Development of a Robust p-Si/p-Cu2O/PhC2Cu Tandem Photocathode for Photoelectrochemical Water Splitting

The photoelectrochemical (PEC) water splitting performance of Si-based PEC devices is usually restricted by low stability and weak photogenerated carrier transport ability. Herein, a micropyramid array structure (p-SiMPs)/p-Cu₂O/PhC₂Cu/Pt photocathode device with a p-p-n heterojunction structure is developed. In this tandem PEC device, a p-p heterojunction of p-SiMPs/p-Cu₂O is achieved, endowing a higher interface electric field and stronger energy of photoinduced electrons for PEC water reduction. In addition, a stable n-type PhC₂Cu protective layer is prepared on the surface of the PEC device by the photoassisted polymerization method, which can improve the stability of PEC water reduction largely. After Pt cocatalytic layer deposition, the p-SiMPs/p-Cu₂O/PhC₂Cu/Pt tandem photocathode can achieve a saturation photocurrent density of −30 mA/cm² at −0.9 V (vs RHE) and a photocurrent threshold voltage of −0.1 V for water reduction. This work provides a silicon-based p-p-n heterojunction tandem structure for the PEC water splitting; meanwhile, it indicates that PhC₂Cu is a potential material to improve the stability of silicon-based PEC devices.