Different ligand exchange solvents effect on the densification of CuIn_0.7Ga_0.3Se₂ prepared using the heating-up method

Highlights: • Ligand exchange effect on densification of CuIn_0.7Ga_0.3Se₂ film was studied. • CuIn_0.7Ga_0.3Se₂ was decomposed at temperatures ≥250 °C in air atmosphere. • Residual carbon was reduced after ligand exchange with 1-hexanethiol and m-xylene. • A dense CuIn_0.7Ga_0.3Se₂ film was obtained by ligand-exchanging and sintering. - Abstract: The effects of different ligand exchange solvents and heat treatment conditions on the densification and microstructure development of CuIn_0.7Ga_0.3Se₂ (CIGS) crystallites synthesized using the heating-up method were studied in this work. The heat treatment effects on the organic molecules and crystalline structure were investigated using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was observed that oleylamine (OLA) adsorbed onto the CIGS surface was difficult to remove during sintering. Ligand-exchange with m-xylene or 1-hexanethiol can promote the removal of oleylamine adsorbed onto the CIGS surface and prevent the residual carbon from forming during sintering, which leads to grain growth and densification. A dense CuIn_0.7Ga_0.3Se₂ can be obtained using the precursor powders after ligand-exchange with 1-hexanethiol and m-xylene to remove organic molecules and sintering at 600 °C for 2 h under Se atmosphere.