Investigation of Coral-Like Cu2O Nano/Microstructures as Counter Electrodes for Dye-Sensitized Solar Cells

In this study, a chemical oxidation method was employed to fabricate coral-like Cu2O nano/microstructures on Cu foils as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). The Cu2O nano/microstructures were prepared at various sintering temperatures (400, 500, 600 and 700 °C) to investigate the influences of the sintering temperature on the DSSC characteristics. First, the Cu foil substrates were immersed in an aqueous solution containing (NH4)2S2O8 and NaOH. After reacting at 25 °C for 30 min, the Cu substrates were converted to Cu(OH)2 nanostructures. Subsequently, the nanostructures were subjected to nitrogen sintering, leading to Cu(OH)2 being dehydrated into CuO, which was then deoxidized to form coral-like Cu2O nano/microstructures. The material properties of the Cu2O CEs were comprehensively determined using a scanning electron microscope, energy dispersive X-ray spectrometer, X-ray diffractometer, Raman spectrometer, X-ray photoelectron spectroscope, and cyclic voltameter. The Cu2O CEs sintered at various temperatures were used in DSSC devices and analyzed according to the current density-voltage characteristics, incident photon-to-current conversion efficiency, and electrochemical impedance characteristics. The Cu2O CEs sintered at 600 °C exhibited the optimal electrode properties and DSSC performance, yielding a power conversion efficiency of 3.62%. The Cu2O CEs fabricated on Cu foil were generally mechanically flexible and could therefore be applied to flexible DSSCs.