. J.; Pajerowski, D. M.; Abernathy, D. L.; Xu, Guangyong N. M. N.; Xu, Zhijun; Chung, D.-Y.; Kanatzidis, M. G.; Rosenkranz, S.; Osborn, R.; Delaire, O.Nature Materials (2021), 20 (7), 977-983CODEN: NMAACR; ISSN:1476-1122. (Nature Portfolio)Lead halide perovskites exhibit structural instabilities and large at. fluctuations thought to impact their optical and thermal properties, yet detailed structural and temporal correlations of their at. motions remain poorly understood. Here, these correlations are resolved in CsPbBr3 crystals using momentum-resolved neutron and X-ray scattering measurements as a function of temp., complemented with first-principles simulations. We uncover a striking network of diffuse scattering rods, arising from the liq.-like damping of low-energy Br-dominated phonons, reproduced in our simulations of the anharmonic phonon self-energy. These overdamped modes cover a continuum of wave vectors along the edges of the cubic Brillouin zone, corresponding to two-dimensional sheets of correlated rotations in real space, and could represent precursors to proposed two-dimensional polarons. Further, these motions directly impact the electronic gap edge states, linking soft anharmonic lattice dynamics and optoelectronic properties. These results provide insights into the highly unusual at. dynamics of halide perovskites, relevant to further optimization of their optical and thermal properties.
- 55Wiktor, J.; Rothlisberger, U.; Pasquarello, A. Predictive Determination of Band Gaps of Inorganic Halide Perovskites. J. Phys. Chem. Lett. 2017, 8 (22), 5507– 5512, DOI: 10.1021/acs.jpclett.7b0264855https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslags7%252FO&md5=512e8efb5884cde66ed5919664952eadPredictive Determination of Band Gaps of Inorganic Halide PerovskitesWiktor, Julia; Rothlisberger, Ursula; Pasquarello, AlfredoJournal of Physical Chemistry Letters (2017), 8 (22), 5507-5512CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)We carry out first-principles calcns. of band gaps of cubic inorg. perovskites belonging to the class CsBX3, with B = Pb, Sn and X = Cl, Br, I. We use the quasi-particle self-consistent GW method with efficient vertex corrections to calc. the electronic structure of the studied materials. We demonstrate the importance of including the higher-lying core and semicore shells among the valence states. For a meaningful comparison with exptl. values, we account for thermal vibrations and disorder through ab initio mol. dynamics. Addnl., we calc. the spin-orbit coupling at levels of theory of increasing accuracy and show that semilocal d. functionals significantly underestimate these corrections. We show that all of these effects need to be properly included in order to obtain reliable predictions for the band gaps of halide perovskites.
- 56Bruce, A. D.; Cowley, R. A. Structural Phase Transitions; Monographs on physics; Taylor & Francis: London, 1981.There is no corresponding record for this reference.
- 57Shirane, G. Neutron Scattering Studies of Structural Phase Transitions at Brookhaven. Rev. Mod. Phys. 1974, 46 (3), 437– 449, DOI: 10.1103/RevModPhys.46.43757https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2cXlt1Olsbo%253D&md5=6a8670e726292af013cdba3ec5111e96Neutron scattering studies of structural phase transitions at BrookhavenShirane, G.Reviews of Modern Physics (1974), 46 (3), 437-49CODEN: RMPHAT; ISSN:0034-6861.A review of systematic neturon scattering studies on phase transitions carried out at Brookhaven is given with 57 refs.
- 58Dove, M. T. Introduction to Lattice Dynamics; Cambridge University Press: Cambridge, 1993.There is no corresponding record for this reference.
- 59Rodová, M.; Brožek, J.; Knížek, K.; Nitsch, K. Phase Transitions in Ternary Caesium Lead Bromide. J. Therm. Anal. Calorim. 2003, 71 (2), 667– 673, DOI: 10.1023/A:102283680082059https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXitVynsbs%253D&md5=1f443a54159b2217749ed085191a2796Phase transitions in ternary cesium lead bromideRodova, M.; Brozek, J.; Knizek, K.; Nitsch, K.Journal of Thermal Analysis and Calorimetry (2003), 71 (2), 667-673CODEN: JTACF7; ISSN:1388-6150. (Kluwer Academic Publishers)Phase transitions in CsPbBr3 were studied by DSC, TMA and high temp. x-ray diffraction. The samples were prepd. from soln. by H2O evapn. and from the melt. On the DSC curves as well as on the temp. dependence of the lattice consts. of CsPbBr3 only two effects were found belonging to the earlier published phase transitions at 88 and 130° and no further effects. Linear thermal expansion coeffs. α of individual CsPbBr3 modifications were calcd. from both TMA and high temp. x-ray diffraction. The structural parameters of the room temp. orthorhombic phase were refined. CsPbBr3 prepd. from the soln. contained ∼10% of CsPb2Br5 and so the DSC curve of pure CsPb2Br5 was also measured and an effect at a temp. of 68.5° was found.
- 60Nemausat, R.; Cabaret, D.; Gervais, C.; Brouder, C.; Trcera, N.; Bordage, A.; Errea, I.; Mauri, F. Phonon Effects on X-Ray Absorption and Nuclear Magnetic Resonance Spectroscopies. Phys. Rev. B 2015, 92 (14), 144310, DOI: 10.1103/PhysRevB.92.14431060https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktVKjsLc%253D&md5=8febac528fd70e67a5ff8bef51da3471Phonon effects on X-ray absorption and nuclear magnetic resonance spectroscopiesNemausat, Ruidy; Cabaret, Delphine; Gervais, Christel; Brouder, Christian; Trcera, Nicolas; Bordage, Amelie; Errea, Ion; Mauri, FrancescoPhysical Review B: Condensed Matter and Materials Physics (2015), 92 (14), 144310/1-144310/12CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)In material sciences, spectroscopic approaches combining ab initio calcns. with expts. are commonly used to accurately analyze the exptl. spectral data. Most state-of-the-art first-principles calcns. are usually performed assuming an equil. static lattice. Yet, nuclear motion affects spectra even when reduced to the zero-point motion at 0 K. We propose a framework based on d.-functional theory that includes quantum thermal fluctuations in theor. x-ray absorption near-edge structure (XANES) and solid-state NMR (NMR) spectroscopies and allows to well describe temp. effects obsd. exptl. Within the Born-Oppenheimer and quasiharmonic approxns., we incorporate the nuclear motion by generating several nonequil. configurations from the dynamical matrix. The averaged calcd. XANES and NMR spectral data have been compared to expts. in MgO. The good agreement obtained between expts. and calcns. validates the developed approach, which suggests that calcg. the XANES spectra at finite temp. by averaging individual nonequil. configurations is a suitable approxn. This study highlights the relevance of phonon renormalization and the relative contributions of thermal expansion and nuclear dynamics on NMR and XANES spectra on a wide range of temps.
- 61Swainson, I. P.; Stock, C.; Parker, S. F.; Van Eijck, L.; Russina, M.; Taylor, J. W. From Soft Harmonic Phonons to Fast Relaxational Dynamics in CH3NH3PbBr3. Phys. Rev. B 2015, 92 (10), 100303, DOI: 10.1103/PhysRevB.92.10030361https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjtVyhsL8%253D&md5=1be5add9e7055f0b2a3e9337e0038d40From soft harmonic phonons to fast relaxational dynamics in CH3NH3PbBr3Swainson, I. P.; Stock, C.; Parker, S. F.; Van Eijck, L.; Russina, M.; Taylor, J. W.Physical Review B: Condensed Matter and Materials Physics (2015), 92 (10), 100303/1-100303/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The lead-halide perovskites, including CH3NH3PbBr3, are components in cost effective, highly efficient photovoltaics, where the interactions of the mol. cations with the inorg. framework are suggested to influence the electronic and ferroelec. properties. CH3NH3PbBr3 undergoes a series of structural transitions assocd. with orientational order of the CH3NH3 (methylammonium) mol. cation and tilting of the PbBr3 host framework. We apply high-resoln. neutron scattering to study the soft harmonic phonons assocd. with these transitions, and find a strong coupling between the PbBr3 framework and the quasistatic CH3NH3 dynamics at low energy transfers. At higher energy transfers, we observe a PbBr6 octahedra soft mode driving a transition at 150 K from bound mol. excitations at low temps. to relatively fast relaxational excitations that extend up to ∼50-100 meV. We suggest that these temporally overdamped dynamics enables possible indirect band gap processes in these materials that are related to the enhanced photovoltaic properties.
Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpclett.2c00281.
(1) Samples and characterization, (2) CsPbBr3 model crystal structures and XRD, (3) T-dependent XRD and XANES data analysis, (4) MD computational methods, (5) XANES computational methods, (6) volume expansion contribution to T-dependent XANES changes, (7) time evolution of Pb–Br–Pb angle distribution in MD simulations, (8) thermal displacements of Cs, Pb, and Br sites in MD simulations (PDF)
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