Heterostructured core/gradient multi-shell quantum dots for high-performance and durable photoelectrochemical hydrogen generation

Colloidal Quantum dots (QDs) are considered promising light harvesters for photoelectrochemical (PEC) hydrogen generation devices due to their size tunable optoelectronic properties. However, the solar-to-hydrogen (STH) efficiency and long-term stability of devices based on QDs are still relatively low, thus limiting the commercial development. These limitations are attributed to the limited absorption range of QDs, unfavorable band energy alignment and photo-oxidation. Here we propose and realize two core/multiple-shell architecture based on CdSe/CdS/ZnS QDs. The shell composition is optimized with gradient layers, forming CdSe/CdSexS1-x/CdS/ZnyCd1-yS/ZnS core/multiple-shell structures, which reduces the surface traps and defects of QDs and simultaneously suppresses exciton recombination by providing intermediated alloyed interlayers. The PEC device based on a mesoporous TiO2 sensitized with two types of core/multiple-shell QDs exhibited an outstanding saturated photocurrent density of 20.5 mA/cm(2) for alloyed core/multiple-shell QDs, under one sun illumination (AM 1.5 G, 100 mW/cm(2)). To our knowledge, this is comparable to the highest value reported so far for the PEC devices based on colloidal QDs. In addition, the as-prepared PEC devices exhibited excellent stability, maintaining similar to 93.4 % of the initial photocurrent density after 2-hour continuous illumination (100 mW/cm(2)). This work provides an efficient approach for improving the performance of PEC devices through QDs structure engineering.