Efficient and stable heterostructured Co9S8/Cu7S4 composite counter electrodes derived from Prussian blue analogs for quantum dot-sensitized solar cells

The challenge of boosting the efficiency of QDSSCs lies in the rational development and design of economical, stable and efficient counter electrode (CE) catalysts for fast and efficient electron transport at the CE/electrolyte interface. Here, we creatively construct Co ₉S ₈/Cu ₇S ₄ heterostructure composite CEs using CuCo-Prussian blue analogs (PBA) as precursor by one-step in-situ solvothermal vulcanization method. Work function analysis and systematic electrochemical characterizations reveal that the presence of heterojunctions in the Co ₉S ₈/Cu ₇S ₄ can increase the interfacial electric field driving force inside the material, thereby reducing the R _ct at CE/electrolyte interface, promoting the efficient transfer of electrons. Correspondingly, the Co ₉S ₈/Cu ₇S ₄ composite CE can improve the stability and compensate for the deficiency of the single component CE through a decent synergistic catalytic effect. Remarkably, the Mn-CdS/CdSe/ZnS co-sensitized QDSSC equipped with Co ₉S ₈/Cu ₇S ₄ heterostructure composite CE delivers an optimal conversion efficiency of 8.43% with J _sc = 23.42 mA/cm ², V _oc = 0.672 V; FF = 0.54, which was significantly superior to physically mixed CE (PM-Co ₉S ₈/Cu ₇S ₄, 6.55%), single-component CE (Cu ₇S ₄, 5.60%; Co ₉S ₈, 5.13%) and conventional Brass/Cu ₂ S CE (4.96%). In briefly, the advanced heterostructure engineering and the abundant, tunable chemical elemental composition of PBA provide new views for the purposeful design of economical and outstanding heterostructured composite CEs.