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DTSTART;VALUE=DATE:20211109T111500
DTEND;VALUE=DATE:20211109T111500
UID:10398@agenda.unifr.ch
DESCRIPTION:Photocatalytic water splitting is one of the major routes towards sustainable energy\nconversion and storage based on hydrogen gas. The electrodes which absorb light from\nthe solar spectrum and finally inject carriers into the water are the key elements of the\nphotochemical cell [1].\nThe electrodes have to fulfill a number of requirements like large light absorption\ncoefficients, efficient carrier transport to the surface, and stability in aqueous\nenvironment. Cuprous oxide, Cu2O, is a prime candidate due to the small, direct\nbandgap of 2.1 eV and due to abundant and cheap constituents, but turned out to be\nunstable towards Cu reduction in contact with water. Moreover, even when capped with\nprotective layers, the photochemical conversion efficiencies are well below the\ntheoretically possible figures [2].\nUsing surface science techniques and, in particular time-resolved photoelectron\nspectroscopy, we studied the (111)-surface of Cu2O. Beside strong band bending at the\nsurface-vacuum interface [3] we found that the electron dynamics strongly depend on\nthe density of oxygen vacancies. In particular for the (√3x√3)R30° surface reconstruction\nwhich is indicative of the presence of an oxygen-deficient surface layer, the\nphotogenerated carriers are found to be trapped very efficiently [4]. Using density\nfunctional theory we investigated the electronic structure and in presence of various\ntypes of charged defects and computed the carrier capture coefficients [5].\nIn this talk I will present the experimental studies undertaken so far and compare the\noutcome with theoretical simulations. The latter yield strong evidence for charged\noxygen vacancies being responsible for the poor electrode efficiencies, and the capture\ncoefficients found are in agreement with trapping time scales obtained from the\nexperiments.\n[1] See e.g. https://www.lightchec.uzh.ch/en.html\n[2] W. Niu et al., Extended Light Harvesting with Dual Cu2O-Based Photocathodes for\nHigh Efficiency Water Splitting, Adv. Energy Mater. 8, 1702323 (2018).\n[3] D. Leuenberger et al., Atomically Resolved Band Bending Effects in a p-n\nHeterojunction of Cu2O and a Cobalt Macrocycle, Nano Lett. 17, 6620 (2017).\n[4] L. Grad et al., Influence of surface defect density on the ultrafast hot carrier relaxation\nand transport in Cu2O photoelectrodes, Sci. Rep. 10, 10686 (2020).\n[5] C. Ricca et al., Importance of surface oxygen vacancies for ultrafast hot carrier\nrelaxation and transport in Cu2O, submitted (2021); arXiv:2103.03167v2 [cond-mat.mtrlsci].
SUMMARY:Electron Dynamics and Defect Trapping in Cu2O(111)
CATEGORIES:Séminaire
LOCATION:PER 08\, 0.51\, Chemin du Musée 3\, 1700 Fribourg
URL;VALUE=URI:https://agenda.unifr.ch/e/fr/10398
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