Green and room-temperature synthesis of aqueous CuInS2 and Cu2SnS3 nanocrystals for efficient photoelectrochemical water splitting

Abstract

In this work, green synthesis of aqueous ternary CuInS2 (CIS) and Cu2SnS3 (CTS) nanocrystals has been realized by a simple one-pot mixing route. The synthesis is performed at room temperature without using long-chain capping agents, possessing ecofriendly, low-cost and low-energy-consuming merits. The chalcopyrite CIS nanocrystals with a size of 3–5 nm exhibit a prominent photoluminescence peak at 713 nm, revealing a bandgap of 1.74 eV. Sensitization of the nanocrystals on the surface of ZnO nanorod arrays is achieved through spin-coating followed by thermal treatment. Both the CIS and CTS nanocrystals-sensitized ZnO nanorod arrays grown on F-doped tin oxide (FTO) glass substrates are utilized as the photoanodes for efficient photoelectrochemical (PEC) water splitting. After sensitization, the photocurrent density at 1.23 V vs. NHE increases from 0.46 mA cm−2 for the bare ZnO photoanode to 5.98 mA cm−2 for the ZnO/CIS photoanode and 4.85 mA cm−2 for the ZnO/CTS photoanode under one Sun illumination. The significant enhancement in PEC performance is attributed to the expanded optical absorption throughout the visible light region and the stepwise energy band alignment between ZnO and CIS/CTS facilitating for fast charge separation and transport. Our work demonstrates an appealing strategy to synthesize aqueous ternary nanocrystals by green chemistry for efficient solar energy conversion devices.