SKM 2023 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 47: Oxide Semiconductors II

HL 47.7: Talk

Friday, March 31, 2023, 11:15–11:30, POT 81

Charge carrier diffusion and localization in metal oxide photoabsorbers — •Hannes Hempel, Markus Schleuning, Klaus Schwarzburg, Rainer Eichberger, Roel van de Krol, Moritz Kölbach, Fatwa F. Abdi, and Dennis Friedrich — Helmholtz-Zentrum Berlin, Germany

Long diffusion lengths of photo-excited charge carriers are crucial for high power conversion efficiencies of photoelectrochemical and photovoltaic devices. However, in metal oxids are effects such as (multiple-)trapping, carrier localization and polaron formation can lead to time-varying mobilities and lifetimes that are not accounted for in the conventional analysis. Therefore, here, a generalized analysis is presented that determines the diffusion length directly from the integral of a photoconductivity transient, regardless of the nature of carrier relaxation. This approach is presented on amorphous silicon, a prototype of disordered materials, and BiVO4, one of the most studied photoanode materials for solar water splitting. Our generalized analysis allows monitoring the temporal evolution of the charge carrier displacement, which converges for both materials after ~100 ns to a diffusion length of a few tens of nanometers. For BiVO4, the obtained diffusion length is significantly shorter than the typical thin film thickness, which rationalizes the photocurrent loss in the corresponding photoelectrochemical device. Finally, we probe several metal other prominent metal oxide photoabsorbers, namely Fe2O3, FeVO4, CuFeO2, α-SnWO4, BaSnO3, and CuBi2O4, and find sings of carrier localization on the nanometer scale, which limits the charge carrier diffusion.