Green” Cu@ZnInSe/ZnSeS Core/Composition Gradient Shell Quantum Dots for Boosted Photoelectrochemical Hydrogen Production

Colloidal quantum dots (QDs) are considered building blocks for solar energy devices due to their promising optoelectronic properties, such as size/shape/composition-dependent absorption and emission spectrum and high absorption coefficient. However, well-performing QDs in solar energy conversion technologies (i.e. photovoltaics or clean fuel production) are typically containing toxic heavy metals (e.g., Cd and Pb), which restricts their commercial applications. In this context, eco-friendly Cu-doped ZnInSe QDs emerged as a promising alternative due to their unique merits, including the long lifetime of charge carriers and suitable band structure for charge injection. Nonetheless, the sensitivity of the plain Cu:ZnInSe QDs may induce surface defects that act as charge recombination centers, leading to a severe deterioration of the photoelectrochemical (PEC) performance. The growth of suitable shell material is a promising approach for effective suppression of surface related defects/traps states and obtain a tailored optical response of QDs.<br/>Here, we report the synthesis of Cu:ZnInSe/ZnSeS core/composition gradient shell with tuneable shell thickness to understand the influence on optoelectronic properties, consequently PEC performance for hydrogen production. An optimized thick composition gradient shell obtained with low Se/S ratio (n = 2 and r =0.05) showed broader absorption toward longer wavelength and high PL quantum yield. Resulting PEC device based on the Cu@ZnInSe/ZnSeS core/shell QDs with n =2 and r = 0.05 exhibited an excellent saturated photocurrent density of 11.7 mA/cm²(at 1 V vs RHE) under one sun illumination (AM 1.5 G, 100 mW/cm²), which is 96% higher than the achieved value of bare Cu@ZnInSe QDs. The investigation and its findings will be presented in detail, exploring how controlled composition gradient shell thickness influences surface passivation and carrier dynamics. In addition, the significance of composition gradient shell layer to achieve enhanced device performance will be discussed, highlighting its great potential for future eco-friendly core/shell QD-based solar energy technologies.