Polaron Stabilization by Cooperative Lattice Distortion and Cation Rotations in Hybrid Perovskite Materials
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Physics adn Chemistry of Materials
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Physics and Application
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Physical Chemistry and Applied Spectroscopy
- Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials
- Univ. of Rennes (France). Inst. of Chemical Sciences
- National Center for Scientific Research (CNRS), Rennes (France). Optical Functions for Information Technology
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 CsPbI3 cluster creates a polaron with binding energy of around 300 and 900 meV for holes and electrons, respectively. In the MAPbI3 (MA = CH3NH3) 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 of 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(NH2)2) and cesium (Cs) based crystals and alloys, are potentially better materials for solar cell and other optoelectronic applications.
- Research Organization:
- Brookhaven National Laboratory (BNL), Upton, NY (United States). Center for Functional Nanomaterials; Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
- Grant/Contract Number:
- AC52-06NA25396
- OSTI ID:
- 1336128
- Alternate ID(s):
- OSTI ID: 1357115
- Report Number(s):
- BNL--112594-2016-JA; LA-UR--16-21882; KC0403020
- Journal Information:
- Nano Letters, Journal Name: Nano Letters Journal Issue: 6 Vol. 16; ISSN 1530-6984
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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