Recrystallization of Cu-In-S thin films studied in situ by energy-dispersive X-ray diffraction

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 monitored in situ via diffraction 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 CuInS₂ reflection 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 CuIn₅S₈ phase, 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.