Improving charge separation of solar cells by the co-sensitization of CdS quantum dots and dye

A co-sensitizer of CdS quantum dots plus N3 dye was developed to improve the conversion efficiency of solar cells. The photoanode of the solar cells was composed of ZnO nanowires coated with the CdS quantum dots and N3 dye successively; such a constructor can not only overcome the photocorrosion of CdS quantum dots, but also decrease the dissolution of ZnO nanowires, especially, improving the charge separation and electron injection. The open-circuit voltage of co-sensitized solar cells is also improved due to an enhanced retardation of charge recombination. The conversion efficiency of solar cells is enhanced from 0.5% of N3 sensitizer and 0.4% of CdS quantum dots to 1.9% of co-sensitizer; the significant improvement is attributed to the efficient hole transfer from CdS to N3 dye, which eliminates the exciton annihilation process and allows a leisurely electron injection into ZnO nanowires. Our result indicates that the co-sensitization is an essential step for highly efficient solar cell operation