Micro-textures with large opening angles and smooth U-shape are applied to nanocrystalline silicon (nc-Si:H) solar cells. The micro-textured substrates result in higher open-circuit-voltage (Voc) and fill-factor (FF) than nano-textured substrates. For thick solar cells, high Voc and FF are maintained. Particularly, the Voc only drops from 564 to 541 mV as solar cell thickness increases from 1 to 5 μm. The improvement in electrical performance of solar cells is ascribed to the growth of dense nc-Si:H layers free from defective filaments on micro-textured substrates. Thereby, micromorph tandem solar cells with an initial efficiency of 13.3%, Voc = 1.464 V, and FF = 0.759 are obtained.
This study gives a guideline on developing high bandgap, high quality hydrogenated amorphous silicon (a-Si:H) through a carefully engineered nanostructure. Single-junction a-Si:H solar cells with open-circuit voltages (Voc) above 950 mV and conversion efficiencies above 9% are realized by processing the absorber layers at high pressures of 7–10 mbar. The high Voc is a result of an increased bandgap, which is attributed to an increase in the average size of the open volume deficiencies in the absorber layer without a significant increase in the nanosized void density.
In this work we demonstrate excellent c-Si surface passivation by depositing a-Si:H in the high-pressure and high hydrogen dilution regime. By using high hydrogen dilution of the precursor gases during deposition the hydrogen content of the layers is sufficiently increased, while the void fraction is reduced, resulting in dense material. Results show a strong dependence of the lifetime on the substrate temperature and a weaker dependence on the hydrogen dilution. After applying a post-deposition annealing step on the samples equilibration of the lifetime occurs independent of the initial nanostructure.
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