Pure Cubic‐Phase Hybrid Iodobismuthates AgBi 2 I 7 for Thin‐Film Photovoltaics

Bismuth‐based hybrid perovskites are candidates for lead‐free and air‐stable photovoltaics, but poor surface morphologies and a high band‐gap energy have previously limited these hybrid perovskites. A new materials processing strategy to produce enhanced bismuth‐based thin‐film photovoltaic absorbers by incorporation of monovalent silver cations into iodobismuthates is presented. Solution‐processed AgBi 2 I 7 thin films are prepared by spin‐coating silver and bismuth precursors dissolved in n‐butylamine and annealing under an N 2 atmosphere. X‐ray diffraction analysis reveals the pure cubic structure ( Fd 3 m ) with lattice parameters of a = b = c =12.223 Å. The resultant AgBi 2 I 7 thin films exhibit dense and pinhole‐free surface morphologies with grains ranging in size from 200–800 nm and a low band gap of 1.87 eV suitable for photovoltaic applications. Initial studies produce solar power conversion efficiencies of 1.22 % and excellent stability over at least 10 days under ambient conditions.