Development of a metal-assisted chemical etching method to improve light-capture in monocrystalline silicon solar cells

We present here a thorough study of a one-step metal-assisted chemical etching (MACE) method to reduce the reflectivity of monocrystalline silicon (mono c-Si) wafers, thus increasing their light capture efficiency. The method uses hydrogen peroxide (H2O2) and hydrofluoric acid (HF) as etchants and silver (Ag) as reaction catalyst. In this study, we inspected the impact of the etchant molar ratio (rho = [HF]/(HF + H2O2]) in the reaction dynamics and the properties of the etched wafers. For each texturing solution used the etching time was swept, thus characterizing the process evolution over time. The results obtained showed that solutions with a lower molar ratio are more reactive, making the etching process particularly fast. Reflectance measurements proved the capability of the MACE process to sharply reduce the reflectance in the range 350-1100 nm. Scan electron microscope (SEM) observations confirmed the random nature of obtained nanostructures. For several etchant solutions tested an effective reflectivity (Reff) lower than 5% was obtained and a minimum of Reff = 3.0% for rho = 0.916 was reached.