Achieving 10% Efficiency in Quantum Dot-Sensitized Solar Cells via Vacancy-Engineered Carbon Nitride in CuS/C Heterostructures.

The development of high-efficiency counter electrodes (CEs) is a pivotal challenge for advancing the performance of quantum dot-sensitized solar cells (QDSSCs). This study reports the rational synthesis of a CuS/C-DCNox heterostructure, featuring copper sulfide nanoparticles (CuS) anchored onto a nitrogen-vacancy-rich, mildly oxidized defective carbon nitride matrix (DCNox). The controlled introduction of nitrogen vacancies into the graphitic carbon nitride (g-C3N4) lattice creates mid-gap donor states that enhance n-type conductivity and provide coordinatively unsaturated sites for accelerated polysulfide reduction. The exceptional photovoltaic performance is primarily attributed to these engineered nitrogen vacancies, which modulate the electronic environment, thereby facilitating superior charge dynamics. Mechanistically, the integration of these materials establishes a Mott-Schottky (M-S) p-n junction, driven by the specific alignment of their Fermi levels. This architecture generates a robust built-in electric field (BIEF) at the interface, which significantly promotes spatial charge separation and reduces charge-transfer resistance between the CE and the electrolyte. Consequently, the optimized CuS/C-DCNox CE achieves a champion power conversion efficiency (PCE) of 10.09%, supported by a high JSC of 27.5 mA cm-2, a VOC of 696 mV, and FF of 52.7%. These results demonstrate that nitrogen vacancy engineering is a powerful strategy for regulating interfacial electronic states.