Variation in Absorber Layer Defect Density in Amorphous and Microcrystalline Silicon Thin Film Solar Cells with 2 MeV Electron Bombardment

The effect of the defect density in hydrogenated amorphous and microcrystalline silicon (a-Si:H and µc-Si:H) absorber layers on the performance of thin film solar cells was investigated. The defect density was varied reproducibly over more than two orders of magnitude by 2 MeV electron bombardment and subsequent thermal annealing. Considerable quantitative and qualitative differences were observed for the dependences of the cells parameters on the defect densities of a-Si:H and µc-Si:H. The experimental data suggest further possible improvement of µc-Si:H based solar cells with further reduced defect densities, while for a-Si:H based solar cells, a saturation of performance is observed below a defect density of about 1016 cm-3. Moreover, the experimental data provide an excellent database for numerical simulation over a range unavailable so far particularly in µc-Si:H based solar cells.