Abstract: Semiconductor devices including a cathode layer, an anode layer, an active layer disposed between the cathode layer and the anode layer, wherein the active layer includes a perovskite layer, and a passivation layer disposed directly on a surface of the active layer between the cathode layer and the active layer, the passivation layer including a zwitterionic amino acid, such as valine or phenylalanine or other amino acid that passivates both cationic and anionic defects in the surface of the active layer.

Abstract: Perovskite materials useful in the manufacture of photovoltaic cells are provided. The perovskite materials have the formula AB?0.5B?0.5X3 or A?0.5A?0.5B?0.5B?0.5X3, wherein A, A?, and A? are organic or inorganic cations, X is a halogen ion, B? is tin, and B? is germanium. Embodiments of the mixed tin and germanium halide perovskite materials possess a direct bandgap within the optimal range of 0.9-1.6 eV and have an optical absorption spectrum that is comparable to the state-of-the-art methylammonium lead iodide perovskites. The perovskite materials provided herein have been formulated to be lead-free.