Fumed SiO2 modified electrolytes for quantum dot sensitized solar cells with efficiency exceeding 11% and better stability

For quantum dot sensitized solar cells (QDSCs), optimizing interfacial structures by specifically developing new interfacial modification methods to minimize recombination associated with photo-generated carrier transportation and collection is an effective way to achieve highly efficient devices. In this respect, fumed SiO2 nanoparticles have been used as a polysulfide electrolyte additive for improving the interface in a TiO2/QDs/electrolyte for the first time. It was found that the fill factor (FF), open-circuit voltage (V-oc) and the cell performance of the devices are significantly enhanced. Additionally, a power conversion efficiency (PCE) of 11.23% is achieved, which is one of the highest efficiencies for liquid-junction QDSCs. Furthermore, the electron transport and recombination processes in the CdSexTe1-x QDSCs with the SiO2 modified electrolyte have been investigated. This revealed that the existence of SiO2 nanoparticles in the electrolyte can create an energy barrier for the recombination between photo-generated electrons from the QDs as well as the recombination between the electrolyte and the injected electrons from TiO2. It is encouraging that CdSexTe1-x QDSCs in SiO2 modified electrolytes can reach a higher electron collection efficiency (98%) and longer electron lifetime. This work provides a simple and convenient method to modify the TiO2/QDs/electrolyte interfaces of QDSCs.