A novel Yb3+/Tm3+ co-doped semiconductor sensitized up-conversion strategy for β-In2S3 photoanode with enhanced photoelectrochemical properties

Abstract

N-type β-Indium sulfide (β-In2S3) has emerged as one of the most promising semiconductor photoanode for use in photoelectrochemical water-splitting in recent years, its defective spinel structure facilitates the incorporation of foreign ions to adjust the photoelectrochemical (PEC) performance. Lanthanide ions with excellent optical properties and abundant energy level structure have attracted much attention. In this study, the semiconductor sensitized up-conversion strategy was first applied to improve the PEC performance of β-In2S3 by inhibiting electron-hole pairs recombination. Yb3+/Tm3+ co-doped β-In2S3 (YTS) were successfully prepared on FTO substrate in-situ as PEC water splitting photoanode by a simple hydrothermal method, the effects of Yb3+/Tm3+ co-doping on PEC properties, charge-transport properties and energy band structure are discussed. When Yb3+ ions in the total cations of precursor accounted for 3%, and Tm3+ ions accounted for 0.5%, the photocurrent density of Yb3+/Tm3+ co-doped β-In2S3 (YTS-3) is 0.42 mA/cm2 (0.5 V vs. Ag/AgCl), which is about 1.68 times higher than pure β-In2S3 (0.25 mA/cm2). No photocurrent response was detected under 980 nm single-wavelength LED, proving that host material sensitization is more effective than direct excitation. The improved PEC properties for Yb3+/Tm3+ co-doped β-In2S3 might be attributed to the semiconductor sensitized up-conversion strategy, which realize a cycle of energy released by electron-hole pairs recombination. Moreover, the donor states formed after doping inhibits the recombination of electron-hole pairs by capturing electrons. The ways that the Yb3+/Tm3+ dopants modified the energy band structure and PEC properties of β-In2S3 demonstrated in this study have guiding significance for the design of lanthanide ions doped semiconductor photoanode.