Transition metal inverse-hybrid perovskites

Abstract

Inverse-hybrid perovskites are related to the photovoltaically promising hybrid perovskites by inverting ion positions. While research of this young materials class focused on main-group elements, here we present an investigation of transition metals (TMs) as mono- or divalent anions in methyl ammonium (MA)₃BA compounds. We find that TMs are best employed on the A-site. First, this allows for favorable tolerance factors in (MA)₃FA compounds and second, most B-site TMs form covalent bonds with neighboring hydrogen atoms or A-site ions, leading to non-perovskite structures. Among the fluoride compounds, group X TMs Ni and Pd yield band gaps of 1.11 eV to 1.35 eV, respectively, low effective masses, and are predicted to have favorable defect tolerance. Thus, they are perfect candidates for photovoltaic applications and are potential lead-free alternatives to MAPbI₃.