Antireflection and SiO2 surface passivation by liquid-phase chemistry for efficient black silicon solar cells

We report solar cells with both black Si antireflection and SiO₂ surface passivation provided by inexpensive liquid-phase chemistry, rather than by conventional vacuum-based techniques. The best cell efficiency from our first efforts was 16.4%. Nanoporous black Si antireflection on crystalline Si by aqueous etching promises low surface reflection for high photon utilization, together with lower manufacturing cost compared to vacuum-based antireflection coating. Agn-anoparticle-assisted black Si etching and post-etching chemical treatment recently developed at NREL enables excellent control over the pore diameter and pore separation. Performance of black Si solar cells, including open-circuit voltage, short-circuit current density, and blue response, has benefited from these improvements. Prior to this study, our black Si solar cells were all passivated by thermal SiO₂ produced in a tube furnace. Although this passivation is effective, it is not ideal for ultra-low-cost manufacturing. In this study, we report, for the first time, the integration of black Si with a proprietary liquid-phase deposition (LPD) passivation from Natcore Technology. The Natcore LPD forms a layer of <;10-nm SiO₂ on top of the black Si surface in a relatively mild chemical bath at room temperature. We demonstrate black Si solar cells with LPD SiO₂ with a spectrum-weighted average reflection lower than 5%, similar to the more costly thermally grown SiO₂ approach. However, LPD SiO₂ provides somewhat better surface-passivation quality according to the lifetime analysis by the photo-conductivity decay measurement. Moreover, black Si solar cells with LPD SiO₂ passivation exhibit higher spectral response at short wavelength compared to those passivated by thermally grown SiO₂. With further optimization, the combination of aqueous black Si etching and LPD could provide a pathway for low-cost, high-efficiency - rystalline Si solar cells.