Development of a\nRobust p‑Si/p-Cu<sub>2</sub>O/PhC<sub>2</sub>Cu Tandem Photocathode\nfor Photoelectrochemical\nWater Splitting

The photoelectrochemical (PEC) water splitting performance\nof Si-based\nPEC devices is usually restricted by low stability and weak photogenerated\ncarrier transport ability. Herein, a micropyramid array structure\n(p-SiMPs)/p-Cu<sub>2</sub>O/PhC<sub>2</sub>Cu/Pt photocathode device\nwith a p-p-n heterojunction structure is developed. In this tandem\nPEC device, a p-p heterojunction of p-SiMPs/p-Cu<sub>2</sub>O is achieved,\nendowing a higher interface electric field and stronger energy of\nphotoinduced electrons for PEC water reduction. In addition, a stable\nn-type PhC<sub>2</sub>Cu protective layer is prepared on the surface\nof the PEC device by the photoassisted polymerization method, which\ncan improve the stability of PEC water reduction largely. After Pt\ncocatalytic layer deposition, the p-SiMPs/p-Cu<sub>2</sub>O/PhC<sub>2</sub>Cu/Pt tandem photocathode can achieve a saturation photocurrent\ndensity of −30 mA/cm<sup>2</sup> at −0.9 V (vs RHE)\nand a photocurrent threshold voltage of −0.1 V for water reduction.\nThis work provides a silicon-based p-p-n heterojunction tandem structure\nfor the PEC water splitting; meanwhile, it indicates that PhC<sub>2</sub>Cu is a potential material to improve the stability of silicon-based\nPEC devices.