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Author: search.filters.author.Francisco RumicheSubject: search.filters.subject.Surface states

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    Analysis of the physical and photoelectrochemical properties of c-Si(p)/a-SiC:H(p) photocathodes for solar water splitting
    (IOP Publishing Ltd, 2021-05-13)
    The photoelectrochemical (PEC) properties of sputtered aluminum doped hydrogenated amorphous silicon carbide thin films grown on p-type crystalline silicon substrates were investigated in 1 M H 2 S O 4 solution under chopped light illumination. Optical and structural properties of the top absorber layer were systematically assessed after post-deposition isochronical annealing treatments. Samples exhibited a noticeable improvement of the opto-electronic properties after thermal treatments. In addition, an abrupt enhancement of the photocurrent was observed reaching a saturation value of 17 mA cm −2 at −1.75 V vs. Ag/AgCl (3.5 M KCl). In this research we propose that this enhancement effect is associated to a charge transfer kinetic mechanism influenced by surface states and the p-type substrate. The latter most likely due to the space charge region extending beyond the absorber layer reaching the substrate. Current density-potential and electrochemical impedance spectroscopy measurements in dark revealed a reduction of the S i O 2 native layer at cathodic potentials higher than −1 V vs. Ag/AgCl (3.5 M KCl), which contributes to the high charge transfer kinetic of the system. We believe that these results will contribute to understand the substrate influence in the PEC performance of top absorber layers in multilayer structures for solar water splitting.
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    Localized surface states influence in the photoelectrocatalytic performance of Al doped a-SiC:H based photocathodes
    (Elsevier Ltd, 2022-06-01)
    In this work we evaluate the role of a-SiC:H(p)/SiO2 localized surface states (SS) in the Photoelectrochemical Water Splitting reaction. The analysis was carried out in three steps. First, retrieving the a-SiC:H(p) SS, energy distribution and density, by Electrochemical Impedance Spectroscopy techniques. Second, relating these results with direct measurements over the a-SiC:H(p)/SiO2 surface using X-ray Photoelectron spectroscopy. Finally, assessing the SS influence in the photo-induced hydrogen reduction by testing the a-SiC:H(p) photocathode with Linear Sweep Voltammetry. The whole analysis was done after subjecting the a-SiC:H(p) surface to different annealing treatments, i.e. 600 °C and 700 °C, necessary to obtain the required ohmic contacts. We believe that the participation of SS in an indirect electron charge transfer to the electrolyte, is kinetically feasible to take place in an a-SiC:H surface with relatively low SS density, ∼0.3×1012 cm-2. Whilst higher SS densities, in the range of ∼1.48×1014 cm-2, would trigger undesired charge carrier recombination.