Title : Synergistic light trapping and plasmonic enhancement in black silicon-based photocathodes for photoelectrochemical water splitting
Abstract:
This study presents a black silicon-based photocathode for photoelectrochemical water splitting toward sustainable solar hydrogen production. Black silicon (b-Si) was employed as an efficient photoabsorber because its highly textured surface enables strong light trapping and broadband suppression of optical reflection. Randomly distributed inverted-pyramid-like microstructures were successfully formed on the p-type Si surface. These sharp micrometer-scale features provided multiple light scattering pathways and resulted in ultralow diffuse reflectance. Notably, the fabricated b-Si maintained very low reflectance even in the long-wavelength region above 1100 nm, demonstrating its capability for broad solar spectrum utilization. To address the interfacial instability and charge recombination issues of Si-based photocathodes, an oxide passivation layer was introduced onto the b-Si surface. This oxide layer improved chemical stability and promoted interfacial charge separation by forming a heterojunction with p-type Si. In addition, it served as an electron transport layer, which facilitated charge extraction from the Si absorber to the catalytic surface. The successful formation of the oxide layer was confirmed by structural and elemental analyses, although further optimization of coating conformality is required for highly textured b-Si surfaces. Au nanoparticles were further incorporated as localized surface plasmon resonance (LSPR)-active catalysts. Optical measurements revealed that Au nanoparticle deposition additionally reduced the diffuse reflectance of b-Si, indicating a plasmon-assisted anti-reflection effect.
The Au nanostructures enhanced the localized electromagnetic field near the photocathode surface and promoted hot carrier generation. These effects improved photon utilization and supported more efficient charge separation during photoelectrochemical operation. The role of each component was verified by comparing bare Si, b-Si, b-Si/oxide and b-Si/oxide/Au photocathodes. The integrated b-Si/oxide/Au photocathode demonstrated enhanced photocurrent response, improved onset behavior and higher operational stability compared with unprotected b-Si. Wavelength-dependent photoelectrochemical measurements further confirmed the correlation between Au-induced optical enhancement and photocurrent generation. These results suggest that the combination of b-Si light management, oxide passivation and plasmonic Au catalysis provides an effective platform for efficient and stable solar hydrogen evolution.
