Sb₂Se₃ has emerged as a promising photocathode for water splitting owing to its high photoelectrochemical performance (~ 15 mAcm^-2) and resistance to photocorrosion in the absence of any protection layers.[1] It has been demonstrated that sulfurization treatment of Sb₂Se₃ improves the onset potential and hence the photovoltage. However, the origin of such an improvement in the photovoltage is not fully understood in the literature. In this work, we employ 2 techniques to understand this phenomenon. Firstly, by employing a novel dual working electrode technique where the surface potential could be sensed and this was used to determine the photovoltage. By in-situ surface potential sensing, the photovoltage was found to increase from 220 mV to 340 mV upon sulfurization treatment.  Next, from time-resolved microwave conductivity (TRMC), the carrier lifetimes and carrier mobilities were determined. Although the carrier mobilities remained the same, there was an increase in the carrier lifetime upon sulfurization treatment. Interestingly, this increase was more pronounced in shorter wavelengths (400-700 nm) than longer wavelength (700-1100nm) suggesting that the sulfurization treatment primarily reduces the surface recombination rather than bulk recombination. The carrier lifetimes obtained from Sb₂Se₃ were among the longest (in µs) in comparison to other emerging earth abundant materials like BiVO₄, CuFeO₂, CuWO₄ etc showing the immense potential of Sb₂Se₃ for photoelectrochemical water splitting applications.

[1] Rajiv Ramanujam Prabhakar,  Wilman Septina,  Sebastian Siol,  Thomas Moehl,  René Wick-Joliat  and  S. David Tilley  J.Mater. Chem. A, 2017,5, 23139-23145