Parity-Forbidden Transitions and Their Impact on the Optical Absorption Properties of Lead-Free Metal Halide Perovskites and Double Perovskites

Weiwei Meng; Xiaoming Wang; Zewen Xiao; Jianbo Wang; David B Mitzi; Yanfa Yan

doi:10.1021/acs.jpclett.7b01042

Parity-Forbidden Transitions and Their Impact on the Optical Absorption Properties of Lead-Free Metal Halide Perovskites and Double Perovskites

J Phys Chem Lett. 2017 Jul 6;8(13):2999-3007. doi: 10.1021/acs.jpclett.7b01042. Epub 2017 Jun 16.

Authors

Weiwei Meng^{1

2}, Xiaoming Wang¹, Zewen Xiao¹, Jianbo Wang^{2

3}, David B Mitzi⁴, Yanfa Yan¹

Affiliations

¹ Department of Physics and Astronomy and Wright Center for Photovoltaic Innovation and Commercialization, The University of Toledo , Toledo, Ohio 43606, United States.
² School of Physics and Technology, Center for Electron Microscopy, MOE Key Laboratory of Artificial Micro- and Nano-structures, and Institute for Advanced Studies, Wuhan University , Wuhan 430072, China.
³ Science and Technology of High Strength Structural Materials Laboratory, Central South University , Changsha 410083, China.
⁴ Department of Mechanical Engineering and Materials Science and Department of Chemistry, Duke University , Durham, North Carolina 27708, United States.

PMID: 28604009
DOI: 10.1021/acs.jpclett.7b01042

Abstract

Using density functional theory calculations, we analyze the optical absorption properties of lead (Pb)-free metal halide perovskites (AB²⁺X₃) and double perovskites (A₂B⁺B³⁺X₆) (A = Cs or monovalent organic ion, B²⁺ = non-Pb divalent metal, B⁺ = monovalent metal, B³⁺ = trivalent metal, X = halogen). We show that if B²⁺ is not Sn or Ge, Pb-free metal halide perovskites exhibit poor optical absorptions because of their indirect band gap nature. Among the nine possible types of Pb-free metal halide double perovskites, six have direct band gaps. Of these six types, four show inversion symmetry-induced parity-forbidden or weak transitions between band edges, making them not ideal for thin-film solar cell applications. Only one type of Pb-free double perovskite shows optical absorption and electronic properties suitable for solar cell applications, namely, those with B⁺ = In, Tl and B³⁺ = Sb, Bi. Our results provide important insights for designing new metal halide perovskites and double perovskites for optoelectronic applications.