Improvement of conversion efficiency of multi-crystalline silicon solar cells using reactive ion etching with surface pre-etching

• A large-area antireflection structures were fabricated on mc-Si substrates.
• Surface pre-etching can improve efficiency in combination with RIE process.
• Carrier effective lifetime is an important factor to affect solar cell efficiency.
• An efficiency gain of 0.64% is achieved which compared to wet-textured process.

In this study, a large-area (156 × 156 mm2) sub-wavelength antireflection structure has been fabricated on multi-crystalline Si substrates to reduce their surface reflectivity. A reactive ion etching (RIE) system was used to fabricate nanostructures on the multi-crystalline silicon surface. Reactive gases, comprised of chlorine (Cl2), sulfur hexafluoride (SF6) and oxygen (O2), were activated to fabricate nanoscale pyramids by radio frequency plasma. The pre-etching of poly-Si substrates using acidic and alkaline solutions was studied for creating the microstructures, which may affect the subsequent formation of nano-structures by RIE. Both the solar reflectance and the effective carrier lifetimes of multi-crystalline Si surface are measured to understand the effects of two pre-etching solutions. The pre-etching of silicon wafers using the acidic solution before RIE was found to improve the solar cell efficiency better than that using the alkaline solution. The absolute efficiency of solar cells with acidic pre-etching and RIE texturing can be improved by 0.64% over the traditional conventional cells.