Fullerene as a Photoelectron Transfer Promoter Enabling Stable TiO2-Protected Sb2Se3 Photocathodes for Photo-Electrochemical Water Splitting

Understanding the degradation mechanisms of photoelectrodes and improving their stability are essential for fully realizing solar-to-hydrogen conversion via photo-electrochemical (PEC) devices. Although amorphous TiO2 layers have been widely employed as a protective layer on top of p-type semiconductors to implement durable photocathodes, gradual photocurrent degradation is still unavoidable. This study elucidates the photocurrent degradation mechanisms of TiO2-protected Sb2Se3 photocathodes and proposes a novel interface-modification methodology in which fullerene (C-60) is introduced as a photoelectron transfer promoter for significantly enhancing long-term stability. It is demonstrated that the accumulation of photogenerated electrons at the surface of the TiO2 layer induces the reductive dissolution of TiO2, accompanied by photocurrent degradation. In addition, the insertion of the C-60 photoelectron transfer promoter at the Pt/TiO2 interface facilitates the rapid transfer of photogenerated electrons out of the TiO2 layer, thereby yielding enhanced stability. The Pt/C60/TiO2/Sb2Se3 device exhibits a high photocurrent density of 17 mA cm(-2) and outstanding stability over 10 h of operation, representing the best PEC performance and long-term stability compared with previously reported Sb2Se3-based photocathodes. This research not only provides in-depth understanding of the degradation mechanisms of TiO2-protected photocathodes, but also suggests a new direction to achieve durable photocathodes for photo-electrochemical water splitting.