Thermal analysis study of antimony chloride and thiourea containing precursors for antimony sulfide thin films

This study investigated the thermal decomposition of precursors for Sb 2 S 3 thin films, obtained by drying methanolic solutions containing SbCl 3 and thiourea (SC(NH 2 ) 2 , tu) at molar ratios of 1:3 ( 1 ) and 1:6 ( 2 ). Simultaneous TG/DTG/DTA/EGA-MS measurements were performed on both 1 and 2 in synthetic air (80% Ar + 20% O 2 ), while 1 was also studied in argon. 1 was identified as the complex compound Sb(tu) 3 Cl 3 , whereas 2 consisted of a mixture of Sb(tu) 3 Cl 3 and uncoordinated thiourea. In argon, the thermal decomposition of 1 occurred between 145 and 660 °C in three steps, with a total mass loss of 91.0%, yielding metallic Sb as the final product. In synthetic air, decomposition of 1 proceeded in three steps between 145 and 620 °C with a total mass loss of 88.0%, while 2 also decomposed in three steps between 150 and 610 °C with a total mass loss of 91.9%. The final product of 1 at 620 °C and 2 at 610 °C in air was Sb 2 O 4 . According to XRD, thermal decomposition of 1 results in crystalline Sb 2 S 3 phase at 230 °C, while using 2 enables deposition of crystalline Sb 2 S 3 at lower temperatures, already at 170 °C. XRD confirms the presence of the Sb 2 S 3 phase up to 400 °C for 1 and 335 °C for 2 . Sb 2 O 3 phase formation for 2 occurs at lower temperature, at around 400 °C, compared to that for 1 at around 460 °C. The main gases evolved during the whole decomposition process were CS 2 and HNCS, that upon oxidation yield COS, SO 2 , CO 2 , HCN, H 2 NCN and NH 3 . Based on the results of thermogravimetric and evolved gas analyses combined with phase composition analysis of solid decomposition products, possible chemical reactions at various steps of decomposition are proposed. This study provides, for the first time, a scientifically grounded basis for optimizing solution composition and processing temperatures for the fabrication of Sb 2 S 3 thin films using wet-chemical methods, such as spray pyrolysis and spin-coating.