Abstract
Oxysulfide semiconductor, Y2Ti2O5S2, has recently discovered its exciting potential for visible-light-induced overall water splitting, and therefore, imperatively requires the probing of unknown fundamental charge loss pathways to engineer the photoactivity enhancement. Herein, transient diffuse reflectance spectroscopy measurements are coupled with theoretical calculations to unveil the nanosecond to microsecond time range dynamics of the photogenerated charge carriers. In early nanosecond range, the pump-fluence-dependent decay dynamics of the absorption signal is originated from the bimolecular recombination of mobile charge carriers, in contrast, the power-law decay kinetics in late microsecond range is dominated by hole detrapping from exponential tail trap states of valence band. A well-calibrated theoretical model estimates various efficiency limiting material parameters like recombination rate constant, n-type doping density and tail-states parameters. Compared to metal oxides, longer effective carrier lifetime ~6 ns is demonstrated. Different design routes are proposed to realize efficiency beyond 10% for commercial solar-to-hydrogen production from oxysulfide photocatalysts.
Highlights
Oxysulfide semiconductor, Y2Ti2O5S2, has recently discovered its exciting potential for visible-light-induced overall water splitting, and imperatively requires the probing of unknown fundamental charge loss pathways to engineer the photoactivity enhancement
Transient diffuse reflectance spectroscopy (TDRS) is coupled with theoretical calculations to reveal the origin of distinct characteristics in the early nanosecond and late microsecond time range, respectively
Similar characteristics of X-ray diffraction (XRD) pattern and Diffuse reflectance spectroscopy (DRS) were recently reported by our group[24]
Summary
Transient diffuse reflectance spectroscopy (TDRS; Methods) measurements were performed to unravel the physical origin behind charge carrier dynamics of the Y2Ti2O5S2 photocatalyst. These features suggest band-to-band relaxation of charge carriers without irreversible trapping into deep trap levels within the time scale of measurement. As demonstrated in several previous studies[36,38,39,40], in transient absorption and reflectivity measurements, transient heating of the sample induced by the pump laser pulse can cause thermal components in the measured spectra and a proper assessment and isolation of its components are essential for accurate interpretation of photoinduced (nonthermal) electronic responses. SðtÞ 1⁄4 βΔn, the rate relation can be rearranged as dSðtÞ=dt 1⁄4 Àkrðneq þ Nt þ SðtÞ=βÞSðtÞ, which is solved to obtain SðtÞ as[41]
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