High efficiency n-type silicon solar cells with passivating contacts based on PECVD silicon films doped by phosphorus diffusion

Abstract

Carrier-selective contacts based on silicon films deposited onto a thin SiOx layer combine high performance with a degree of compatibility with industrial solar cell metallization steps. This paper demonstrates an approach to form electron-selective passivating contacts that maximises the overlap with common industrial equipment; it is based on depositing an intrinsic amorphous silicon (a-Si) layer by PECVD and then doping and re-crystallizing it by means of a thermal phosphorus diffusion. By optimizing the intrinsic a-Si thickness and the phosphorus diffusion temperature, a low recombination current density Joc ≈ 3 fA/cm2 and a low contact resistivity of ρc ≈ 3 mΩ-cm2 have been achieved. Additionally, these electrical parameters have been found to be sensitive to the work function of the outer metal electrode. The application of these optimized electron-selective passivating contacts to n-type silicon solar cells has permitted to achieve a conversion efficiency of 24.7%. A loss analysis has been conducted through Quokka 2 simulations, which together with quantum efficiency measurements, indicate that further optimization should focus on the front boron-doped region of the device.