Heterojunction solar cells based on nanostructured black silicon

The influence of the black silicon (b-Si) morphology on the photovoltaic properties of heterojunction solar cell is investigated. We used cryogenic etching (-150 °C) in a SF₆/O₂ gas mixture to obtain b-Si structures and a total reflectance in the range of 1–3%. The height of the obtained b-Si structures varies from 200 to 760 nm, the shape from nanowires to cone-shaped. The heterojunction a-Si:H/c-Si was fabricated by PECVD at a temperature of 250 °C. The best heterojunction solar cell based on a 200 nm height cone-shaped b-Si demonstrates a promising passivation properties reaching open circuit voltage of 648 mV. With a short-circuit current density of 29.7 mA/cm² and fill factor of 67% a power conversion efficiency of 12.8% was achieved. The solar cells based on cone-shaped b-Si gain also in external quantum efficiency compared to nanowire b-Si.