Further Improvement in Efficiency of ZnO Nanorod Based Solar Cells Using ZnS Quantum Dots as Light Harvester and Blocking Layer Material

Zinc oxide nanorod arrays (ZnO NRs) were grown on the ZnO seed layers via an aqueous solution using hydrothermal method and their photovoltaic properties were investigated. It was found that the growth period of 20 minutes is the optimum condition for ZnO nanorods growth, the cell containing these nanorods was considered as a reference cell. In order to further increase the cell performance, ZnS quantum dots (QDs) were fabricated on the ZnO NRs (reference cell) by SILAR technique with different number of cycles. The effect of the number of SILAR cycle (n) on structural and photovoltaic properties was studied. The optimum number of SILAR cycles for ZnS QDs was obtained (n=4). Experimental results showed that using ZnS QDs as light absorber material is an effective way to improve device performance. Morphology, crystalline structure and optical absorption of layers were analyzed by a scanning electron microscope (SEM), X-ray diffraction (XRD) and UV-Visible absorption spectra, respectively. The maximum power conversion efficiency of 3.59% in the inverted configuration of ITO/ZnO film/ZnO NR(20)/ZnS(n) QDs/P3HT/PCBM/Ag hybrid solar cell was achieved for a device based on ZnS(4) under an illumination of one Sun (AM 1.5G, 100 mW/cm2).