Light-Induced Plating of Aluminum on Silicon in an Ionic Liquid

Abstract

As the consumption of silver for the front electrode in silicon solar cells continues to grow rapidly, a low-cost low-resistivity Earth-abundant metal is likely needed to replace silver. Besides the widely-studied copper, aluminum is another candidate for front metallization in silicon solar cells. Conventional electroplating of aluminum in a nonaqueous ionic liquid has been carried out on silicon solar cells and about 18% efficiency has been demonstrated with an electroplated aluminum front electrode. However, the high-resistivity silicon substrate requires a nickel seed layer to facilitate aluminum electroplating on it. In this talk, we report light-induced plating of aluminum directly on the n side of a silicon p-n junction in an ionic liquid. Without any seed layer, the deposited aluminum has good adhesion to the silicon surface. The resistivity of the aluminum deposits is as low as 4×10–6 Ω-cm, which is only about 1.5 times that of bulk aluminum. The suitable wavelength for the light source is between 600 nm to 1,000 nm. The effect of plating temperature on morphology of the aluminum deposits is analyzed. Our light-induced aluminum plating process enables simpler, lower-cost metallization on silicon solar cells than the copper plating process.