Methods of making semiconductor perovskite layers and compositions thereof

A method, comprising:

• (a) providing a substrate comprising a hole transport layer;
• (b) applying a solution to said substrate to form a coating of the solution on a surface of the hole transport layer, the solution comprising a perovskite precursor and a solvent, the perovskite precursor comprising a metal halide and organohalides selected from the group consisting of formamidinium chloride, formamidinium bromide, formamidinium iodide, methylammonium chloride, methylammonium bromide, methylammonium iodide, and butylammonium halides, and the solvent comprising N,N′-dimethylpropyleneurea;
• (c) removing the solvent from the coating to form a perovskite precursor layer on the substrate;
• (d) annealing said perovskite precursor layer at a temperature in a range from 40° C. to 120° C. to form a perovskite layer;
• wherein said perovskite layer has a composition of MAn1FAn2Csn3PbX3, where MA is methylammonium, FA is formamidinium, Cs is Cesium, Pb is lead, and X is selected from the group consisting of fluorine, chlorine, bromine, and iodine, wherein n1, n2, and n3 are independently greater than 0 and less than 1 and n1+n2+n3=1;
• (e) applying an electron transport layer to the perovskite layer;
• (f) forming a transparent conducting layer on the electron transport layer, forming the transparent conducting layer comprising creating a buffer layer of a transparent conducting oxide on the electron transport layer using a physical vapor deposition process at a first power and then creating a bulk layer of the transparent conducting oxide on the buffer layer using the physical vapor deposition process at a second power greater than the first power;
• (g) subjecting said perovskite layer, electron transport layer, and transparent conducting layer to an encapsulation lamination process at a temperature of at least 70° C. and at most 130° C. to provide a stack comprising the substrate, the perovskite layer, the electron transport layer, and the transparent conducting layer;
• (h) forming a solar cell using the stack, wherein the perovskite layer in the solar cell retains at least 80% solar conversion efficiency relative to an initial solar conversion efficiency after 300 hours of illumination under one sun conditions at >25° C. and <100° C.