Effect of Light on Electroless Nickel Deposition for Solar Cell Applications

Abstract

In c-Si solar cell front contact metallization, nickel-copper electroplating scheme is found to be economical compared to other available techniques. In this metallization process, nickel seed layer deposition is looking simple but very important step in terms of its grain size, minimum thickness reaching the continuity of the film and its uniformity. Thin, uniform and continuous nickel seed layer helps in reducing the metal-semiconductor contact resistance as well as prevent junction shunting during silicide formation at the metal-semiconductor interface. Although, there are different process parameters affecting the morphology of the nickel film in electroless chemical bath deposition, but due to the photovoltaic effect of the p-n junction of the solar cell, the ambient light affects the nickel deposition process. The effect of light on electroless nickel (EN) deposition has been studied in this work. For this purpose the experiments have been performed in different lighting conditions like: dark, ambient, varying intensity UV-VIS light. Also, the nickel depositions have been done for different periods of time from very small period like 30s to longer periods like: 1min, 2min, 3min and 4min to see the effect at the initial stage of depositions as well as for prolonged deposition. Alkaline bath (pH ∼7.5) was selected for EN-deposition and other experimental conditions were kept same for all the experiments. EN- deposition under dark is found to be the most suitable for nickel-copper metallization process and it is having some built-in benefits which have been mentioned in this work.