Semitransparent Cu2O films based on CuO Back Layer for Photoelelctrochemical Water Splitting and Photovoltaic Applications

Cuprous oxide (Cu2O) as an intrinsic p‐type semiconductor is promising for solar energy conversion. The major challenge in fabricating Cu2O lies in achieving both high transparency and high performance in a tandem device. The Cu2O photocathodes often employ gold as the back contact layer. However, it is not an optimal choice in tandem device due to its poor transmission, scarcity, and electron‐hole recombination at the interface of Au and Cu2O. Here, we presented a facile method that utilizes the earth‐abundant material copper oxide (CuO) to fabricate highly transparent Cu2O devices. The maximum transmittance of the Cu2O film on CuO (FTO/CuO/Cu2O) increased from 42% to 58% compared with Cu2O film on Au (FTO/Au/Cu2O) in 550‐800 nm. After coating atomic layer deposition (ALD) layers and hydrogen evolution reaction (HER) catalyst, the photocurrent density at 0 V (versus RHE) of the semitransparent Cu2O photocathode with CuO as the back layer for photoelectrochemical (PEC) water splitting reached ‐4.9 mA·cm‐2, which showed a 24.5% improvement compared with FTO/Au/Cu2O photocathode. Moreover, expanding the CuO layer strategy to the field of solar cells enables Cu2O solar cells to achieve a PCE of 2.37%.