Broadband Anti-Reflection in Black Silicon Fabricated by Two-Step Silver-Assisted Wet Chemical Etching for Photovoltaics

This paper reports broadband anti-reflection in black silicon (b-Si) fabricated by two-step metal-assisted chemical etching (MACE) for potential photovoltaic (PV) applications. The method involves deposition of silver nanoparticles (Ag NPs) in aqueous solution of HF:AgNO3, followed by etching in HF:H2O2:DI H2O solution for different duration (10-25 s). Effects of etching time towards surface morphological and optical properties of b-Si nanowires are investigated. Surface morphological characterization confirms presence of b-Si nanowires with heights of 350-570 nm and diameter of 150-300 nm. The b-Si nanowires exhibit outstanding broadband anti-reflection due to refractive index grading effect. This is represented as weighted average reflection (WAR) in the 300-1100 nm wavelength region. After 20 s of etching, b-Si nanowires with height of 570 nm and width of about 200 nm are produced. The nanowires demonstrate WAR of 5.5%, which represents the lowest WAR in this investigation. This results in absorption of 95.6% at wavelength of 600 nm. The enhanced broadband light absorption yields maximum potential short-circuit current density (Jsc(max)) of up to 39.7 mA/cm2, or 51% enhancement compared to c-Si reference. This facile b-Si fabrication method for broadband enhanced anti-reflection could be a promising technique to produce potential PV devices with high photocurrent.