Diffused junction optimization in silicon solar cells by a photochemical method

Abstract

To obtain the maximum conversion efficiency for a p +-n-n + polycrystalline silicon solar cell fabricated by thermal diffusion at elevated temperatures, it is essential to remove the dead layer formed on the p + side after diffusion. To remove the dead layer or to optimize the junction depth a new method is described which is highly controllable and requires almost no expensive apparatus. In this method a film of silicon oxide is grown photoelectrochemically over the p + region and a part (about 600 Å thick) of the top of the p + region is consumed in growing this silicon oxide film which is 750 Å thick. When this film is stripped off in a dilute aqueous NaOH solution, a reduction in the junction depth is achieved and in this way the junction depth can be optimized to extract the maximum power from the solar cell. Grain boundaries do not seem to affect the growth and stripping rates of the thin film appreciably and a polycrystalline cell shows an appreciable improvement in the short-circuit current with no significant decrease in the shunt resistance.