Highly stable hydrogenated amorphous silicon germanium solar cells

This article shows an optimized a-SiGe:H material that behaves highly stable in solar cells. The a-SiGe:H material is deposited by PECVD with high hydrogen dilution, near the microcrystalline deposition regime. We made various a-SiGe:H single solar cells to optimize the device design. The band gap in the central part of the cell is 1.53 eV. The hydrogen bonding configuration in the a-SiGe:H material suggests the presence of voids, however, the material has no noticeable sign of crystallinity. Light soaking experiments showed that the present single junction a-SiGe:H solar cells are highly stable. After one hour of light soaking, a slight improvement in fill factor is observed and an improvement in carrier collection in the red region is evident from spectral response. The stable a-SiGe:H material is incorporated as the bottom cell of a-Si:H/a-SiGe:H tandem solar cells. Unlike the single junction cell, this tandem cell slightly degrades under light soaking. This is solely the result of degradation of the a-Si:H top layer.