Mechanochemically Synthesized Nanocrystalline Cu2ZnSnSe4 as a Multifunctional Material for Energy Conversion and Storage Applications

Cu2ZnSnSe4 is a promising light-absorbing material for cost-effective and eco-friendly thin-film solar cells; however, its synthesis often leads to secondary phases that limit device efficiency. To overcome these challenges, we devised a straightforward and efficient method to obtain single-phase Cu2ZnSnSe4 nanocrystalline powders directly from the elements Cu, Zn, Sn, and Se via mechanochemical synthesis followed by vacuum annealing at 450 °C. Phase evolution monitored by X-ray diffraction (XRD) and Raman spectroscopy at two-hour milling intervals confirmed the formation of phase-pure kesterite Cu2ZnSnSe4 and enabled tracking of transient secondary phases. Raman spectra revealed the characteristic A1 vibrational modes of the kesterite structure, while XRD peaks and Rietveld refinement (χ2 ~ 1) validated single-phase formation with crystallite sizes of 10–15 nm and dislocation densities of 3.00–3.20 1015 lines/m2. Optical analysis showed a direct bandgap of ~1.1 eV, and estimated linear and nonlinear optical constants validate its potential for photovoltaic applications. Scanning electron microscopy (SEM) analysis showed uniformly distributed particles 50–60 nm, and energy dispersive X-ray (EDS) analysis confirmed a near-stoichiometric Cu:Zn:Sn:Se ratio of 2:1:1:4. X-ray photoelectron spectroscopy (XPS) identified the expected oxidation states (Cu+, Zn2+, Sn4+, and Se2−). Electrical characterization revealed p-type conductivity with a mobility (μ) of 2.09 cm2/Vs, sheet resistance (ρ) of 4.87 Ω cm, and carrier concentrations of 1.23 × 1019 cm−3. Galvanostatic charge–discharge testing (GCD) demonstrated an energy density of 2.872 Wh/kg−1 and a power density of 1083 W kg−1, highlighting the material’s additional potential for energy storage applications.