Manipulating the Optically Active Defect–Defect Interaction of Colloidal Quantum Dots for Carbon Dioxide Photoreduction

Defect engineering in colloidal quantum dots (QDs), a typical photocatalytic material, is promising to tailor optoelectronic properties and achieve solar-to-fuel energy conversion. However, understanding the effect of defect–defect interactions on both charge carrier and catalytic dynamics is still challenging. Here, we report a class of defect-engineered copper-deficient Zn-doped CuInS2 (ZCIS) QDs that synergistically utilize copper vacancy and Cu2+ defect states to realize CO2 photoreduction. Steady and transient optical characterizations reveal that the density of copper vacancy can manipulate the distribution of optically active Cu+ and Cu2+ defect states (appearing as CuIn″ and CuCu• species, respectively), wherein the Cu+ defect states suppress interband absorption and sharpen the Shockley–Read–Hall recombination, while Cu2+ defect states enable the prolonged exciton lifetime of QDs. In situ infrared spectroscopic investigation and theoretical density functional calculation demonstrate the photoactive Cu2+ defect states nearby the copper vacancy in ZCIS QDs can effectively activate CO2 to the COOH* intermediates, leading to a remarkable photocatalytic CO production rate up to 532.3 μmol g–1 h–1 (turnover number ∼1963) after 120 h illumination.