In-situ surface engineering of ternary eco-friendly QDs for enhanced photoelectrochemical hydrogen production

Ternary I-III-VI quantum dots (QDs) have recently received wide attention in solar energy conversion technologies because of their non-toxicity, tunable band gap, and composition-dependant properties. However, their complex non-stoichiometry induces high density of surface traps/defects which significantly affects solar energy conversion efficiencies and long-term stability. This work presents an in-situ growth passivation approach to encapsulate ternary Cu:ZnInSe with ZnSeS alloyed shell (CZISe/ZSeS QDs) as light harvesters for solar-driven photoelectrochemical (PEC) hydrogen (H 2 ) production. The engineered CZISe/ZSeS QDs coupled with TiO 2 -MWCNTs hybrid photoanode exhibit a high photocurrent density of 13.15 mA/cm 2 at 0.8 V vs RHE under 1 sun illumination, which is 20.5 % higher than bare CZISe QDs/TiO 2 photoanode based device. In addition, we observed a 48 % enhancement in the long-term stability with ~88 % current retained after 6000 s. These results indicate that the effective shell passivation has mitigated the surface traps/defects, leading to suppressed charge recombination and improved charge transfer efficiency, as confirmed by optoelectronic, carrier dynamics measurements and theoretical simulations. The findings hold great promise on improving the performance of ternary/multinary eco-friendly colloidal QDs by surface engineering for effective utilization in solar energy conversion technologies. • Surface passivation of Cu:ZnInSe QDs with ZnSeS is a promising approach. • Core/shell QDs offer reduced traps and improved carrier dynamics. • Core/shell QDs-PEC device achieved ~21 % improvement over control QDs. • Optimized PEC system retained ~88 % photocurrent after 6000 s illumination.