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. Preliminary cell efficiency has reached 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. Agnanoparticle 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 (VOC) and short-circuit current density (JSC) 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 tube furnaces. While this passivation is effective, it is not yet 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 8to 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. Black Si solar cells with LPD SiO2 passivation also demonstrate 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 crystalline Si solar cells. Index Terms — black silicon, metal-assisted porous silicon etching, antireflection, liquid phase deposition, surface passivation, photovoltaic cells.