Improving the Performance of Thin Film Radial Junction Solar Cells

29th European Photovoltaic Solar Energy Conference and Exhibition; 46-49
Due to a unique structure, a silicon nanowire matrix provides natural light trapping and anti-reflection effects suitable for photovoltaic applications. Thus depositing thin film silicon directly on top of them and forming radial junctions is a promising approach for a new generation of efficient solar cells. Apart from the light trapping, their major advantage is decoupling of the light absorption from the carrier collection direction. This allows the use of very thin active layer, providing more efficient collection in materials with low minority carrier diffusion lengths and also minimizes the light-induced degradation. It has been found that the density of radial junctions is a very important parameter for controlling the device performances. By optimizing the nanowire density, we have demonstrated 8.1 % efficiency for PIN hydrogenated amorphous silicon (a-Si:H) solar cells deposited directly on the TCO coated glass with only 100 nm of active layer thickness. We have adopted two different approaches to improve the short-circuit current density and open-circuit voltage. Firstly, replacing n-type a-Si:H by more transparent amorphous silicon oxide has enhanced the blue response of the solar cell. Secondly, we have shown that a p-type a-Si:H coating on the crystalline silicon nanowire, before depositing the intrinsic layer, is very effective in reducing the nanowire surface recombination and consequently increasing the open-circuit voltage.