Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session D43: Theory of Novel Phenomena in Halide PerovskitesInvited Live Streamed
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Sponsoring Units: DCOMP Chair: John Lyons, United States Naval Research Laboratory Room: McCormick Place W-375B |
Monday, March 14, 2022 3:00PM - 3:36PM |
D43.00001: Chirality transfer, inversion symmetry breaking and spin-splitting in layered perovskites Invited Speaker: Volker Blum The strongly spin-orbit coupled conduction bands of layered (so-called two-dimensional) organic-inorganic lead halide perovskites can show large spin splittings, suggesting the possibility of spin-selective transport and future spintronic applications. We here use high-precision, all-electron first-principles theory (FHI-aims code [1,2]) to show how chiral organic components, structural transfer of chirality, inversion asymmetry and spin splitting and spin texture in layered perovskites are quantitatively linked [3,4]. Crystalline layered perovskites can be synthesized as high-quality single crystals, leading to unit cell sizes of hundreds of atoms (over 1,000 atoms in simulations that include defects). We computationally address their structure and electronic properties by dispersion-corrected semilocal and hybrid DFT and an efficient treatment of spin-orbit coupling, benchmarked against a fully relativistic, quasi-four-component electronic structure method [5]. Our approach faithfully predicts the quantum-well character of complex layered perovskites. We then show how introducing a particular chiral molecule can distort the inorganic structure so as to create strong spin splitting in the conduction bands of the quantum well [3]. Based on a group of chiral organic-inorganic crystalline layered perovskites, we finally show that a particular bond angle difference in the structure can serve as a faithful predictor of conduction band spin splitting in this promising class of semiconductor materials [4]. |
Monday, March 14, 2022 3:36PM - 4:12PM |
D43.00002: Sources of nonradiative recombination in halide perovskites Invited Speaker: Xie Zhang While halide perovskites exhibit great promise in highly efficient solar cells and light emitters, their bottleneck of nonradiative losses has become increasingly apparent. To further enhance their optoelectronic performance, identifying the sources of nonradiative recombination is key. Despite the fact that nonradiative recombination rates can be experimentally measured, it is challenging to determine the microscopic nature of the nonradiative sources. In recent years, we have developed first-principles approaches that allow us to quantitatively compute the defect-assisted nonradiative recombination [1] and Auger recombination [2] rates, and to rigorously identify the nature of the nonradiative losses. By applying our methodology to halide perovskites, we have identified a number of important defects that mediate nonradiative recombination, including intrinsic defects such as iodine interstitials [3,4] and hydrogen vacancies [5], and extrinsic defects such as bismuth impurities [6]. We show that the commonly used methylammonium cation does not suppress nonradiative recombination, but in fact gives rise to the formation of hydrogen vacancies. We have also demonstrated the origin of the unexpectedly strong Auger recombination in halide perovskites [7,8]. These important insights will guide further optimization of perovskite solar cells toward enhanced performance. |
Monday, March 14, 2022 4:12PM - 4:48PM |
D43.00003: Recent results on metal halide perovskites and their interfaces Invited Speaker: Claudine KATAN The considerable attention paid to metal halide perovskites (MHP) in recent years led to several scientific and technological advances. This in turn raised important questions that currently challenge the limits of available theoretical techniques and atomistic models. At present, perovskite materials are mixed with each other in complex alloys and heterostructures, including 2D/3D compositions, combined with additives or protecting layers to improve their stability and/or defectiveness as well as assembled with carrier selective layers, other materials and components to turn them into devices. Considering the target applications, ambient conditions predominate with additional issues related, for example, to the intrinsic dynamics in action in the MHP structure that may not be well captured using static averaged structures. |
Monday, March 14, 2022 4:48PM - 5:24PM |
D43.00004: Carrier localization in halide perovskites Invited Speaker: Julia Wiktor Metal halide perovskites have attracted remarkable interest as promising materials for optoelectronic applications. One of the characteristics underpinning their performance is the nature of the photogenerated excess charges. Compounds from the family of halide perovskites are generally easily polarizable, which leads to strong charge-lattice interactions, and formation of polarons. I will discuss different types of polaronic states that have been predicted computationally in lead and tin based halide perovskites and how they can affect the properties of these materials. From a modeling perspective, I will also show how various effects, such as self-interaction, spin-orbit coupling and temperature affect the computed properties of the polaronic states. |
Monday, March 14, 2022 5:24PM - 6:00PM |
D43.00005: Segregation and stabilization of lead halide perovskites Invited Speaker: Shuxia Tao Mixed halide perovskites that are thermodynamically stable in the dark demix under illumination. This is problematic for their application in solar cells. We present a unified thermodynamic theory for this light-induced halide segregation that is based on a free energy lowering of photocarriers funnelling to a nucleated phase with different halide composition and lower band gap than the parent phase. We apply the theory to a sequence of mixed 3D iodine-bromine perovskites. The spinodals separating metastable and unstable regions in the composition-temperature phase diagrams only slightly change under illumination, while light-induced binodals separating stable and metastable regions appear signalling the nucleation of a low-band gap iodine-rich phase. We find that the threshold photocarrier density for halide segregation is governed by the band gap difference of the parent and iodine-rich phase. Partial replacement of organic cations by cesium reduces this difference and therefore has a stabilizing effect. Combining this theory with kinetic investigations, we show expanding from 3D to 2D systems, the photo-induced problems can also be suppressed. The study points out also important handles for materials design for stable halide perovskites. |
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