Recrystallization of Cu–In–S thin films studiedin situby energy-dispersive X-ray diffraction

Abstract

The recrystallization of Cu–In–S thin films has been monitored in real time by means of synchrotron-based energy-dispersive X-ray diffraction. To trigger recrystallization, nanocrystalline Cu–In–S layers with [Cu]/[In] < 1 were covered with layers of CuS or pure Cu, so that the overall ratio [Cu]/[In] > 1. The bilayer films were heated to 773 K and the evolution of the microstructure was monitoredin situ viadiffraction spectra. In the first step of the analysis, the diffraction data were used to identify solid-state phase transitions as a function of temperature. In a further step, single-line profile analysis of the 112 CuInS2reflection was used to study grain growth in this material system. The recrystallization was investigated under two sulfur pressure conditions and for different [Cu]/[In] ratios. The recrystallization is composed of three steps: consumption of the CuIn5S8phase, grain growth, and a transition from the Cu–Au-type to the chalcopyrite-type structure of CuInS2. Increasing the sulfur pressure during heating systematically reduces the temperature at which grain growth sets in. Various paths to control the recrystallization of Cu–In–S thin films are proposed.