A process of forming a photoactive layer of a planar perovskite photoactive device comprising: applying at least one layer of a first precursor solution to a substrate to form a first precursor coating on at least one surface of the substrate, the first precursor solution comprising MX2 and AX dissolved in a first coating solvent, wherein the molar ratio of MX2:AX = 1:n with 0 1; and applying a second precursor solution to the first precursor coating to convert the first precursor coating to a perovskite layer AMX3, the second precursor solution comprising AX dissolved in a second coating solvent, the first precursor solution reacting with the second precursor solution to form a perovskite layer AMX3 on the substrate, wherein A comprises an ammonium group or other nitrogen containing organic cation, M is selected from Pb, Sn, Ge, Ca, Sr, Cd, Cu, Ni, Mn, Co, Zn, Fe, Mg, Ba, Si, Ti, Bi, or In, X is selected from at least one of F, Cl, Br or I.