Analysis and optimization of the bulk and rear recombination of screen-printed PERC solar cells

Abstract

In this paper, we investigate the impact of the rear surface passivation, the silicon base material and the local aluminum contacts applied to rear side passivated solar cells with a homogenously doped emitter at the front. We compare different dielectric surface passivation layers (SiO2, Al2O3, SiNx) on a high-efficiency level using 125×125 mm2 and 156×156 mm2 p-type Cz silicon wafers. It turns out that applying an Al2O3/SiN x layer stack outperforms all other surface passivation layers due to its excellent surface passivation as well as optical properties. We determine the impact of the light induced degradation depending on the used Cz base material. We measure an efficiency drop between 0.0 % (Ga-doped) and 0.8 % abs. (B-doped) after 8 hours of illumination under 0.5 Suns. We measure the surface recombination velocity of local screen-printed Al contacts with varying the metallisation fraction frear with the dynamic infrared lifetime mapping technique (dyn-ILM) on lifetime samples. We measure a decrease in contact recombination velocity from above 1100 cm/s for small frear to 400 cm/s for large frear on 1.5 Ωcm p-type FZ-silicon. Microscopy investigations show that this is due to an improved local Al-BSF formation when using higher frear.