A method for forming a nickel oxide layer is disclosed herein. In some embodiments, a method includes depositing a nickel oxide precursor ink on a substrate, wherein the nickel oxide precursor ink comprises a solvent comprising diols, alcohol amines, and water, Ni(NO3)2·6H2O, and at least one metal acetate selected from the group consisting of Ni(CH3CO2)2·4H2O and Cu(CH3CO2)2·1H2O, annealing the nickel oxide precursor ink at a temperature between 250° to 400° Celsius for between 10 minutes and 6 hours to form a nickel oxide layer, and cooling the nickel oxide layer.