Oligo(poly)thiophene Sensitization of CdSe Nanocrystal and TiO2 Polycrystalline Electrodes: A Photoelectrochemical Investigation

Oligo(poly)thiophenes were investigated by photoelectrochemical methods as monolayer sensitizers of CdSe nanocrystal (CdSe-NCs) and TiO2 polycrystalline films on ITO electrodes. 7.5 nm diameter CdSe-NCs layers and polycrystalline (anatase, ca. 40 nm crystallite size) TiO2 films were functionalized with an alpha,omega-dicarboxylic sexithiophene and with two polythiophenes, bearing differently spaced side carboxylic terminals, including regioregular poly(thiophene-3-propionic acid). The modified electrodes were investigated in a three-electrode photoelectrochemical cell in the presence of iodide as sacrificial generator of intense and steady oxidative photocurrents. The oligo(poly)thiophenes act in general as moderate hypersensitizers (roughly twice more efficient than calculated). Poly(thiophene-3-propionic acid) monolayers, formed on CdSe-NC structures from ethanol, generate a strong hypersensitization, i.e., a response 5 times higher than expected. From optical and photoluminescence analysis such a result is attributed to a flat disposition of the thiophene planes on the surface which allows a faster phototransport. CdSe-NC sensitization of the ITO and TiO2 surfaces is also reported in detail.