Interfacial modification of photoelectrode in ZnO-based dye-sensitized solar cells and its efficiency improvement mechanism

Abstract

A ZnO compact layer prepared by a sol–gel method was introduced into a photoelectrode at the interface between fluorine-doped tin oxide (FTO) substrate and a mesoporous ZnO layer in ZnO-based dye-sensitized solar cells (DSSCs). The ZnO compact layer was characterized by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and UV-Vis spectroscopy. The compact layer increased the photoelectric conversion efficiency of ZnO-based DSSCs by 20%. An electrochemical impedance spectroscopy (EIS) study demonstrated that the compact layer strikingly reduced the interfacial resistance in the device by enhancing the conductive contact between nanocrystalline ZnO and FTO substrate. The photocurrent density–voltage characteristics in the dark suggests that the compact ZnO layer also plays the role of a blocking layer suppressing the charge recombination, which is illustrated by the suppression of dark current density. The two effects effectively elevate the short circuit current density (J_SC) and open circuit voltage (V_OC), and finally improve the overall conversion efficiency of ZnO-based DSSCs.