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 MX.sub.2 and AX dissolved in a first
coating solvent, wherein the
molar ratio of MX.sub.2:AX=1:n with 0<n<1; and applying a second precursor solution to the first precursor
coating to convert the first precursor coating to a
perovskite layer AMX.sub.3, 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 AMX.sub.3 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.