Optimization of etching time for enhanced broadband absorption in flexible black silicon on stainless steel foil

This paper presents optimization of etching time in metal-assisted chemical etching (MACE) process for enhanced broadband absorption in flexible black silicon (b-Si) on stainless steel (SS) foil. Flexible monocrystalline silicon (mono c-Si) wafers with 65 μm thickness are used in this work. For the optimization of etching time, one-step MACE process is utilized with 10−25 min etching to fabricate the b-Si absorber. The SS foil beneath the b-Si also acts as a back reflector (BR) which ensures zero transmission loss in the long wavelength region (above 800 nm). After 20 min etching, b-Si with average nanowires (NWs) length of 982 nm is formed. This condition exhibits the lowest average weighted reflection (AWR) and the highest broadband light absorption in the b-Si within 300−1100 nm wavelength region, owing to refractive index grading effect at the air/b-Si interface. This corresponds to the maximum potential short-circuit density (Jsc(max)) of 39.3 mA/cm2, or 62.4 % enhancement when compared to the planar c-Si reference. The findings demonstrate the potential of flexible b-Si on SS foil to deliver high photocurrent in the future solar cells.