Thermal decomposition of thiourea complexes of Cu(I), Zn(II), and Sn(II) chlorides as precursors for the spray pyrolysis deposition of sulfide thin films

Abstract

Comparative study on thermal decomposition of four thiourea–metal complexes, solid precursors for spray pyrolysis deposition (SPD) methods, had been carried out by using thermoanalytical and X-ray diffraction (XRD) methods in combination. [Cu2(tu)6]Cl2·2H2O (1), ZnCl2(tu)2 (2), Sn2Cl4(tu)5·2H2O (3), and SnCl2(tu) (4) prepared from aqueous thiourea (tu) solutions, had been decomposed in a simultaneous thermogravimetric/differential thermoanalytical (TG/DTA) apparatus, while XRD phase analysis of solid residues obtained at various temperatures had been performed. In static air, a main degradation step between 200°C and 300°C led to the formation of Cu9S5 (digenite), ZnS (zinc blende), and SnS2 (berndtite), respectively. Unfortunately, some chemical species with low volatility still remained in condensed phase, while above 400°C, primary oxidation products of sulfides such as Cu2O(SO4) (dolerophanite), ZnO, and SnO2 also occurred. Nevertheless, intermittent spray pyrolysis depositions of Cu2SnS3 and Cu2ZnSnS4 films from some thiourea solutions with Cu(I), Zn(II), and Sn(II) onto glass substrates, with temperature ranging between 225°C and 300°C, were successful.