The Influence of Post H2-Plasma Treatment to the Performance of Solar Cells

The interface properties of amorphous silicon (a-Si:H) solar cells have a large influence on the solar cell performance, especially that of the p/i interface. For highly efficient a-Si:H solar cells, a good p/i interface region with low defect density is necessary. In this contribution we report the influence of H2-plasma exposure of the intrinsic layer near the p/i interface on the solar-cell performance. During processing of n-i-p a-Si:H solar cells with PECVD, we exposed the i-layer to a H2-plasma before p-type a-SiC:H deposition. With this treatment, the Voc and FF increased significantly, as well as the external quantum efficiency in the wavelength range from 300 nm to 600 nm. The initial efficiency increases from 6.3% (without H2-plasma treatment) to 8.4% (with H2-plasma treatment for 450 s). We think that this performance enhancement can be explained by a reduction of the defect density in the i-layer near the p/i interface following H2-plasma exposure. Additionally, the exposed subsurface layer has a higher mobility band gap, which can act as graded buffer layer to suppress the band offset between the intrinsic a-Si:H layer and ptype a-SiC:H layer. This band gap increase is confirmed by activation energy measurements.