Direct vapour transport grown Cu₂SnS₃ crystals: exploring structural, elastic, optical, and electronic properties

Copper tin sulphide (Cu₂SnS₃) (CTS) has emerged as a potent material for applications in photovoltaic, thermoelectric, electrochemical, biological, and other fields. CTS has superior properties such as non-toxicity, direct bandgap, p-type conductivity, variable crystal structure, alterable morphology and ease of synthesis, and it is a better substitute for conventional semiconductor materials. In the present work, CTS crystals were grown using direct vapour transport. Investigation through X-ray diffraction showed that the as-grown CTS crystals possessed a cubic unit cell structure with a = b = c = 5.403 Å. The analysis of the binding energies and composition of constituents of the as-grown CTS crystals via X-ray photoelectron spectroscopy confirmed the presence of Cu¹⁺, Sn⁴⁺ and S^2-. The experimental bandgap of CTS crystals is 1.23 eV, which was confirmed by diffuse reflectance spectroscopy. The investigation of elastic, optical, thermal and electronic properties of CTS crystals was carried out via density functional theory employing generalized gradient approximation with the Perdew-Burke-Ernzerhof exchange-relationship functional. The first-ever analysis of the temperature-dependent elastic properties of CTS crystals revealed greater stability at elevated temperature (953 K). Dielectric properties, reflectivity, refractive index, loss function, extinction and absorption coefficients of CTS crystals were computed and analyzed in detail. The evaluation of the electronic band structure with density of states revealed valence band maximum and conduction band energy level contributions, showing a bandgap of 1.2 eV. The obtained results are discussed in detail.