研究目的

The generation of hydrogen fuel by direct photoelectrochemical solar water splitting in a dual absorber tandem device offers a promising pathway for a sustainable future energy scenario. However, even though much progress has been made in the past decades, the commercialization potential of this approach is still unclear. One of the main bottlenecks is the identification of photoelectrode materials that are not only efficient, but also low-cost and stable on a time-scale of years. The best performing solar water splitting devices use high-quality III-V semiconductors, e.g., GaInP and GaInAs, as the top and bottom absorbers, respectively. These devices already show impressive solar-to-hydrogen (STH) efficiencies (up to 19%), but the long term stability and the high costs still prohibit practical applications. Other demonstrations are based on earth-abundant metal oxide photoelectrodes in combination with a Si-solar cell as a bottom absorber, or on combinations of two metal oxides in an all-oxide device. In general, these devices have the potential to be highly stable and low-cost, but the reported STH efficiencies have been modest thus far (~8%). This trade-off between efficiency, cost, and stability needs to be overcome in order to realize practical and scalable photoelectrochemical water splitting solutions.

研究成果

In summary, the study systematically investigated the structure, morphology, and charge carrier dynamics of pulsed laser-deposited α-SnWO4 films as a function of the deposition parameters and post-deposition annealing conditions. TRTS measurements revealed an upper limit for the combined electron-hole mobility of ~0.13?cm2?V-1?s-1, which is comparable to values reported for high efficiency BiVO4 photoelectrodes. The presence of grain boundaries significantly affects the carrier transport properties of α-SnWO4, with increasing crystallite domain size leading to a more than 10× higher photoconductivity measured by TRMC. The improvement does not saturate at 100 nm, suggesting that the photoconductivity of α-SnWO4 films can be further improved by growing films with larger domains/grains or even epitaxial films.

研究不足

The study identifies that the photoelectrochemical performance of PLD-deposited films is currently still limited by rapid surface passivation due to SnO2 formation (for unprotected α-SnWO4 films) or by trap states at the α-SnWO4/NiOx interface (for protected films). Additionally, the influence of the slight W-enrichment as well as the presence of small amounts of Sn4+ in the films on the charge carrier transport should be clarified.