N/I buffer layer for substrate microcrystalline thin film silicon solar cell

The influence of the substrate surface morphology on the performance of microcrystalline silicon solar cells in the substrate or n-i-p (nip) configuration is studied in this paper. The experiments are carried out on glass substrates coated with naturally textured films of ZnO deposited by low pressure chemical vapor deposition which serves as backcontact and as template for the light trapping texture. The film surface morphology can be modified with a plasma treatment which smoothens the V-shaped valleys to a more U-shaped form. We investigate, first, the influence of different substrates morphologies on the performance of microcrystalline (mu c-Si:H) thin film silicon solar cells deposited by very high frequency plasma enhanced chemical vapor deposition. The V-shaped morphologies are found to have strong light trapping capabilities but to be detrimental for the mu c-Si:H material growth and lead to degraded open circuit voltage (V-oc) and fill factor (FF) of the solar cells. Hence, in Sec. III B, we introduce a buffer layer with a higher amorphous fraction between the n doped and intrinsic layer. Our study reveals that the buffer layer limits the formation of voids and porous areas in the mu c-Si:H material on substrates with strong light trapping capabilities. Indeed, this layer mitigates V-oc and FF losses which enhances the performance of the mu c-Si:H solar cell. Finally, by applying our findings, we report an efficiency of 9% for a nip mu c-Si:H thin film silicon cell with a thickness of only 1.2 mu m.