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Metal Halide Perovskites (MHPs) took the scientific and engineering world by a storm, due to their unique defect tolerance, giving rise to a rapid development of various applications, including solar cells, detectors and quantum information media. Applications of MHPs are rooted in their highly unusual physical and chemical properties, combining features of inorganic, organic and liquid media. The inorganic component of MHPs ensures efficient charge transport. The organic components protect against exposure to moisture and oxygen, and enable formation of 3D, 2D and 1D structures. Similarly to liquids, MHPs screen charges very well, forming large polarons, akin to solvation, and reducing charge recombination. By performing atomistic quantum dynamics simulations, we uncovered many peculiar phenomena, which are apparently unique to these rather unusual materials.
MHPs are much softer than typical inorganic semiconductors. They are strongly anharmonic, undergo large-scale slow motions, and respond strongly to external perturbations. Local disorder plays a very important role in charge carrier dynamics in MHPs.
D. Strandell, Y. F. Wu, C. Mora-Perez, O. Prezhdo, P. Kambhampati, “Breaking the Condon Approximation for Light Emission from Metal Halide Perovskite Nanocrystals”, J. Phys. Chem. Lett., 14, 11281-11285 (2023).
L. Qiao, W. H. Fang, R. Long, O. V. Prezhdo, “Elimination of Charge Recombination Centers in Metal Halide Perovskites by Strain”, J. Am. Chem. Soc., 143, 9982-9990 (2021).
W. B. Chu, W. A. Saidi, J. Zhao, O. V. Prezhdo, “Soft Lattice and Defect Covalency Rationalize Tolerance of β‐CsPbI3 Perovskite Solar Cells to Native Defects”, Angew. Chem. Int. Ed., 59, 6435-6441 (2020).
Local disorder plays a very important role in charge carrier dynamics in MHPs. It helps to maintain long carrier lifetimes at high temperatures and facilitates exciton dissociation.
R. Shi, R. Long, W. H. Fang, O. V. Prezhdo, “Rapid Interlayer Charge Separation and Extended Carrier Lifetimes due to Spontaneous Symmetry Breaking in Organic and Mixed Organic–Inorganic Dion–Jacobson Perovskites”, J. Am. Chem. Soc., 145, 5297-5309 (2023).
Z. S. Zhang, W. H. Fang, R. Long, O. V. Prezhdo, “Exciton dissociation and suppressed charge recombination at 2D perovskite edges: key roles of unsaturated halide bonds and thermal disorder”, J. Am. Chem. Soc., 141, 15557-15566 (2019).
W. Li, J. F. Tang, D. Casanova, O. V. Prezhdo, “Time-domain ab initio analysis rationalizes the unusual temperature dependence of charge carrier relaxation in lead halide perovskite”, ACS Energ. Lett., 3, 2713–2720 (2018).
Energies of defect levels in MHPs fluctuate very significantly. Defects that are deep at low temperature can become shallow at a finite temperature and vice versa. Thus, the standard classification of defects into shallow or deep does not quite work in this case.
B. P. Wang, W. B. Chu, Y. F. Wu, D. Casanova, W. A. Saidi, O. V. Prezhdo, “Electron-Volt Fluctuation of Defect Levels in Metal Halide Perovskites on a 100 Ps Time Scale”, J. Phys. Chem. Lett., 13, 5946-5952 (2022).
D. Y. Liu, Y. F. Wu, A. S. Vasenko, O. V. Prezhdo, “Grain Boundary Sliding and Distortion on a Nanosecond Timescale Induce Trap States in CsPbBr3: Ab Initio Investigation with Machine Learning Force Field”, Nanoscale, 15, 285-293 (2022)
MHPs exhibit a very broad range of time and length scales. There is a significant synergy between motions of electrons, ions, and local and extended defects.
C. J. Tong, X. Y. Cai, A. Y. Zhu, L. M. Liu, O. V. Prezhdo, “How Hole Injection Accelerates Both Ion Migration and Nonradiative Recombination in Metal Halide Perovskites”, J. Am. Chem. Soc., 144, 6604-6612 (2022).
W. Li, Y. Y. Sun, L. Q. Li, Z. H. Zhou, J. F. Tang, O. V. Prezhdo, “Control of charge recombination in perovskites by oxidation state of halide vacancy”, J. Am. Chem. Soc., 140, 15753-15763 (2018).
Highly excited “hot” carriers can remain hot for significant amounts of time in MHPs, enhancing charge transport.
T. Wang, J. Hidalgo, W. Chu, L. Jin, J. M. Snaider, S. Deng, T. Zhu, O. Prezhdo, J.-P. Correa Baena, L. Huang, “Protecting Hot Carriers by Tuning Hybrid Perovskite Structures with Alkali Cations”, Sci. Adv., 6, eabb1336 (2020).
Charges are efficiently screened in MHP bulk. In contrast, confinement of charges in MHP quantum dots strongly enhance their interactions, making MHP quantum dots into efficient light emitters and creating opportunities for Auger-type processes.
D. Strandell, C. Mora-Perez, Y. F. Wu, O. V. Prezhdo, P. Kambhampati, “Excitonic Quantum Coherence in Light Emission from CsPbBr3 Metal-Halide Perovskite Nanocrystals”, Nano Lett., 24, 61-66 (2023).
H. Baker, C. Mora-Perez, C. Sonnichsen, D. Strandell, O. V. Prezhdo, P. Kambhampati, “Breaking Phonon Bottlenecks through Efficient Auger Processes in Perovskite Nanocrystals”, ACS Nano, 17, 3913-3920 (2023).
Although the inorganic lattice that supports charges in MHPs is composed of heavy elements, such as Pb and I, and the organic component has no contribution to the charge wavefunctions, nuclear quantum effects from the light H atoms of the organic part have a significant influence on MHP properties even at ambient and increased temperatures.
Y. Liu, R. Long, W. H. Fang, O. V. Prezhdo, “Nuclear Quantum Effects Prolong Charge Carrier Lifetimes in Hybrid Organic–Inorganic Perovskites”, J. Am. Chem. Soc., 145, 14112–14123 (2023).
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