Self-Assembled Structures of Semiconductor Nanocrystals and Polymers for Photovoltaics. (3) PbSe Nanocrystal-Polymer LBL Multilayers. Optical, Electrochemical, Photoelectrochemical, and Photoconductive Properties

Hybrid materials of lead selenide nanocrystals (PbSe-NCs) and organic polymers were produced through a layer-by-layer (LBL) solution-based deposition technique. Polymer series comprises sulfonate-, carboxylate-, and pyridine-based polymers. Nonaqueous dispersions of oleate-capped PbSe-NCs with 2.4 or 2.8 nm diameter were used. Polymers and PbSe-NCs are alternately deposited on ITO-glass surfaces. PbSe-NCs layers in acetonitrile undergo a sharp and irreversible electroxidation process involving two electrons per PbSe unit and an irreversible reduction process due to reduction of a surface lead(II) shell, which involves 20% of the oxidation charge. The multilayer build-up, monitored by UV-vis spectroscopy and cyclic voltammetry, proceeds with a linear increase in the film absorbance and oxidation stripping charge with the number of adsorbed PbSe layers. FTIR analysis has shown that the layering polymers remove the oleate capping ligands completely. The semiconductor properties of these LBL films were evidenced by photoelectrolchemical and (photo)conduction analysis. Photoelectrochemical (oxygen reduction) and photoconductivity responses are stronger in pyridine- than in carboxylate- and sulfonate-based multilayers, suggesting the occurrence of an efficient trapping of the surface lead(II) shell by pyridine moieties.