Influence of phonon anharmonicity on Raman spectra of Cu2ZnSn(S,Se)4 polycrystalline thin films through computational study

Cu2ZnSn(S,Se)4 (CZT(S,Se)) thin films exhibit the characteristics necessary to be effective absorbers in solar cells. In this report, the room temperature experimental Raman scattering spectra, recorded at different excitation wavelengths, are systematically analyzed theoretically using the results of DFT harmonic frequencies calculations at the Gamma-point for various modifications of kesterite (KS), stannite (ST), and pre-mixed Cu-Au (PMCA) crystal structures. The specific anharmonism-induced features in the spectra of CZT(S,Se) crystals are identified, and the spectral lineshapes at varied strengths of anharmonic interaction are simulated. A robust agreement between the experimental Raman spectrum and the theoretical results is demonstrated, ensuring the reliability of estimating parameters related to anharmonic effects. Therefore, our findings show that incorporating anharmonism as an additional contribution to the phonon spectra, particularly in non-resonant cases, allows for a more accurate description of the vibrational properties of CZT(S,Se). This could play a crucial role in distinguishing between different phases of CZT(S,Se) materials and open new possibilities for the fabrication of solar cells with enhanced characteristics.