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

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…

• OD
  Ohio Department of Development
• NN
  National Natural Science Foundation of China

  Awards: 51271134, 51501132, 51671148, J1210061, 11674251, 51601132
• MO
  Ministry of Education of the People's Republic of China
• NS
  Natural Science Foundation of Hubei Province

  Awards: 2016CFB446, 2016CFB155
• OO
  Office of Energy Efficiency and Renewable Energy

  Award: DE-EE0006712
• DO
  Division of Materials Research

  Award: DMR-1534686
• DO
  Division of Chemistry

  Award: CHE-1230246