Hollow NiSe2 nanospheres grown on graphene with unconventional dual-vacancies in dye-sensitized solar cells

Highlights: • NiSe₂/RGO catalysts were formed at 400 °C (NiSe₂-400) and 450 °C (NiSe₂-450). • The NiSe₂-400 and NiSe₂-450 show Ni-Se and Se-Ni-Se vacancies, respectively. • The dual-vacancies enable NiSe₂-400 superior catalytic performances as CE. Although nickel-based counter electrodes display good catalytic properties in dye-sensitized solar cells (DSSCs), there are challenges to achieve efficient activity for practical device. Except that, vacancy can effectively regulate electrocatalytic efficiency for the catalytic reactions, which take place on the surface of catalysts. Thereby, the hollow Ni_0.85Se nanospheres grown on the reduced graphite oxide (RGO) were designed to attain the composites utilizing a facile hydrothermal strategy, and followed by heating within argon atmosphere at 400 °C (NiSe₂-400) and 450 °C (NiSe₂-450), forming NiSe₂/RGO composite catalysts with abundant vacancies. Importantly, the resultant NiSe₂-400 as counter electrode (CE) exhibits superior electrochemical properties in DSSCs, thus yielding a remarkable photovoltaic performance (8.93%), which may originate from the existence of the appropriate Ni-Se dual vacancies, accelerating the I₃⁻ reduction. The work would provide a strategy for the synthesis of other non-noble metal compounds with unconventional dual vacancies to develop the application of DSSCs.