A method for preparing a nickel oxide precursor ink comprising: preparing a solvent comprising diols and alcohol amines; adding nickel nitrate into the solvent to form a nickel nitrate containing solution; adding at least one metal acetate into the nickel nitrate containing solution to form a nickel nitrate and metal acetate containing solution; adding water to the nickel nitrate and metal acetate containing solution to form a nickel oxide precursor mixture; heating the nickel oxide precursor mixture to 60 to 75 Celsius; and cooling the nickel oxide precursor mixture to form the nickel oxide precursor ink.