Origin of Pronounced Nonlinear Band Gap Behavior in Lead-Tin Hybrid Perovskite Alloys

Anuj Goyal, William Tumas, Vladan Stevanovic, Scott McKechnie, Dimitar Pashov, Mark Schilfgaarde

Research output: Contribution to journalArticlepeer-review

161 Scopus Citations

Abstract

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.

Original languageAmerican English
Pages (from-to)3920-3928
Number of pages9
JournalChemistry of Materials
Volume30
Issue number11
DOIs
StatePublished - 2018

Bibliographical note

Publisher Copyright:
Copyright © 2018 American Chemical Society.

NREL Publication Number

  • NREL/JA-5K00-72043

Keywords

  • alloys
  • band gap
  • electronic structure
  • perovskites

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