Factors determining the photovoltaic performance of a CdSe quantum dot sensitized solar cell:: the role of the linker molecule and of the counter electrode

Colloidal CdSe quantum dots (QDs) of different sizes, prepared by a solvothermal route, have been employed as sensitizers of nanostructured TiO2 electrode based solar cells. Three different bifunctional linker molecules have been used to attach colloidal QDs to the TiO2 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).