Analysis of charge trapping and long lived hole generation in SrTiO3 photoanodes

Abstract

Charge carrier dynamics studies of SrTiO₃ under applied bias offer the opportunity to gain unique insights into what underpins its state-of-the-art photocatalytic water splitting activity. Herein, time resolved spectroscopic measurements are employed, to investigate the impact of applied bias on the transient and steady state charge carrier dynamics of SrTiO₃ across μs–s timescales, and simultaneously measure charge extraction kinetics. A high density of Ti³⁺ defect states in SrTiO₃ photoanodes are identified and associated with prevalent electron trapping into deep states, which is in competition with electron extraction and limits the photocurrent. Despite the high density of trapped electrons, an intrinsically long lifetime for photogenerated holes in SrTiO₃ photoanodes is observed using transient absorption spectroscopy, even in the absence of applied bias. This is important for overcoming the slow kinetics and hole accumulation associated with the water oxidation reaction, and for enabling good performance in photocatalytic systems where bias cannot be applied.