Transparent Cu2−xSe@N-doped carbon nanosheets as a cathode for Co(III/II)-mediated bifacial dye-sensitized solar cells

Abstract

It is important to develop high-performance and low-cost Pt-free counter electrodes (CEs) for Co2+/Co3+-mediated dye-sensitized solar cells (DSSCs). Herein, transparent Cu2−xSe@N-doped carbon nanosheets were synthesized in situ using a Cu-TCPP metal–organic framework thin film as a template in the presence of selenium powder under nitrogen atmosphere. The Co-mediated bifacial DSSCs fabricated with Cu2−xSe@N-doped carbon nanosheet films as CEs achieved power conversion efficiencies of 7.61% and 5.82% with front and rear irradiation respectively, which is comparable performance to that of DSSCs with Pt CEs (8.46% and 6.23% with front and rear irradiation, respectively). Electrochemical impedance spectroscopy and Tafel measurement results demonstrated the outstanding catalytic ability of the Cu2−xSe@N-doped carbon film to reduce Co3+, which was attributed to the synergistic effects of the homogenous carbon nanosheet structure, the in-situ preparation method, and the uniformly distributed Cu2−xSe nanoparticles. This work shows the tremendous potential of transparent Cu2–xSe@N-doped carbon nanosheets as CEs for industrialization of low-cost Co-mediated bifacial DSSCs.