Low-defect Cu2O films with vertical grains via tartaric acid assisted solution growth for efficient photoelectrochemical water splitting

Cu 2 O is among the most promising metal oxide semiconductors for solar water splitting, yet its performance is often limited by structural defects and poor charge transport. Here, we report a tartaric acid-assisted solution growth strategy to fabricate high-quality Cu 2 O films (T-Cu 2 O) with reduced defect density, prolonged carrier lifetimes, and enhanced electrical conductivity. Microstructural analysis reveals that T-Cu 2 O films consist of vertically aligned columnar grains exceeding 1 μm in length, spanning the entire film thickness. This contrasts with the disordered grains formed in conventional lactic acid-assisted films (L-Cu 2 O), which impede charge transport. Upon integration with overlayers and RuO x cocatalysts, the T-Cu 2 O photocathode delivers a photocurrent density of 8.0 mA cm –2 at 0 V vs . RHE—23% higher than its L-Cu 2 O counterpart. Surface photovoltage measurements further confirm significantly improved charge separation in T-Cu 2 O. This work establishes a facile solution-based strategy for producing high-quality Cu 2 O photoelectrodes with enhanced efficiency for photoelectrochemical water splitting.