Investigation of substrate temperature effect on physical properties of sprayed Cu2MgSnS4 thin films for solar cells and humidity sensing applications

Cu2MgSnS4 (CMTS) thin films have been grown on glass substrates by spray pyrolysis at different substrate temperatures (Ts = 180, 210, 240, 270 and 300 degrees 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 degrees C substrate temperature. Moreover, surface morphology of CMTS thin films has revealed a smooth, dense and continuous surface at Ts = 210 degrees 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 degrees 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 degrees 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 degrees C can be considered as a performant humidity sensor.

Automated summary

In this study, Cu2MgSnS4 (CMTS) thin films were successfully grown on glass substrates by spray pyrolysis, and the effect of substrate temperature on their structural, morphological, optical and PL properties was investigated. The results showed that CMTS films grown at a substrate temperature of 210 degrees C exhibited the optimal crystallite size, smooth surface, and suitable band gap energy for solar cell applications. Additionally, the CMTS films demonstrated high sensitivity as a humidity sensor.