Light-Induced Effects on the a-Si

Abstract

Light-induced effects on the minority carrier lifetime of silicon heterojunction structures are studied through multiple-exposure photoconductance decay (MEPCD). MEPCD monitors the effect of the measurement flash from a photoconductance decay setup on a sample over thousands of measurements. Varying the microstructure of the intrinsic hydrogenated amorphous silicon (a-Si:H) used for passivation of n-Type crystalline silicon (c-Si) showed that passivating films rich in voids produce light-induced improvement, while denser films result in samples that are susceptible to light-induced degradation. Light-induced degradation is linked to an increase in dangling bond density at the a-Si:H/c-Si interface, while light-induced improvements are linked to charging at the a-Si:H/c-Si interface. Furthermore, doped a-Si:H is added to make samples with an emitter and back surface field (BSF). These doped layers have a significant effect on the light-induced kinetics on minority carrier lifetime. Emitter samples exhibit consistent light-induced improvement, while BSF samples exhibit light-induced degradation. This is explained through negative charging at the BSF and positive charging at the emitter. Full precursors with a BSF and emitter exhibit different kinetics based on which side is being illuminated. This suggests that the light-induced charging at the a-Si:H/c-Si interface can only occur when a-Si:H has sufficient generation.