Proceedings of MATSUS Spring 2024 Conference (MATSUS24)
DOI: https://doi.org/10.29363/nanoge.matsus.2024.174
Publication date: 18th December 2023
Metal oxide photoelectrodes tend to be cheap, easy to fabricate, and show relatively good (photo)chemical stability in aqueous solutions. This makes them attractive candidates as light absorbers in a variety of photoelectrochemical and photocatalytic applications. However, the efficiencies of these absorbers are poor compared to photovoltaic-grade materials. This is usually attributed to polaron formation and recombination or trapping at defects. To determine the quality of metal oxide absorbers, time-resolved photoconductance measurements are often used as a convenient and contact-free method to determine the carrier diffusion length. Here, one of the main challenges is to determine whether the decay in photoconductivity is due to a decay in carrier concentration (recombination), a decay in carrier mobility (trapping, polaron formation), or both. I will present a general analysis method for determining the diffusion length which is valid for time-dependent mobilities as well as time-dependent lifetimes [1]. We have applied this method to a range of metal oxides and validated the method by applying it also to crystalline silicon and a halide perovskite. We find a carrier diffusion length of only 15 nm for BiVO4, which is significantly shorter than previously reported values by us and others. I will discuss how this value can be reconciled with the relatively high photocurrents that many groups have reported for this material. For several other oxides that we studied, we find evidence for nm-scale carrier localization [2], which is likely due to nano-sized crystallites or defect clusters. Mitigation of this strong localization may be possible and would offer a promising strategy for designing more efficient metal oxide-based photoelectrodes.
This work was carried out within the Helmholtz International Research School “Hybrid Integrated Systems for Conversion of Solar Energy” (HI-SCORE), an initiative co-funded by the Initiative and Networking Fund of the Helmholtz Association (HIRS-0008).
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