Autogenic single p/n-junction solar cells from black-Si nano-grass structures of p–to–n type self-converted electronic configuration
Photovoltaic performance of solar cells automatically improves when the absorber-layer itself simultaneously plays as the anti-reflection nanostructure with enhanced active-absorber-area on the front surface. Combined physical and chemical etching of p–c-Si wafers by (Ar+H2)-plasma in inductively coupled low-pressure plasma-CVD produce various nanostructures with subsequent minimization of reflectance. At reduced temperature, the rate-constant of thermal diffusion of atomic-H in the Si-network weakens, leading to its enhanced chemical etching reactions that further increase at elevated RF power. Regrowth of the SiHn precursors produced by etching and subsequent hydrogenation in the plasma develops high-density of elongated nano-grass structures, which further align with sharp tips via Ar+ ion bombardment and elimination of loosely-bound amorphous over-layers, on application of negative dc substrate bias during real-time etching-and-regrowth. Significantly reduced reflectance (~0.5%) via coherent light trapping within the uniformly distributed vertically aligned nano-grass surfaces evolves truly black-silicon (b-Si) nanostructures, which further self-convert from the p-type to n-type electronic configuration via etching mediated modification of B-H bonds from BH1 to BH2 and/or BH3 states, producing autogenic p/n-junctions. Using (Ar+H2)-plasma etched b-Si nano-grass structures, low-temperature (~200°C) and one-step-fabrication of autogenic single p/n-junction proof-of-concept solar cells are accomplished. There’s plenty of room for further progress in device performance.