Alloyed shell engineered heavy-metal-free quantum dots for efficient photoelectrochemical hydrogen generation

Heavy-metal-free quantum dots (QDs) based photoelectrochemical (PEC) water splitting has emerged as a promising approach for green hydrogen (H 2 ) production. However, a high density of surface defects/traps substantially limits efficient carrier dynamics and, consequently, overall device performance. In this work, we engineered Cu-Zn-In-Se (Cu-ZISe) QD surfaces by optimizing the alloyed ZnSeS (ZSeS) shell via aluminum (Al) doping to enhance optoelectronic properties and PEC H 2 production performance. The strategic growth of an alloyed ZSeS shell layer effectively passivates surface trap/defect states, promoting a favorable band alignment for efficient carrier dynamics. The incorporation of Al into the alloyed shell layer modulates the electronic band structure and induces the formation of a thin Al-oxide layer, thereby enhancing carrier separation, improving interfacial stability, and enhancing the efficiency of PEC devices. The optimized Cu-ZISe/ZSeS:Al core/alloyed shell QDs-based PEC with polysulfide electrolyte of 0.25 M Na 2 S and 0.35 M Na 2 SO 4 (pH = 14) exhibits a high photocurrent density of 13.91 mA/cm 2 at 1 V under one-sun illumination (AM 1.5G, 100 mW.cm −2 ), which is 65% superior compared to the core Cu-ZISe QDs-based PEC device (8.40 mA/cm 2 at 1 V). Importantly, the PEC device retained 87% and 36% of its initial performance after 2 h and 10 h continuous operation, respectively, under one-sun illumination. This work provides critical insights into alloyed-shell and dopant-assisted engineering strategies for advancing heavy-metal-free QDs-PEC systems toward practical green H 2 production and other QDs-based optoelectronic devices. • Al-ZnSeS alloyed shell passivates core QD surface traps and enhances stability. • Alloyed-shell Al-ZnSeS engineering improves interface quality and carrier dynamics. • PEC device with alloyed-shell QDs yield 65% higher performance than the control QDs. • Stable PEC device with 87% photocurrent retained after 7000 s continuous operation.