Fig. 16.

a Atomic structures of CH₃NH₃PbI₃ and CH₃NH₃BiSeI₂, and schematic representation of the split-anion approach for the replacement of Pb in CH₃NH₃PbI₃; b Calculated band gaps of CH₃NH₃BiXY₂ (X = S, Se, Te; Y = Cl, Br, I) using HSE functional with spin–orbit coupling. The dashed line indicates the optimal band gap for single-junction solar cells according to the Shockley–Queisser theory. Adapted with permission from [197]. Copyright (2016) Royal Society of Chemistry