A-Si:H solar cells using the hot-wire technique-how to exceed efficiencies of 10%

In this study we describe our latest efforts to improve the efficiency and stability of hot-wire (HW-) a-Si:H based solar cells by further optimizing p/i-interface and i-layer quality. In-situ ellipsometry has been used to determine the film microstructure (density, roughness) at the crucial p/i-interface and of the fully grown i-layers. A detailed investigation of the effect of varying the process gas pressure, p and filament temperature, T_fil enabled us to improve the interface and bulk i-layer quality significantly. The microstructure, especially at the p/i-interface but also of the i-layer, has been found to sensitively correlate with the cell performance. The resulting solar cells exhibited efficiencies as high as 9.7% although there are two “air breaks”, sputtered n-layers and simple evaporated aluminum rear contacts. Moreover, for the first time we report on results concerning the effect of hydrogen dilution on the stability of HW-a-Si:H i-layers and solar cells