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Title: Polaron Stabilization by Cooperative Lattice Distortion and Cation Rotations in Hybrid Perovskite Materials

Solution-processed organometallic perovskites have rapidly developed into a top candidate for the active layer of photovoltaic devices. In spite of the remarkable progress associated with perovskite materials, many questions about the fundamental photophysical processes taking place in these devices, remain open. High on the list of unexplained phenomena are very modest mobilities despite low charge carrier effective masses. Moreover, experiments elucidate unique degradation of photocurrent affecting stable operation of perovskite solar cells. These puzzles suggest that, while ionic hybrid perovskite devices may have efficiencies on par with conventional Si and GaAs devices, they exhibit more complicated charge transport phenomena. We report the results from an in-depth computational study of small polaron formation, electronic structure, charge density, and reorganization energies using both periodic boundary conditions and isolated structures. Using the hybrid density functional theory, we found that volumetric strain in a CsPbI 3 cluster creates a polaron with binding energy of around 300 and 900 meV for holes and electrons, respectively. In the MAPbI 3 (MA = CH 3NH 3) cluster, both volumetric strain and MA reorientation effects lead to larger binding energies at around 600 and 1300 meV for holes and electrons, respectively. Such large reorganization energies suggest appearance ofmore » small polarons in organometallic perovskite materials. Furthermore, the fact that both volumetric lattice strain and MA molecular rotational degrees of freedom can cooperate to create and stabilize polarons indicates that in order to mitigate this problem, formamidinium (FA = HC(NH 2) 2) and cesium (Cs) based crystals and alloys, are potentially better materials for solar cell and other optoelectronic applications.« less
Authors:
ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [3] ;  [4] ; ORCiD logo [2] ;  [4] ;  [5] ;  [6] ;  [6] ; ORCiD logo [3] ;  [2] ; ORCiD logo [2] ; ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Physics adn Chemistry of Materials
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Physics and Application
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Physical Chemistry and Applied Spectroscopy
  4. Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials
  5. Univ. of Rennes (France). Inst. of Chemical Sciences
  6. National Center for Scientific Research (CNRS), Rennes (France). Optical Functions for Information Technology
Publication Date:
Report Number(s):
BNL-112594-2016-JA; LA-UR-16-21882
Journal ID: ISSN 1530-6984; R&D Project: 16063; 16058; KC0403020
Grant/Contract Number:
SC00112704; AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 16; Journal Issue: 6; Journal ID: ISSN 1530-6984
Publisher:
American Chemical Society
Research Org:
Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; cation rotations; Organic and #8722; inorganic perovskite; photovoltaic; polaron; Center for Functional Nanomaterials; Energy Sciences; Inorganic and Physical Chemistry; Material Science; organic-inorganic perovskite
OSTI Identifier:
1336128
Alternate Identifier(s):
OSTI ID: 1357115