Improving loading of CdS/CdSe co-sensitized quantum dots to enhance the performance of solar cells by voltage-assisted SILAR deposition

In the conventional successive ionic layer adsorption and reaction (SILAR), the slow growth and uneven distribution of quantum dots (QDs) in TiO2 mesoporous films limit the loading amount of QDs, decreasing the effectiveness of QDs to improve quantum dot-sensitized solar cells (QDSSCs). Especially in CdS/CdSe cosensitized solar cells, the growth of CdS QDs on the surface of TiO2 films blocks the internal voids, making it difficult to load the post-sequence CdSe into the interior of the TiO2 mesoporous films. Herein, we have developed a simple and rapid voltage-assisted SILAR technique (VASILAR) to load CdS/CdSe QDs into the TiO2 mesoporous films more efficiently. Comparing with conventional SILAR method, the electric field generated by imposing the voltage could drive the ions to diffuse/penetrate rapidly into the interior of the mesoporous films, promoting the preferential deposition of a large number of CdS in the deep region of the films. A uniform distribution of CdS in TiO2 mesoporous films is achieved. The uniform distribution of CdS leaves sufficient space and channels for the loading of the post-sequence CdSe inside the films. Further with the help of electric field forces, the growth and distribution of CdSe in the film are also well regulated. Finally, the rapid growth and uniform distribution of CdS/CdSe co-sensitized QDs in TiO2 mesoporous films as well as a high loading amount of QDs are attained. The resulting CdS/CdSe co-sensitized QDSSCs exhibits an outstanding efficiency of 5.7%, and a remarkable stability after over 660 min.