Identifying Performance-Limiting Deep Traps in Ta₃N₅ for Solar Water Splitting

Abstract

Ta3N5 is a promising semiconductor for solar-driven photocatalytic or photoelectrochemical (PEC) water splitting. However, the lack of an in-depth understanding of its intrinsic defect properties limits further improvement of its performance. In this study, comprehensive spectroscopic characterizations are combined with theoretical calculations to investigate the defect properties of Ta3N5. The obtained electronic structure of Ta3N5 reveals that oxygen impurities are shallow donors, while nitrogen vacancies and reduced Ta centers (Ta3+) are deep traps. The Ta3+ defects are identified to be most detrimental to the water splitting performance because their energetic position lies below the water reduction potential. Based on these findings, a simple H2O2 pretreatment method is employed to improve the PEC performance of the Ta3N5 photoanode by reducing the concentration of Ta3+ defects, resulting in a high solar-to-hydrogen conversion efficiency of 2.25%. The fundamental knowledge about the defect properties of Ta3N5 could serve as a guideline for developing more efficient photoanodes and photocatalysts.

Recent Developments in Visible‐Light‐Absorbing Semitransparent Photoanodes for Tandem Cells Driving Solar Water Splitting

“…Fu et al proposed that Ta 3+ was the most detrimental to the water‐splitting performance of Ta 3 N 5 . [ 92 ] The authors used low‐temperature photoluminescence (PL) spectroscopy to evaluate the effect of deep trap states. They assigned a peak in PL spectra at 730 nm to V N and the other peak at 830 nm to Ta 3+ by the difference of NH 3 flow rate dependence.…”

“…c) Schematic diagram of the energetic structure of Ta 3 N 5 with O N , V N , and Ta 3þ defects. Reproduced with permission [92]. Copyright 2020, American Chemical Society.…”

A Review of Inorganic Photoelectrode Developments and Reactor Scale‐Up Challenges for Solar Hydrogen Production

“…In addition, Li and co‐workers have suggested that the presence of deep hole traps, arising from the presence of N vacancies, may also contribute to this process. [ 239 ] Current work on Ta 3 N 5 therefore is focused on surmounting the twin challenges of stability and relatively late onset potential.…”

Identifying Reactive Sites and Surface Traps in Chalcopyrite Photocathodes

“…Several studies have ascribed this signal to the transition from the conduction band edge ( E CB ) to shallow acceptor levels that lie near the valence band edge ( E VB ) [24, 26, 27] . Figure 2 c shows an estimate of the energy band positions including the location of the traps [28] . Figures 2 a,b displays the PL spectrum in terms of potential for the sake of comparison with LSVs (Figure S10).…”