Enhanced Performance of CdS/CdSe Quantum Dot Cosensitized Solar Cells via Homogeneous Distribution of Quantum Dots in TiO2 Film

The thickness and porosity of TiO2 mesoporous film were optimized for better distribution of quantum dots to enhance the performance of CdS/CdSe quantum dot cosensitized solar cells. The CdS and CdSe quantum dots were prepared on TiO2 mesoporous film through a successive ion layer absorption and reaction (SILAR) method and a chemical bath deposition (CBD) method, respectively. It was found that the distribution of quantum dots was inhomogeneous from the surface to the interior of the TiO2 film, being mainly concentrated at the upper layer of the TiO2 film. As a result, simply increasing film thickness did not make significant contribution to improving solar cell efficiency since only a small portion of quantum dots might access the interior of the film, leading to an exposure of TiO2 nanoparticles in electrolyte and thus reducing the electron lifetime due to increased charge recombination rate. Our study revealed that the efficiency could reach its maximum, similar to 4.62%, with the TiO2 film, the thickness of which was around 11 mu m, and porosity was optimized by adding 12 wt % ethyl cellulose into the paste for making the TiO2 film.