Cu 2 ZnSnS 4 and Cu 2 ZnSn(S 1−x Se x ) 4 nanocrystals: room-temperature synthesis and efficient photoelectrochemical water splitting

Green synthesis of Cu 2 ZnSnS 4 (CZTS) and Cu 2 ZnSn(S 1−x Se x ) 4 (CZTSSe) nanocrystals is highly desirable for low-cost and high-efficiency solar energy conversion devices. In this work, scalable synthesis of multinary CZTS and CZTSSe nanocrystals at room temperature has been achieved by a simple metal complex solution mixing (Metcomix) process. In the Metcomix process, CZTS or CZTSSe nanocrystals are formed by simply mixing aqueous solutions of copper thiourea complex ([Cu(TU) 4 ] 2+ ), zinc ammonium complex ([Zn(NH 3 ) 4 ] 2+ ) and tin chalcogen complex ([Sn 2 S 6 ] 4− ) or tin double chalcogen complex ([Sn 2 S 4 Se 2 ] 4− ) at room temperature. The Metcomix process features low-energy-consuming, low-cost, environmentally friendly, high-purity, and scalable-production. The CZTS and CZTSSe nanocrystals have a small size of 4–10 nm and exhibit remarkable room-temperature photoluminescence and optical absorption properties. The CZTS and CZTSSe nanocrystals are also deposited onto ZnO nanorod arrays and demonstrated as efficient photoanodes for photoelectrochemical water splitting. The ZnO/CZTSSe photoanode exhibits a photocurrent density of 9.06 mA cm −2 at 1.23 V ( vs. the NHE) and an optimal applied bias photon-to-current efficiency (ABPE) of ∼3.43% at a bias of 0.60 V. The present work demonstrates a new approach for synthesizing eco-friendly multinary chalcogenide nanocrystals at room temperature and their promising applications in solar energy conversion devices.