Thermal behaviour of precursors for CuInS2 thin films deposited by spray pyrolysis

Abstract

The thermal decomposition of precursors for copper indium disulphide (CuInS2) thin films obtained by drying aqueous solutions of copper chloride (CuCl2), indium chloride (InCl3) and thiourea (SC(NH2)2) at the Cu:In:S molar ratios of 1:1:3 (1) and 1:1:6 (2) was monitored by simultaneous thermogravimetry /differential thermal analysis/ evolved gas analysis-mass spectrometry (TG/DTA/EGA-MS) measurements in a dynamic 80 %Ar + 20 %O2 atmosphere. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to characterise the dried precursors and products of the thermal decomposition. The precursors 1 and 2 are mixtures of copper and indium chloride thiourea complex compounds, whilst 1 can also contain unreacted InCl3. The thermal degradation of 1 and 2 in the temperature range of 30–800 °C consists of six steps with a total mass loss of 71.5 and 89.8 %, respectively. According to XRD, CuInS2 is formed below 300 °C. Decomposition of 1 and 2 is completed at 620 and 600 °C, respectively. The final decomposition product of 1 at 800 °C consists of a mixture of In2O3 and CuO phases, whilst 2 consists of In2O3, CuO and Cu2In2O5 phases. EGA by MS revealed the release of CS2, NH3, H2NCN and HNCS, which upon their oxidation also yield COS, SO2, HCN and CO2.