Vertical nanosheet-structured ZnO/TiO2 photoelectrodes for highly efficient CdS quantum dot sensitized solar cells

• The vertical ZnO/TiO2 nanosheet-structured films were prepared by a feasible deposition processes.
• The photo-excited electron lifetimes in the photoanode were significantly improved.
• A high power conversion efficiency of 1.95% was obtained for the CdS quantum dots sensitized solar cells.

Employing vertical nanosheet-structured films as photoanodes of quantum dot sensitized solar cells (QDSCs) might provide a direct pathway for the photo-exited electrons. Here, the vertical ZnO, ZnO/TiO2 and TiO2 nanosheet-structured films were prepared by a feasible deposition processes. These films were sensitized with CdS quantum dots and assembled with CuS counter electrodes to fabricate QDSCs. The photoelectric properties of ZnO/TiO2 composite films were superior to both pure ZnO and TiO2 films. The effects of TiO2 coating were investigated using electrochemical impedance spectroscopy (EIS). It was found that the photo-excited electron lifetimes in the photoanode were significantly improved with TiO2 layer. The optimum power conversion efficiency was about 1.95% under AM 1.5 G illumination (100 mW cm−2), with a short circuit current density, open circuit voltage, and fill factor of 6.11 mA cm−2, 0.562 V and 0.57, respectively.