Phase Equilibria of Cu-In-Se III. The In₂Se₃-Se-Cu₂Se Subsystem

Abstract

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°C, 800°C, and 500°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 a phase (CuInSe 2 ), a semiconductor with promising properties for thin-film solar cells. At 500°C, the typical temperature for the fabrication of such solar cells, the a 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.