Influence of surface treatments on crystalline germanium heterojunction solar cell characteristics

Hydrogenated amorphous Si (a-Si:H) has been applied to crystalline germanium (c-Ge) heterojunction solar cells and the influence of the surface treatments applied before a-Si:H deposition process has been studied. We found that PH3 exposure treatment after surface oxide removal by annealing is effective to improve c-Ge heterojunction solar cell performance. The conversion efficiency of the c-Ge heterojunction solar cell applied PH3 exposure treatment was up to 5.29% and the solar cell had better temperature coefficient than the c-Ge homojunction solar cell. These results suggest that the c-Ge substrate surface after oxide removal by annealing is covered with negatively charged dangling bonds, and the phosphorus adsorbed onto the c-Ge surface provides electron as a donor and corrects the band bending induced by negatively charged dangling bonds.