Wet-chemical treatment and electronic interface properties of silicon solar cell substrates

On textured n-type silicon substrates for solar cell manufacturing, the relation between light trapping behavior, structural imperfections, energetic distribution of interface state densities and interface recombination losses were investigated by applying surface sensitive techniques. The field-modulated surface photovoltage (SPV), in-situ photoluminescence (PL) measurements, total hemispherical UV-NIR-reflectance measurements and electron microscopy (SEM) were employed to yield detailed information on the influence of wet-chemical treatments on preparation induced micro-roughness and electronic properties of polished and textured silicon substrates. It was shown that isotropic as well as anisotropic etching of light trapping structures result in high surface micro-roughness and density of interface states. Removing damaged surface layers in the nm range by wet-chemical treatments, the density of these states and the related interface recombination loss can be reduced. In-situ PL measurements were applied to optimise HF-treatment times aimed at undamaged, oxide-free and hydrogen-terminated substrate surfaces as starting material for subsequent solar cell preparations.