A-Si:H/c-Si heterojunctions: a future mainstream technology for high-efficiency crystalline silicon solar cells?

In this contribution, we shortly review the main features of amorphous /crystalline silicon heterojunction (SHJ) solar cells, including interface defects and requirements for high quality interfaces. We show how a process flow with a limited number of process steps leads to screen printed solar cells of 2×2cm² with 21.8% efficiency and of 10×10cm² with 20.9% efficiency (n-type FZ). We show that the devices work in high injection conditions of 3×10¹⁵cm^-3 at the maximum power point, a factor two higher than the base doping. Several research labs and companies can now produce large area 6" cells well over 20% on CZ wafers and some of the critical cost factors, such a metallization can be overcome with suitable strategies. Based on the high quality coating tools and processes developed for thin films used for flat panel display or thin film solar cell coatings, the deposition of the layers required to make SHJ cells has the potential to be performed in a controlled way at low cost. Considering the few process steps required, the high quality n-type Cz wafers that can be obtained by proper crystal growth control, SHJ technology has several assets that could make it become a widespread PV technology.