Solar cells based on a mesoporous structure of TiO2 and the polysulfide redox electrolyte were prepared by direct adsorption of colloidal CdSe quantum dot light absorbers onto the oxide without any particular linker. Several factors cooperate to improve the performance of quantum-dot-sensitized solar cells: an open structure of the wide bandgap electron collector, which facilitates a higher covering of the internal surface with the sensitizer, a surface passivation of TiO2 to reduce recombination and improved counter electrode materials. As a result, solar cells of 1.83% efficiency under full 1 sun illumination intensity have been obtained. Despite a relatively large short circuit current (J(sc) = 7.13 mA cm(-2)) and open circuit voltage (V(oc) = 0.53 V), the colloidal quantum dot solar cell performance is still limited by a low fill factor of 0.50, which is believed to arise from charge transfer of photogenerated electrons to the aqueous electrolyte.

Colloidal CdSe quantum dots (QDs) of different sizes, prepared by a solvothermal route, have been employed as sensitizers of nanostructured TiO(2) electrode based solar cells. Three different bifunctional linker molecules have been used to attach colloidal QDs to the TiO(2) surface: mercaptopropionic acid (MPA), thioglycolic acid (TGA), and cysteine. The linker molecule plays a determinant role in the solar cell performance, as illustrated by the fact that the incident photon to charge carrier generation efficiency (IPCE) could be improved by a factor of 5-6 by using cysteine with respect to MPA. The photovoltaic properties of QD sensitized electrodes have been characterized for both three-electrode and closed two-electrode solar cell configurations. For three-electrode measurement a maximum power conversion efficiency near 1% can be deduced, but this efficiency is halved in the closed cell configuration mainly due to the decrease of the fill factor (FF).