Interface Passivation Effects on the Photovoltaic Performance of Quantum Dot Sensitized Inverse Opal TiO(2) Solar Cells

Quantum dot (QD)-sensitized solar cells (QDSSCs) are expected to achieve higher energy conversion efficiency than traditional single-junction silicon solar cells due to the unique properties of QDs. An inverse opal (IO)-TiO(2) (IO-TiO(2)) electrode is useful for QDSSCs because of its three-dimensional (3D) periodic nanostructures and better electrolyte penetration compared to the normal nanoparticles (NPs)-TiO(2) (NPs-TiO(2)) electrode. We find that the open-circuit voltages V(oc) of the QDSSCs with IO-TiO(2) electrodes are higher than those of QDSSCs with NPs-TiO(2) electrodes. One important strategy for enhancing photovoltaic conversion efficiency of QDSSCs with IO-TiO(2) electrodes is surface passivation of photoanodes using wide-bandgap semiconducting materials. In this study, we have proposed surface passivation on IO-TiO(2) with ZnS coating before QD deposition. The efficiency of QDSSCs with IO-TiO(2) electrodes is largely improved (from 0.74% to 1.33%) because of the enhancements of V(oc) (from 0.65 V to 0.74 V) and fill factor (FF) (from 0.37 to 0.63). This result indicates that ZnS passivation can reduce the interfacial recombination at the IO-TiO(2)/QDs and IO-TiO(2)/electrolyte interfaces, for which two possible explanations can be considered. One is the decrease of recombination at IO-TiO(2)/electrolyte interfaces, and the other one is the reduction of the back-electron injection from the TiO(2) electrode to QDs. All of the above results are effective for improving the photovoltaic properties of QDSSCs.