Improving the efficiency of quantum-dot-sensitized solar cells by optimizing the growth time of the CuS counter electrode

Abstract

CuS counter electrodes (CEs) were prepared to fabricate efficient quantum-dot-sensitized solar cells (QDSSCs) based on a CdS/CdSe photo sensitizer. The CEs were prepared on a fluorine-doped tin oxide (FTO) glass substrate by a facile chemical bath deposition (CBD) method by dissolving CuSO4·5H2O and CH3CSNH2 in water, followed by adding 0.25mM polyvinylpyrrolidone (PVP). The CBD was performed at 60°C for 1h, 2h, and 3h, and the samples were labeled as CuS 1h, CuS 2h, and CuS 3h, respectively. The QDSSCs were assembled using prepared CuS CEs and a TiO2/CdS/CdSe/ZnS photoanode, and the effect of the growth time of CuS CEs on the QDSSC performance was investigated. As the CuS growth time increases, the short-circuit current density (Jsc), fill factor (FF), and open-circuit voltage (Voc) of the QDSSCs gradually increases, leading to an enhanced power conversion efficiency (η). QDSSCs that use the CuS 2h CE exhibit a high Jsc of 14.31mAcm−2, Voc of 0.603V, and FF of 0.49, which are higher than that using conventional Pt electrodes as well as CuS 1h and CuS 3h electrodes. The electrochemical impedance spectroscopy results show that the CuS 2h CE exhibits an inferior charge transfer resistance of only 2.93Ω, which is 33 times lesser than that of the Pt CE. The enhanced device performance of CuS 2h is ascribed to the high catalytic activity and low charge transfer resistance of the CuS CE in the reduction process of oxidized polysulfide. Consequently, a superior power conversion efficiency of 4.27% is achieved for QDSSCs utilizing CuS 2h.