A solar cell comprises a substrate, and a metal electrode layer, a p-i-n junction, and a transparent electrode layer which are successively laminated on the substrate. The process comprises the steps of: combining a boron-containing salt, at least one of a metal and its hydride; wherein the metal is Be, Mg, Ca, Sr, Ba, Al, Ga, Si or a transition metal; and a solvent in which the borohydride compound is soluble; grinding a mixture formed in step to form the borohydride compound; and separating a solution comprising the borohydride compound. In various embodiments, the control is indicative of status of at least one parameter for at least one device.