Optimized optical band gap energy and Urbach tail of Cr2S3 thin films by Sn incorporation for optoelectronic applications

In this study, the Cr2S3-based thin films were successfully prepared by a simple chemical spray pyrolysis method. The effect of Sn2+ incorporation at different contents (0 <= Sn2+ <= 0.25 mol) on the microstructural, optical, and optoelectrical properties of the thin films was investigated. The formation of high purity Cr2S3 and Sn-doped Cr2S3 thin films with a rhombohedral crystalline phase was confirmed by the grazing incident X-ray diffraction results and energy dispersive X-ray analysis. The surface morphology of thin films was observed using field emission scanning electron microscopy. The optical band gap energy and width of the Urbach tail were evaluated as a function of Sn2+ doping from the optical absorption coefficient of the samples. By increasing the Sn2+ content, a considerable narrowing of about 0.50 eV was observed in the optical band gap energy; while the Urbach energy was found to gradually increase up to 0.992 eV for the sample containing a high-content of Sn2+. A linear relationship between the optical band gap and Urbach energies was also proposed. Finally, the effect of optically changes on the photosensing performance and time-response switching of the pure Cr2S3 and Sn-doped Cr2S3 thin films was studied for the first time, in which the photosensitivity of the samples enhanced over 25 times, as the content of Sn2+ increased into the Cr2S3 host structure.