Disclosed is a method for making a nickel film for use as an electrode of an n-p diode or solar cell. A light source is used to irradiate an n-type surface of the n-p diode or solar cell, thus producing electron-hole pairs in the n-p diode or solar cell. For the electric field effect at an n-p interface, electrons drift to and therefore accumulate on the n-type surface. With a plating agent, the diode voltage is added to the chemical potential for electroless plating of nickel on the n-type surface. The nickel film can be used as a buffer layer between a contact electrode and the diode or solar cell. The nickel film reduces the contact resistance to prevent a reduced efficiency of the diode or solar cell that would otherwise be caused by diffusion of the atoms of the electrode in following electroplating.