Advanced nanostructuring and gradient phosphorus doping enhance p-Si photocathode performance for photoelectrochemical water splitting

Abstract

This study focuses on enhancing the photoelectrochemical (PEC) performance of p-type silicon (p-Si) solar cells designed for water splitting applications. Black p-Si, utilizing sequential processes including surface damage removal (SDR), cleaning, and metal-assisted chemical etching (MACE) for nanoporous structuring, significantly reduces surface reflectance to ∼1.1%. The subsequent phosphorus doping process in Black n⁺p-Si, achieving a dopant concentration of up to 3 × 10¹⁹ atoms cm⁻³ at the Si surface with a gradient extending up to 700 nm depth, is confirmed. As a result of phosphorus doping, the photocurrent increases to 5.39 mA cm⁻² at 1.23 V compared to the reversible hydrogen electrode (RHE). In potentiometric evaluation, gradient doping yields a photocurrent of 11 mA cm⁻², approximately twice that of Black p-Si at 5 mA cm⁻². The effect of phosphorus doping also improves photocathode functionality, leading to a 15% reduction in charge transfer resistance (R_ct). These results highlight the superior performance of n⁺p-Si, attributed to its unique n–p junction, reducing electron–hole recombination. This study demonstrates significant improvement in PEC performance through gradient doping of nanoporous Black n⁺p-Si and significant PEC stability, thereby expanding its applicability to water splitting.