Stable Hydrogenated Amorphous Silicon Germanium for Photovoltaic Applications. Experimental and Computational Studies

Abstract

The research was aimed at the optimisation of low band gap amorphous silicon germanium (a-SiGe:H) materials with special emphasis on developing a highly absorbing material with high stability against light soaking when incorporated in thin film solar cells. Of particular interest is the growth of protocrystalline a-SiGe:H, which is obtained by depositing the material near the threshold of microcrystalline formation. This kind of material embodies an improved medium range order, which is in this study identified as the reason for enhanced stability. Technologically friendly deposition conditions for stable a-SiGe:H material were investigated. Among them, substrate temperatures (160 ºC) closer to the deposition temperature of the previously deposited layers (electrodes, doped layers) and the use of disilane as the feedstock gas to obtain higher deposition rates are the important parameters. The scope of the research ranges from the experimental application of the a-SiGe:H material in single and tandem solar cells to numerical simulations of these p-i-n structures. The detailed understanding of the single junction a-SiGe:H solar cell behaviour in the dark and under illumination conditions by computer modelling opened new opportunities for improving the performance of a-SiGe:H solar cells. This procedure can be applied to the improvement of stabilized single junction cells.