N, S Co-doped carbon-encapsulated CoS(Co9S8) hybrid counter electrodes for dye-sensitized solar cells

Unique wool-ball shaped nanocrystalline CoS was synthesized using solvothermal method in which dopamine (DA) was added as carbon source to combine with the CoS. The DA in situ polymerized and coated on the CoS particle surfaces during the solvothermal process. N, S co-doped carbon-encapsulated CoS(Co9S8) were achieved after a post carbonization. In the composites, CoS(Co9S8) nanocrystals and carbon are tightly bound and embedded into the amorphous carbon layer to form a spherical core–shell structure. Hybrid counter electrodes (CEs) fabricated with the product have good conductivity, dispersion and stability due to the synergetic effect between carbon and nanocrystalline CoS(Co9S8). Charge transfer through the CE/electrolyte interfaces is improved by dopamine-carbon combination. In the optimal case, PCE of 8.82% of the dye-sensitized solar cells (DSSCs) with the hybrid CEs was achieved, which is close to that of the cell with Pt (8.86%) CE, and is a 41.12% increase compared with that of CoS CE cell with the structure of photoanode/N719/electrolyte (I−/I3−)/CE. Moreover, stability of the cells with the composite CEs was greatly improved. The results demonstrate that the as-prepared composites are promising alternatives to Pt-CEs for high-performance DSSCs. The reported preparation method will guide further developments in highly efficient carbon-based catalysts for electrochemistry and energy related applications.