ZnO/TiO2 core-shell heterojunction for CdS and PbS quantum dot-cosensitized solar cells

ZnO nanorods (NRs) with regular morphology were prepared through hydrothermal method, and the TiO2 shell was assembled onto the surface of ZnO NRs by spin coating to the ZnO/TiO2 core-shell heterojunction. CdS and PbS quantum dots (QDs) were used to cosensitize the ZnO/TiO2 nanostructure by direct adsorption (DA) and successive ionic layer adsorption and reaction, respectively. SEM, TEM, and HRTEM images show that the samples possessed a rough surface and four lattice fringes indicating the successful synthesis of the ZnO/TiO2/CdS/PbS composite structure. The ZnO/TiO2(10T)/CdS/PbS sample showed a high absorption intensity at a broad range of wavelength to visible light region. The ZnO/TiO2(10T)/CdS/PbS photoelectrode with QDSSCs showed the highest IPCE of 36.04% and photoelectric efficiency (η) of 1.59%; these values increased by approximately 550% and 150% compared with those of unsensitized ZnO (0.29%) and ZnO/TiO2(10T) (1.04%) and about 146% and 120% compared with those of ZnO/TiO2(10T)/CdS and ZnO/TiO2(10T)/PbS, respectively. The fill factor was 0.36, and the photocurrent density (Jsc) and open circuit voltage (Voc) reached the maximum values of 9.73 mA cm−2 and 0.46 V, respectively.