Synthesis and Interface Engineering in Heterojunctions of Tin-Selenide-Based Nanostructures for Photoelectrochemical Water Splitting

SnSe nanomaterials are challenging to use in sustainable energy production due to difficulties in phase-pure synthesis and efficient charge-carrier separation. We demonstrate a systematic facile synthesis method with an in-depth nucleation and growth mechanism for the rational design of phase-pure and morphology-controlled SnSe-based efficient and cost-effective photocatalysts. Transient absorption spectroscopy measurements are performed to investigate the charge-carrier kinetics of SnSe microflowers (MFs), which exhibit a free charge-carrier lifetime of 6.2 ps. Although the bare SnSe, CdSe, and ZnSe photoanodes demonstrate sizable photocurrents, the construction of CdSe/SnSe and ZnSe/SnSe heterojunctions dramatically improves the photoelectrochemical devices activity. The CdSe/SnSe photoanode shows higher photocurrents of 35 μA cm–2, compared to the ZnSe/SnSe (15 μA cm–2) heterojunction and the individual SnSe (10 μA cm–2), CdSe (7 μA cm–2), and ZnSe (1 μA cm–2). The decent photoactivity of the CdSe/SnSe photoanode is attributed to the desired type-II band alignment and very small band offset (0.08 eV) that exists across the interface, which promotes the efficient separation of photogenerated electron–hole pairs confirmed by cyclic voltammetry measurements and is corroborated by first-principles density functional theory calculations. These findings should open new avenues for the design and development of advanced next-generation tin selenide-based heterostructures for efficient PEC water-splitting applications.