Cu-Based Chalcogenide Nanocrystals Cu₂ZnA(SₓSe₄₋ₓ) (A = Al, Ga, In): Synthesis, Characterization, and S–Se Alloying Effects*

We report a new class of Cu-based chalcogenide nanocrystals, Cu₂ZnAS_xSe_4-x, (A= Al, Ga, In), synthesized via a novel modified hot-injection route. Analysis of XRD peak intensities showed that all compositions crystallize into pure wurtzite phase (space group: P6₃mc, no. 186). Scherrer analysis of the peak broadening in the diffraction pattern showed nanocrystal sizes ranging from 3 to 11 nm, consistent with TEM imaging. The materials exhibit a direct band gap with strong absorption in the visible range with estimated bandgaps between 2.2 and 3.0 eV. S-Se alloying allows for fine tuning of bandgaps, with higher Se content correlating with larger crystallite size and lower bandgap. Theoretical calculations using DFT within the virtual crystal approximation also support these observations. PL characterization showed a broad fluorescence spectrum with a peak around 435 nm (2.85 eV). This energy is close to the estimated direct bandgap value, suggesting emission from direct inter-band transitions. Time-Resolved Photoluminescence (TRPL) showed similar lifetimes for all the samples, 2.0-2.5 ns, when fitted with a single exponential decay model. This similarity suggests a common trapping mechanism that dominated the recombination processes in all the samples, most likely hole trapping. In summary, these new materials exhibit tunable optoelectronic properties, making them promising candidates for photovoltaics and light-harvesting applications requiring absorption in the visible range.