Electronic polarizability, single oscillator analysis and optoelectronic properties of Cu2CdSnS4 nanomaterial photoabsorber layer fabricated by spray pyrolysis

The Cu₂CdSnS₄ (CCTS) nanomaterial photoabsorber layers were successfully deposited by spray pyrolysis at substrate temperatures between 300 and 400 °C to investigate the effect of deposition temperature on structural, optical, electronic polarizability, single oscillator characteristics, and optoelectronic features of CCTS thin films. X-ray diffraction analysis showed a phase transformation from cernyite to stannite structure due to temperature changes, accompanied by improved crystallinity. The crystallite size grew from 33.8 to 51.2 nm, while the dislocation density and microstrain dropped from 8.74 × 10¹⁴ to 3.81 × 10¹⁴ m⁻² and from 10.50 × 10⁻³ to 6.91 × 10⁻³, respectively. AFM analysis indicated a slight decrease in surface roughness from 61.4 to 56.8 nm at 350 °C, followed by a sharp increase to 99.95 nm at 400 °C due to grain coarsening. Optical studies showed strong absorption coefficients around 10⁵ cm⁻¹ and a red-shift in the optical band gap from 1.390 to 1.286 eV as the temperature increased. The refractive index increased from 3.06 to 3.14, and the dielectric constant rose from 9.36 to 9.86. Additionally, electronic polarizability and optical susceptibility increased from 2.92 × 10⁻²⁵ to 2.97 × 10⁻²⁵ cm³ and from 0.667 to 0.705, respectively, indicating a better dielectric response and polarization behaviour. Wemple–DiDomenico single oscillator analysis revealed that the dispersion energy increased from 0.63 to 4.96 eV, while the oscillator energy decreased from 5.27 to 1.74 eV, confirming stronger interband optical transitions at higher temperatures. The optoelectronic properties improved remarkable, with the carrier concentration increasing from 3.06 × 10 16 –10.10 × 10 16 cm⁻³, optical mobility improved from 6.89 to 9.89 cm²V⁻¹s⁻¹ while optical resistivity varied from 1.33 × 10² to 3.56 × 10² Ωcm. In summary, 400 °C was identified as suitable deposition temperature for good-performance CCTS solar absorber layers