High efficiency photoelectrochemical hydrogen generation using eco-friendly Cu doped Zn-In-Se colloidal quantum dots

Photoelectrochemical (PEC) cells using colloidal quantum dots (QDs) as sensitizers are promising for efficient hydrogen (H₂) production, due to their low cost and to the size/shape/composition dependent optoelectronic properties of QDs. However, QDs that are typically used in PEC cell fabrication contain highly toxic heavy metals (e.g. Pb and Cd) cations, that limit commercial-scale applications. Herein, we synthesized eco-friendly Cu doped Zn-In-Se colloidal QDs and used them in PEC cells to efficiently produce H₂ from water. PEC cells fabricated with optimized Cu (5%) doped Zn-In-Se (Zn:In=1:4) QDs/TiO₂ photoanodes yield an unprecedented saturated photocurrent density of 11.23 mA cm⁻² at 0.8 V vs. RHE under one sun illumination (AM 1.5, 100 mW·cm⁻²) and maintain ~60% of the initial photocurrent density value after 6000 s continuous illumination by using Na₂S/Na₂SO₃ as hole scavenger. This new record value of photocurrent density from eco-friendly QDs based PEC cell demonstrates that an optimized amount of Cu dopant and Zn:In ratio significantly improves light absorption, carrier injection rates/lifetime and the spatial separation of electron-hole pairs. Our work indicates that Cu doped Zn-In-Se QDs can be used as efficient light harvesters to realize high efficiency, inexpensive and environmentally friendly solar-driven production of chemical fuels and other optoelectronic devices.