Formamidinium-Containing Metal-Halide: An Alternative Material for Near-IR Absorption Perovskite Solar Cells

Solid-state, solution processed solar-cells based on organic–inorganic methyl ammonium lead halide absorbers have achieved efficiencies in excess of 15%, which has superseded liquid dye sensitized cells, as well as various thin film-based photovoltaics. This report introduces a new metal-halide perovskite, based on the formamidinium cation (HC(NH 2 ) 2 + ), that displays a favorable band gap (1.47 eV) and represents a broader absorption compared to previously reported absorbers that contained the methylammonium cation (CH 3 NH 3 + ). The high open-circuit voltage ( V oc = 0.97 V) and promising fill-factor (FF = 68.7%) yield an efficiency of 4.3%, which make this material an excellent candidate for this new class of perovskite solar cell. This report also investigates the formation of a black trigonal ( P 3 m 1) perovskite polymorph and a yellow hexagonal nonperovskite ( P 63 mc ) polymorph. Further solar cell development would entail the stabilization of the black trigonal ( P 3 m 1) perovskite polymorph over the yellow hexagonal nonperovskite ( P 63 mc ) polymorph.