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 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.

Duke Scholars

Author David Mitzi Thomas Lord Department of Mechanical Engineering and Materia ...