Abstract
Electrochemical etching was used to form a nanoporous silicon (PS) layer on the surface of a crystalline silicon wafer. The PS layer works as an anti-reflection coating to reduce the reflection of the incident light into the solar cell. The etching solution was prepared by mixing HF (50 \%) and ethanol, which was introduced for efficient bubble elimination on the silicon surface during the etching process. The anodization of the silicon surface was performed under a constant current, and process parameters, such as current density, etching time, and volume fraction of HF to ethanol in the solution, were carefully tuned to minimize the surface reflectance of the CZ silicon wafer with sheet resistance of 35 $\sim$ 40 $\Omega/\Box$. The PS layer as an anti-reflection layer in the solar cell was compared with a conventional SiN$_x$ coating deposited using plasma-enhanced chemical-vapor deposition. The photovoltaic properties of the cells with PS layers were confirmed by the measurements of the quantum efficiency.