Investigation of substrate temperature effect on physical properties of sprayed Cu 2 MgSnS 4 thin films for solar cells and humidity sensing applications

Cu 2 MgSnS 4 (CMTS) thin films have been grown on glass substrates by spray pyrolysis at different substrate temperatures (Ts = 180, 210, 240, 270 and 300 °C) using ethanol as solvent. The effect of substrate temperature variation on structural, morphological, optical and PL properties has been studied using X-ray diffraction, Scanning Electron, Transmission Electron, High-Resolution Transmission Electron Microscopies and Selected Area Electron Diffraction, Raman and UV–visible spectroscopies, and fluorescence spectroscopy, respectively. The XRD and SAED results revealed that all CMTS films are polycrystalline with kesterite phase taking reticular plane (112) as preferred orientation. A maximum crystallite size of 22 nm value was found at 210 °C substrate temperature. Moreover, surface morphology of CMTS thin films has revealed a smooth, dense and continuous surface at Ts = 210 °C with spherical particles. Optical properties have shown a wide variation in band gap energy in the range of [1.2–1.63] eV with a small change in the absorption coefficient around 4 10 4 cm −1 in the visible range. The optimum value of E g = 1.5 eV was achieved at Ts = 210 °C which offers to CMTS thin films good properties for solar cell applications. PL measurements indicate that CMTS thin films have a strong blue peak emission centered at 404 nm wavelength which can be probably due to the presence of oxygen vacancies and/or impurities. A specific experimental apparatus was prepared to measure the humidity detecting properties of CMTS thin film deposited at Ts = 210 °C for different controlled relative humidity atmosphere (RH) from 22 to 95%. A maximum sensitivity of 95.5% was achieved for RH = 95%. These results show that CMTS thin film grown at Ts = 210 °C can be considered as a performant humidity sensor.