The application of poly-Si/SiOx contacts as passivated top/rear contacts in Si solar cells

- Development of both boron and phosphorus doped poly-Si/SiOx contacts featuring film thicknesses below 40 nm.
- Determination of optical properties of poly-Si and quantification of optical absorption losses in poly-Si.
- Solar cell featuring top/rear poly-Si contacts yields Voc=710 mV and FF>81%.

Passivated contacts based on low-pressure chemical vapor deposited (LPCVD) heavily-doped poly-Si and a thin SiOx layer are explored for the application in an interdigitated back contact (IBC) solar cell. The poly-Si/SiOx contacts are realized by applying wet-chemically grown SiOx tunnel layers and amorphous Si (a-Si) layers doped via ion implantation that are subsequently transformed into poly-Si/SiOx contacts by a high temperature step. The impact of doping species, ion dose, and poly-Si thickness on the surface passivation of such contacts is studied. Excellent J0 values down to 4.5 fA/cm2 were measured for n+-poly-Si contacts, while J0 values as low as 22 fA/cm2 were obtained for p+-poly-Si contacts. Solar cells with top/rear poly-Si contacts were processed and Voc values up to 709 mV and FF values above 81% were measured. Furthermore, the upper bound for the parasitic absorption losses in 10-40 nm thick poly-Si films was quantified to be about 0.5 mA/cm2 per 10 nm poly-Si layer thickness.