Zn‑enriched Cu₂ZnSnS₄ nanocrystals: structure-property optimization for high‑performance energy-relevant photodetectors

Cu2ZnSnS4 (CZTS) nanocrystals have ignited significant scientific and commercial interest due to their favorable optoelectronic properties and earth-abundant constituents. However, synthesizing pure-phase CZTS remains challenging due to its complex phase relationships. In this work, we have synthesized Zn-rich CZTS nanocrystals via hot-injection colloidal method. The tetragonal kesterite phase of CZTS nanocrystals was identified across all Zn concentrations through complementary analyses of X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Energy-dispersive X-ray spectroscopy (EDS) further substantiated near-stoichiometric compositions, with elemental ratios remaining consistent despite systematic variations in Zn. An increase in Zn concentration resulted in a blue shift of the optical band gap, as observed by UV-Visible spectroscopy. Photodetectors fabricated using these Zn-rich CZTS nanocrystals exhibited promising performance, demonstrating a photon responsivity of 8.50 × 10− 6 A/W, a photon detectivity of 19.20 × 105 Jones, a low noise equivalent power of 5.20 × 10− 4 W/Hz1/2, and an external quantum efficiency of 1.92 × 10− 5%. These results highlight the potential of Zn-enriched CZTS nanocrystals for high-performance optoelectronic devices.