Three-dimensional graphitic C3N4/CuS composite as the low-cost and high performance counter electrodes in QDSCs

Abstract

As an essential working part in quantum dots sensitized solar cells (QDSCs), the counter electrode (CE) performs the function of extracting electrons form external circuit and catalyzing the reduction of electrolyte. To improve photovoltaic performance of cells, a new novel composite CE composed of graphitic C3N4 (g-C3N4) nanosheets and CuS nanoparticles is prepared on FTO glass via chemical bath deposition method. CuS nanoparticles can be successfully deposited on g-C3N4 nanosheets according to XRD, EDX, SEM and TEM results. A fast electron transport network can be constructed in 3D architecture formed with g-C3N4 nanosheets and CuS nanoparticles, which can afford multi-direction channels for electron transport and accessible catalytic active sites for reduction of polysulfide electrolyte. The synergistic effect of composite CE with continuous conductive network structure shows the excellent catalytic activity and fast electron mobilization. Electrochemical impedance spectrum reveals that the electrochemical property of g-C3N4/CuS composite CE in QDSCs has been changed significantly with the different composition of g-C3N4 and CuS, which is utilized to analyze why QDSC based on CN/30CuS CE shows the best photovoltaic properties of PCE of 5.10%. The new g-C3N4/CuS composite CE with the merits of low cost, easy processing and considerable photovoltaic performance is beneficial to large scale commercial use of three-generation solar cells.