Phase equilibria of Cu-In-SeIII.: The In2Se3-Se-Cu2Se subsystem

In three subsequent publications we report new results on the phase equilibria of Cu-In-Se. In part I and part II, we have described the In(2)Se(3)-Cu(2)Se isopleth (subsystem I), which constitutes a quasibinary section, and the InIn(2)Se(3)-Cu(2)Se-Cu subsystem (subsystem II). The present and final part, part III, deals with the subsystem In(2)Se(3)Se-Cu(2)Se (subsystem III) and completes our investigation of the entire composition triangle. For the In(2)Se(3)-Se-Cu(2)Se subsystem we describe the liquidus surface, two reaction schemes of the phase equilibria, and three different isopleths. Isothermal sections at 900 degrees C, 800 degrees C, and 500 degrees C connect this subsystem to the subsystems I and II. Finally, we discuss the phase equilibria of the Cu-In-Se system as a whole. In total, we have found forty four-phase planes in this system, eighteen critical tie lines, and twenty-nine different liquidus surfaces. Monotectic and metatectic critical tie lines establish four surfaces of primary crystallization for the alpha phase (CuInSe(2)), a semiconductor with promising properties for thin-film solar cells. At 500 degrees C, the typical temperature for the fabrication of such solar cells, the alpha phase is in equilibrium with eight solid phases and one liquid phase. Our results help to develop new processing strategies and reveal what kind of complications may occur.