High efficiency amorphous silicon germanium solar cells

We report high-efficiency single-junction a-SiGe n-i-p solar cells deposited using rf PECVD on stainless steel (SS) substrates coated with metal/ZnO back-reflector (BR). The initial and stabilized active-area efficiencies have been improved to 12.5-13.0% and 10.4%, respectively, for 0.25 cm² a-SiGe cells. The achievement of single-junction cells with such high efficiencies, equivalent to those for the state-of-the-art triple-junction solar cells, are important since this would lead to significant cost reduction in manufacturing. The key factors leading to these high efficiencies include the use of: 1) an optimized GeH₄ to Si₂H₆ ratio leading to a Ge content ideal for high-efficiency single-junction a-SiGe cell, 2) an optimized level of hydrogen dilution for the i-layer, and, most importantly, 3) a hybrid p-layer with the sub-layer near a-SiGe i-layer deposited at high temperature (140 °C) and the bulk of the p-layer deposited at low temperature (70 °C) for better transparency.