Microemulsion-controlled synthesis of CoSe₂/CoSeO₃ composite crystals for electrocatalysis in dye-sensitized solar cells

Cobalt diselenide/cobalt selenite (CoSe₂/CoSeO₃) composite crystals with nanocube (NC), nanorod (NR), and nanoparticle (NP) structures were obtained through a microemulsion-assisted hydrothermal synthesis by incorporating the anionic surfactant docusate sodium salt (AOT), the cationic surfactant cetyltrimethyl ammonium bromide (CTAB), and the non-ionic surfactant Triton^® X-100, respectively. The as-prepared CoSe₂/CoSeO₃ crystals were utilized as the electrocatalysts in dye-sensitized solar cells (DSSCs). Among all the crystals, the one obtained through Triton^® X-100 enables its DSSC to achieve the best power conversion efficiency (η) of 9.27%, which is even better than that of the DSSC with platinum (Pt) (7.91%). The catalytic abilities of the counter electrodes were analyzed by cyclic voltammetry (CV), Tafel polarization plots, and electrochemical impedance spectra (EIS). The photovoltaic behaviors are substantiated by incident photon-to-electron conversion efficiency (IPCE) spectra. The DSSC with CoSe₂/CoSeO₃-NP exhibited an η of 9.27% at 100 mW cm⁻², a better η of 9.31% at 50 mW cm⁻², and the best η of 9.41% at 10 mW cm⁻², thereby extending the scope of application of this DSSC from outdoor to indoor regions. The earth abundant, low-cost material of CoSe₂/CoSeO₃-NP can be a promising electrocatalytic material to replace the expensive Pt in a DSSC.