Morphology-controlled Cu₂SnS₃ quantum dot-sensitized solar PEC cells for efficient hydrogen production

Regular shape and size regularity of quantum dots (QDs) significantly influence the photoelectrical properties of solar photoelectrochemical (PEC) cells. Two types of green Cu₂SnS₃ (CTS) QDs, sphere-like and bullet-like, were synthesized via the hot injection method by modulating the ratio of sulfur precursors. Compared with bullet-like CTS QDs, sphere-like CTS QDs exhibit a more negative conduction-band minimum and a narrower bandgap, enhancing sunlight absorption and utilization efficiency. These QDs were deposited onto TiO₂ nanorod arrays individually to form p–n heterojunction photoanodes, which were assembled into PEC cells with Pt-plate counter electrodes for water-splitting H₂ production. The experimental results demonstrate that the sphere-like CTS/TiO₂ photoanode exhibits excellent PEC performance due to its more systematical spherical structure and homogeneous size distribution, achieving a photocurrent density of 2.54 mA cm⁻², a hydrogen production yield of 162.1 μmol cm⁻² within 4-hour illumination (AM 1.5G, 100 mW cm⁻²), and, especially, long-term high stability of hydrogen production for 16 consecutive hours. The enhanced performance of the sphere-like CTS/TiO₂ photoanode is attributed to its superior photoabsorption, shorter charge-carrier diffusion length and improved charge-separation efficiency. By modulating the morphology and size uniformity of CTS QDs as photosensitizers, this work demonstrates a viable strategy to boost the charge separation kinetics and light-harvesting capacity of PEC systems, thereby achieving efficient solar-to-hydrogen conversion.