Photo-carrier generation at a-Si layer in SiNx/a-Si stacked passivation with extremely low surface recombination velocity

Abstract

This is to study on the feasibility of photo-carrier generation at amorphous-silicon (a-Si) insertion layer in silicon-nitride (SiN _x )/a-Si stacked passivation system, which realizes extremely low surface recombination velocity (SRV). When the thickness of crystalline silicon (c-Si) becomes thinner than 100 μm for reducing cell cost, the method collecting 100% sun light is to be very important. If a-Si or a-Si-compounds on c-Si in hetero-structure can absorb sun light enough and if the photo-carriers generated inside such a-Si or a-Si compounds are effectively transferred to c-Si and used as currents of c-Si solar cells, the formation of hetero-structure has an advantage for thinning c-Si substrates. In the present research, the ratio of photo-generated carriers in a-Si to the carriers transferred to c-Si is experimentally studied in SiN _x /a-Si stacked passivation system, which is expected to be used as surface passivation of back-contact c-Si solar cells. We compared the SiN _x /a-Si/c-Si system prepared by the plasma-enhanced chemical vapor deposition (PECVD) with that by catalytic chemical vapor deposition (Cat-CVD), often called "Hot-Wire CVD". It is found that the a-Si/c-Si interface prepared by Cat-CVD is much smoother than that by PECVD, indicating better quality of Cat-CVD a-Si/c-Si interface and that almost 100% photo-carriers generated in Cat-CVD a-Si can be transferred into c-Si through the interface when the a-Si thickness is less than 15 nm. This demonstrates the feasibility as power generator for Cat-CVD a-Si in a-Si/c-Si hetero-structure.