High-Efficiency Dye-Sensitized Solar Cells Based on a ZnO Nanorod/ Nanosheet Hierarchical Structure

Abstract

Aqueous solution of Zn(NO₃)₂*6H₂O-C₆H₂N₄-PEI and Zn(NO₃)₂*6H₂O-CO(NH₂)₂ were used as raw materials to fabricate hierarchically structured films of ZnO nanorods/nanosheets (ZnO NRs/NSs) via a two-step hydrothermal synthesis, and the films of ZnO NRs/NSs were applied as photoanodes for application in dye-sensitized solar cells (DSSCs). Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were utilized to characterize the morphologies of the ZnO films. The current density-voltage curves and the incident monochromatic photon-to-electron conversion efficiency of DSSCs were measured. Through electrochemical impedance spectroscopy, intensity modulated photovoltage spectroscopy , and intensity modulated photocurrent spectroscopy, the conditions of the internal electron transport and transfer of ZnO-based DSSCs were tested and analyzed. The results indicate that the ZnO NRs/NSs photoanodes not only have properties of rapid electron transport and high electron collection efficiency but also show a relatively large amount of dye absorption. Therefore, for DSSCs based on ZnO NRs/NSs, the short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), and photoelectric conversion efficiency (PCE) were 11.82 mA cm-2, 0.66 V, 0.58, and 4.59%, respectively. The PCE of the DSSCs was improved by 178.18% with respect to that of pure ZnO NRs cells (1.65%) and was improved by 21.42% with respect to the pure ZnO NSs cells (3.78%).