Enabling Unassisted Solar Water Splitting by Single-Junction Amorphous Silicon Photoelectrodes

Amorphous silicon (a-Si) has been extensively used to fabricate solar cells for efficient light-to-electricity conversion due to its outstanding light-harvesting properties and its facile and low-cost preparation method. However, photoelectrodes based on single-junction-structured a-Si have not been demonstrated for overall water splitting due to their insufficient photovoltage. Herein, we report the fabrication of single-junction a-Si-based photocathodes and photoanodes and further construct dual-photoelectrode devices for unassisted photoelectrochemical (PEC) water splitting. The p/i/n and n/i/p junction a-Si are used as photoabsorbers and the sputtered Pt nanoparticles and Co₃O₄ film as cocatalysts for photocathodes and photoanodes, respectively. The photocathode yields a photocurrent density up to 12.03 mA cm^-2 at 0 V versus reversible hydrogen electrode (RHE), which outperforms all previous results of a-Si-based photocathodes for PEC hydrogen evolution reactions. Additionally, the Co₃O₄/nip photoanode generated a photocurrent density of 7.3 mA cm^-2 at 1.23 V vs RHE. The maximum applied bias photo-to-current efficiencies are 3.3% for the photocathode and 0.93% for the photoanode in alkaline solution. The as-fabricated biphotoelectrode system is able to yield a solar-to-hydrogen efficiency of 0.61%, which presents an example enabling single-junction-structured a-Si for unassisted overall water splitting.