Semitransparent CuO Films Based on CuO Back Layer for Photoelectrochemical Water Splitting and Photovoltaic Applications.

Cuprous oxide (CuO) as an intrinsic p-type semiconductor is promising for solar energy conversion. The major challenge in fabricating CuO lies in achieving both high transparency and high performance in a tandem device. The CuO 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 CuO. Here, we presented a facile method that utilizes the earth-abundant material copper oxide (CuO) to fabricate highly transparent CuO devices. The maximum transmittance of the CuO film on CuO (FTO/CuO/CuO) increased from 42 % to 58 % compared with CuO film on Au (FTO/Au (3 nm)/CuO) 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 CuO photocathode with CuO as the back layer for photoelectrochemical (PEC) water splitting reached -4.9 mA cm, which showed a 24.5 % improvement compared with FTO/Au/CuO photocathode. Moreover, expanding the CuO layer strategy to the field of solar cells enables CuO solar cells to achieve a PCE of 2.37 %.