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Title: Origin of Pronounced Nonlinear Band Gap Behavior in Lead–Tin Hybrid Perovskite Alloys

Mixed lead-tin hybrid perovskite alloy CH 3NH 3(Pb 1-xSn x)I 3 attracted significant attention lately because of the reduction of its band gap below both end compounds, which makes it a promising bottom cell material in all-perovskite tandem solar cells. The effect is a consequence of a strongly nonlinear dependence of the alloy band gap on chemical composition. Here, we use electronic structure calculations at different levels of theory (density functional theory (DFT), hybrid DFT, and QSGW, with and without spin-orbit interactions) to investigate the presently elusive origin of this effect. Contrary to current conflicting studies, our results show that neither spin-orbit interactions nor the composition induced changes of the crystal structure and ordering of atoms contributes to the nonlinearity of the band gap. We find that the strong nonlinearity is primarily a consequence of chemical effects, i.e., the mismatch in energy between s and p atomic orbitals of Pb and Sn, which form the band edges of the alloy. These results unravel the nature of the band gap bowing in Sn/Pb hybrid perovskite alloys and offer a relatively simple way to estimate evolution of the band gap in other hybrid perovskite alloys.
Authors:
ORCiD logo [1] ;  [2] ;  [2] ;  [3] ;  [2] ;  [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States); Colorado School of Mines, Golden, CO (United States)
  2. King's College London (United Kingdom)
  3. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Report Number(s):
NREL/JA-5K00-72043
Journal ID: ISSN 0897-4756
Grant/Contract Number:
AC36-08GO28308
Type:
Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 30; Journal Issue: 11; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; perovskites; alloys; electronic structure; band gap
OSTI Identifier:
1462334

Goyal, Anuj, McKechnie, Scott, Pashov, Dimitar, Tumas, William, Schilfgaarde, Mark van, and Stevanović, Vladan. Origin of Pronounced Nonlinear Band Gap Behavior in Lead–Tin Hybrid Perovskite Alloys. United States: N. p., Web. doi:10.1021/acs.chemmater.8b01695.
Goyal, Anuj, McKechnie, Scott, Pashov, Dimitar, Tumas, William, Schilfgaarde, Mark van, & Stevanović, Vladan. Origin of Pronounced Nonlinear Band Gap Behavior in Lead–Tin Hybrid Perovskite Alloys. United States. doi:10.1021/acs.chemmater.8b01695.
Goyal, Anuj, McKechnie, Scott, Pashov, Dimitar, Tumas, William, Schilfgaarde, Mark van, and Stevanović, Vladan. 2018. "Origin of Pronounced Nonlinear Band Gap Behavior in Lead–Tin Hybrid Perovskite Alloys". United States. doi:10.1021/acs.chemmater.8b01695.
@article{osti_1462334,
title = {Origin of Pronounced Nonlinear Band Gap Behavior in Lead–Tin Hybrid Perovskite Alloys},
author = {Goyal, Anuj and McKechnie, Scott and Pashov, Dimitar and Tumas, William and Schilfgaarde, Mark van and Stevanović, Vladan},
abstractNote = {Mixed lead-tin hybrid perovskite alloy CH3NH3(Pb1-xSnx)I3 attracted significant attention lately because of the reduction of its band gap below both end compounds, which makes it a promising bottom cell material in all-perovskite tandem solar cells. The effect is a consequence of a strongly nonlinear dependence of the alloy band gap on chemical composition. Here, we use electronic structure calculations at different levels of theory (density functional theory (DFT), hybrid DFT, and QSGW, with and without spin-orbit interactions) to investigate the presently elusive origin of this effect. Contrary to current conflicting studies, our results show that neither spin-orbit interactions nor the composition induced changes of the crystal structure and ordering of atoms contributes to the nonlinearity of the band gap. We find that the strong nonlinearity is primarily a consequence of chemical effects, i.e., the mismatch in energy between s and p atomic orbitals of Pb and Sn, which form the band edges of the alloy. These results unravel the nature of the band gap bowing in Sn/Pb hybrid perovskite alloys and offer a relatively simple way to estimate evolution of the band gap in other hybrid perovskite alloys.},
doi = {10.1021/acs.chemmater.8b01695},
journal = {Chemistry of Materials},
number = 11,
volume = 30,
place = {United States},
year = {2018},
month = {5}
}