Self-Assembled Structures of Semiconductor Nanocrystals and Polymers for Photovoltaics. 1. CdSe Nanocrystal-Polymer Multilayers. Optical, Electrochemical, Photoelectrochemical and Photoconductive Properties

Hybrid materials of polymers and cadmium selenide nanocrystals (CdSe-NCs) were produced through a layer-by-layer deposition technique. Polymer series comprises sulfonic, phosphonic and carboxylic acids, pyridine- and amine-based polymers and some related bipolar amphiphiles including a dithiol. Nonaqueous dispersions of amine- and oleate-capped CdSe-NCs with 3, 4 and 5 nm diameter were used. Polymers and CdSe-NCs are alternately deposited on indium-tin-oxide/glass surfaces. CdSe-NCs layers undergo a sharp and irreversible electroxidation process in acetonitrile corresponding to the passage of two electrons per CdSe unit. The multilayer build-up, monitored by UV-vis spectroscopy and cyclic voltammetry, shows an increase of the film absorbance and oxidation stripping charge proportional with the number of adsorbed CdSe layers and with the particle diameter. Layer formation rate by acids follows their acidity, with thiols being much slower than sulfonic, phosphonic or carboxylic acids. The semiconductor properties of the multilayers were evidenced by photoluminescence (PL), photoelectrolchemical and photoconduction analysis. Good PL was recorded in pyridine-, amine- and carboxylate-based multilayers, PL quenching in sulfonate-, phosphonate- and thiolate-based multilayers. PL quenching is accompanied by higher photoelectrochemical and photoconductivity responses.