High carrier mobility along the [111] orientation in Cu2O photoelectrodes.
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Abstract
Solar fuels offer a promising approach to provide sustainable fuels by harnessing sunlight1,2. Following a decade of advancement, Cu2O photocathodes are capable of delivering a performance comparable to that of photoelectrodes with established photovoltaic materials3-5. However, considerable bulk charge carrier recombination that is poorly understood still limits further advances in performance6. Here we demonstrate performance of Cu2O photocathodes beyond the state-of-the-art by exploiting a new conceptual understanding of carrier recombination and transport in single-crystal Cu2O thin films. Using ambient liquid-phase epitaxy, we present a new method to grow single-crystal Cu2O samples with three crystal orientations. Broadband femtosecond transient reflection spectroscopy measurements were used to quantify anisotropic optoelectronic properties, through which the carrier mobility along the [111] direction was found to be an order of magnitude higher than those along other orientations. Driven by these findings, we developed a polycrystalline Cu2O photocathode with an extraordinarily pure (111) orientation and (111) terminating facets using a simple and low-cost method, which delivers 7 mA cm-2 current density (more than 70% improvement compared to that of state-of-the-art electrodeposited devices) at 0.5 V versus a reversible hydrogen electrode under air mass 1.5 G illumination, and stable operation over at least 120 h.
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Acknowledgements: The work was supported by funding from the European Research Council (ERC; HYPERION, grant 756962) and the Engineering and Physical Sciences Research Council (grant H2CAT, EP/V012932/1). L.P. acknowledges funding from the Swiss National Science Foundation under the Early Postdoc.Mobility fellowship (P2ELP2_195109). O.J.B. and S.H. acknowledge funding from the Engineering and Physical Sciences Research Council (EP/T001038/1). L.C. acknowledges funding from UK Research and Innovation-funded Postdoctoral Fellowships (Horizon Europe MSCA Postdoctoral Fellowships in the UK; EP/X022986/1). V.A. acknowledges financial support from St John’s College Cambridge (Title A Research Fellowship) and the Winton Programme for the Physics of Sustainability. A.A. acknowledges funding from the Royal Society. T.C.-J.Y acknowledges the support of the MSCA Individual Fellowship from the European Union’s Horizon 2020 (PeTSoC, No. 891205). E.R. was supported by an ERC Consolidator Grant (MatEnSAP, grant 682833) and a UK Research and Innovation–ERC Advanced Grant (EP/X030563/1). Y.Z. and H.S. acknowledge financial support from the EPSRC Centre for Doctoral Training in Graphene Technology, the Royal Society (RP/R1/201082) and the Engineering and Physical Sciences Research Council (EP/W017091/1). J.L. acknowledges funding from the National Natural Science Foundation of China (grant numbers 52072187 and 22122903) and the National Key Research and Development Program of China (grant number 2019YFE0123400). S.D.S. acknowledges the Royal Society and Tata Group (UF150033). We thank Y. Huang for assisting with the space-charge-limited current measurement, and Z. Liang for helping with the cross-sectional transmission electron microscopy imaging. For the purpose of open access, the authors have applied a Creative Commons Attribution (CC BY) licence to any author accepted manuscript version arising from this submission.
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1476-4687
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European Research Council (682833)
EPSRC (EP/T001038/1)
EPSRC (EP/V012932/1)
European Commission Horizon 2020 (H2020) Marie Sk?odowska-Curie actions (891205)
EPSRC (EP/W017091/1)