Rational design of surface passivation for highly efficient quantum dot sensitized solar cell

Surface passivation of quantum dot sensitized photoanode is of significant importance to enhance the performance of quantum dot sensitized solar cell (QDSSC) by reducing the charge recombination at photoanode/electrolyte interface. In this paper, we report a rational way to design an efficient surface passivation to enhance the cell performance of QDSSC, based on the systematic study of the influence of the structure and properties of overcoating layers on the performance of QDSSC. CdSe/TiO2 prepared from a postsynthesis assembly approach was used as the photoanode film, while ZnS and ZnSe were used as the passivation materials to be deposited on CdSe/TiO2 via a successive ionic layer adsorption and reaction (SILAR) route. Investigations showed that, QDSSC overcoated with ZnS/ZnSe dual passivation layer strongly inhibited the charge recombination and thus achieved high power conversion efficiency of 6.83%, much higher than the cells without or with single ZnS or ZnSe overcoating as well as the dual passivation with reversed deposition sequence. Detailed analyses demonstrate that passivation of overcoating is closely related to the coverage of QDs on TiO2, the lattice parameters and band structure of QD, TiO2 and overcoating materials, and a rational design of the surface overcoating is crucial for enhancing the cell performance of QDSSC.