Constructing type-II CuInSe₂/CuInS₂ core/shell quantum dots for high-performance photoelectrochemical cells

CuInSe₂ (CISe) quantum dots (QDs) have shown promising applications in photoelectrochemical (PEC) cells due to their nontoxicity, high extinction coefficient, and wide optical absorption range; however, their low PEC performance prevents their applications due to insufficient charge carrier separation and severe charge recombination. Herein, CISe/CuInS₂ (CISe/CIS) core/shell structured QDs are designed and constructed to promote charge separation and diminish interface defects. Afterward, the copper vacancy (V_Cu) state of CISe/CIS QDs is enriched by modulating the precursor molar ratios of In/Cu. Therefore, the radiative recombination of the conduction band edge electrons with the V_Cu localized holes becomes dominant and prolongs the carrier lifetime compared with intrinsic band-to-band recombination, thus promoting charge separation. Consequently, the V_Cu-rich CISe/CIS QD-based photoanode shows a high photocurrent density of 8.0 mA cm⁻², which is one of the highest values reported for CISe QD-based PEC cells. This work provides an effective approach for promoting charge carrier separation and transfer through surface or intrinsic defect mediation for PEC applications of I–III–VI semiconductor nanocrystals.