9 December 1992 Redox chemistry at Si and TiO2 semiconductor materials
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Very sensitive near infrared (NIR) emission and visible/NIR cw dye laser based transient absorption techniques are employed to explore elementary steps of redox reactions at semiconductor materials. The focus is on chemistry relevant to the conversion of abundant long wavelength solar photons (red and NIR) into electricity in photoelectrochemical cells. Direct reduction of excited O2(1(Delta) ), a long-lived NIR energy carrier, has been demonstrated at a silicon electrode, opening up the possibility of direct conversion of the chemically stored 1 eV quantum of O2(1(Delta) ) into electrical energy in a singlet O2 driven regenerative cell. In a parallel direction, the rise of the one electron oxidation intermediate I2- produced upon photo-oxidation of iodide at dye sensitized as well as bare TiO2 colloidal particles has been observed for the first time by monitoring the 2(pi) g $IMP 2(Sigma) u+ absorption in the 700 - 800 nm region. Elucidation of the detailed steps of halide-to-halogen oxidation at the semiconductor/solution interface is important for progress in NIR photon energy storage and conversion as the intrinsically modest driving forces of such processes require careful optimization of the efficiency of each reaction step.
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Heinz Frei, Heinz Frei, } "Redox chemistry at Si and TiO2 semiconductor materials", Proc. SPIE 1729, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XI: Photovoltaics, Photochemistry, Photoelectrochemistry, (9 December 1992); doi: 10.1117/12.130583; https://doi.org/10.1117/12.130583

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