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

• Published in: The journal of physical chemistry letters 2017-07, Vol.8 (13), p.2999-3007
• Main Authors: Meng, Weiwei, Wang, Xiaoming, Xiao, Zewen, Wang, Jianbo, Mitzi, David B, Yan, Yanfa
• Format: Article
• Language: English
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.7b01042

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.