Modification of surface and interface of copper indium gallium selenide thin films with sulfurization

In this work, sulfur distribution in the surface and bulk of copper indium gallium selenide (CIGS) thin films and CIGS/molybdenum (Mo) interface after sulfurization was investigated. The morphology of the surfaces and cross-sections of the thin films was observed by scanning electron microscopy. X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to study the phases, structures and chemical components of the thin films. After sulfurization, the grain size became larger and a sulfur-contained phase could be found in the XRD pattern. Interestingly, Raman spectroscopy and XPS indicated that sulfur was abundant not only in the surface but also in the CIGS/molybdenum interface. Besides, the chemical state of indium in the surface was also modified by the annealing treatment. These results help in understanding the complicated interface behavior of CIGS solar cells and benefit the improvement of the devices.