Highly efficient p–n Cu2O homojunction photocathodes for unassisted solar water splitting

As a promising photocathode material, p-n Cu₂O still suffers from intrinsic photocorrosion and a limited electron diffusion length in aqueous electrolytes. Herein, p–n Cu₂O homojunction films were synthesized via a simple sequential potentiostatic deposition process. The inherent electric field within the homojunction yields Cu₂O photocathode with significantly enhanced charge carrier separation and improved stability. Compared with single p-Cu₂O, the stability of the optimized p-n Cu₂O composite photocathode increased from 11 % to 40 % over 300 s. Furthermore, the p-n Cu₂O/Pt photocathode exhibited an excellent photocurrent density (J_ph) of −5.1 mA cm⁻² at 0 V versus RHE, which is 1.58 times higher than that of p-n Cu₂O. When integrated with the BiVO₄/Au/NiFeOOH photoanode developed in our previous work to obtain an unbiased water-splitting apparatus, the J_ph remained stable at approximately 0.25 mA cm⁻² for nearly 5 h.