Effect of temperature on thermal expansion and anharmonicity in Cu2ZnSnS4 thin films grown by co-sputtering and sulfurization

• CZTS thin film was grown by co-sputtering Cu, Zn and Sn metal targets and sulfurizing it in H2S.
• Temperature-dependent Raman spectroscopic study in the range 80–450 K was carried out.
• Decrease in peak intensity, shift of peak towards lower frequency and increase in the line width is observed.
• These effects are due to thermal expansion, and interaction of the phonon.

Copper zinc tin sulfide (CZTS, made from the earth abundant and non-toxic materials) is a quaternary semiconducting compound which has received increasing interest for solar cells applications. In this study, CZTS thin film has been grown by co-sputtering Cu, Zn and Sn metal targets and sulfurizing it in H2S. XRD, SEM, EDS, XRF and optical studies show that these films are suitable for solar cell applications. The temperature-dependent Raman spectroscopic study on CZTS thin film was carried out in the temperature range of 80–450 K. A decrease in the intensity of “A” mode Raman peaks, shift of Raman peaks towards lower frequency and increase in the line width have been observed with increase in temperature. Raman “A” mode shifts from 337 cm−1 at 80 K to 329 cm−1 at 450 K. The peak at 288 cm−1 disappears when the measurement was taken at 450 K. Based on experimental results and fittings of anharmonic equation; it has been shown that these effects are due to thermal expansion and interaction of the phonon with other phonons which arise at higher temperature. These phonons interact resulting in damping of the “A” mode phonon intensity. It was concluded that in order to truly analyze multicomponent compounds, Raman studies should be carried out at low temperature.