Thermoanalytical study of precursors for tin sulfide thin films deposited by chemical spray pyrolysis

Abstract

Thermal decomposition of precursors for SnS thin films obtained by drying aqueous solutions of SnCl2 and SC(NH2)2 in the Sn:S molar ratios of 1:1 (1) and 1:8 (2) was monitored by simultaneous thermogravimetry/differential thermal analysis (TG/DTA) measurements in the dynamic 80 % Ar + 20 % O2 atmosphere. The evolved gaseous species from 1 were recorded by simultaneous thermogravimetry/differential thermal analysis/evolved gas analysis–mass spectrometry (TG/DTA/EGA-MS) measurements. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the dried precursors and products of the thermal decomposition. The precursor 1 is a complex compound, Sn(tu)Cl2, while 2 consists of Sn2(tu)5Cl4·H2O and noncomplexed thiourea. The thermal degradation of 1 and 2 in the temperature range of 30–700 °C consists of four steps with a total mass loss of 68.0 and 84.5 %, respectively. According to XRD, the solid decomposition products at 210 °C of 1 are SnS2, (NH4)2SnCl6 and C(NH2)3SnCl3, and of 2 are SnS2, SnS, NH4Cl and (NH4)2SnCl6. Decomposition of 1 and 2 is completed by 550 and 570 °C, respectively. The final decomposition product of 1 and 2 at 700 °C is SnO2. This study shows that the excess of thiourea in the spray solution, compared to that required for the formation of the intermediate tin complex compounds, suppresses the formation of tin oxide phase and depresses the loss of tin species from the system.