High-performance silicon-based n–i–p heterojunction photoanode for efficient photoelectrochemical water splitting: fabrication, optimization, and large-scale application†

Considering the ever-growing energy requirements of the evolving world, generation of green hydrogen using the photoelectrochemical (PEC) method holds immense potential. Heterojunction photoelectrodes deliver superior PEC performance by enhancing light absorption, boosting photogeneration of charges, and enabling effective charge separation and transfer with reduced recombination. Herein, a silicon-based state-of-the-art n–i–p heterojunction photoanode with a typical FTO/TiO₂/Si/NiO architecture was fabricated by exploiting all earth-abundant materials, capitalizing on the benefit of the heterostructure. Targeting the practical application of the photoelectrodes for solar fuel production, the widely used and industrially accepted magnetron sputtering technique was employed to fabricate the heterojunction photoanode. The optimized FTO/TiO₂/Si/NiO_A heterojunction photoanode achieved an excellent surface photovoltage of 600 mV and delivered a photocurrent density of ∼0.65 mA cm⁻² at 1.23 V_RHE under simulated solar light illumination (100 mW cm⁻²) with a low onset potential of ∼0.11 V_RHE because of the thoughtful selection of materials in designing the n–i–p device architecture. The n–i–p heterojunction photoanode exhibited excellent photochemical stability over 10 h in a 1 M KOH solution (pH 13.5) with only ∼4% reduction in photocurrent density, signifying its superior and stable PEC performance. The fabricated large-area (25 cm²) n–i–p heterojunction photoanode tested under similar light illumination delivered a high surface photovoltage of 548 mV. The fabrication and demonstration of a large-area photoanode proved the ability of the device architecture for solar-driven water splitting and demonstrated the scalability of the fabrication process for industrial applications.