Multifunctional Structure-Modified Quaternary Compounds Co9Se8–CuSe2–WSe2 Mixed with MWCNT as a Counter Electrode Material for Dye-Sensitized Solar Cells

In this study, a trimetallic selenide material with a hollow spherical structure (Co9Se8–CuSe2–WSe2) was synthesized through two consecutive solvothermal reactions. The synergistic effect between the quaternary elements, the benefits of the selenization of metals, and the unique morphology led to the prominent electrocatalytic ability of Co9Se8–CuSe2–WSe2 hollow spheres. Co9Se8–CuSe2–WSe2 hollow spheres were then mixed with oxygen plasma-treated multiwalled carbon nanotubes (MWCNT) as counter electrode (CE) material for dye-sensitized solar cells (DSSCs), achieving a photoelectric conversion efficiency (η) of 9.23% under one sun condition (AM 1.5G, 100 mW cm–2), surpassing the 8.08% of devices with platinum counter electrodes (PtCEs). For indoor conditions, a T5 light source was applied to the DSSCs with Co9Se8–CuSe2–WSe2 + MWCNT CE, and the efficiency increased to 14.14% under 3600 lx irradiance. Finally, Co9Se8–CuSe2–WSe2 + MWCNT CE demonstrated good stability with 92.23% retention after 1000 cycles of cyclic voltammetry, exceeding the 82.49% of PtCE. Therefore, Co9Se8–CuSe2–WSe2 + MWCNT shows potential as a substitute for platinum as CE material for DSSCs.