Bandgap Engineering of Stable Lead-Free Oxide Double Perovskites for Photovoltaics

Despite the rapid progress in solar power conversion efficiency of archetype organic-inorganic hybrid perovskite CH₃ NH₃ PbI₃ -based solar cells, the long-term stability and toxicity of Pb remain the main challenges for the industrial deployment, leading to more uncertainties for global commercialization. The poor stabilities of CH₃ NH₃ PbI₃ -based solar cells may not only be attributed to the organic molecules but also the halides themself, most of which exhibit intrinsic instability under moisture and light. As an alternative, the possibility of oxide perovskites for photovoltaic applications is explored here. The class of lead-free stable oxide double perovskites A₂ M(III)M(V)O₆ (A = Ca, Sr, Ba; M(III) = Sb³⁺ or Bi³⁺ ; M(V) = V⁵⁺ , Nb⁵⁺ , or Ta⁵⁺ ) is comprehensively explored with regard to their stability and their electronic and optical properties. Apart from the strong stability, this class of double perovskites exhibits direct bandgaps ranging from 0.3 to 3.8 eV. With proper B site alloying, the bandgap can be tuned within the range of 1.0-1.6 eV with optical absorptions as strong as CH₃ NH₃ PbI₃ , making them suitable for efficient single-junction thin-film solar cell application.