This invention relates to an optoelectronic or photovoltaic device comprising a perovskite or metal halide perovskite film treated by one or more compounds of formula (I): ((R1-NH(R2)-R3)+)nW (I), wherein n is an integer selected from 1, 2, or 3; R1, R2, R3 are independently selected from a hydrocarbyl group containing 1-40 carbon atoms said hydrocarbyl group, if said hydrocarbyl group comprises 3 or more carbons, may be linear or branched; and W is an anion.