LAUSR

Cu(In,Ga)Se2 (CIGS) solar cells have reached 22.6% efficiency, one of the highest in thin-film solar cells. High-performance CIGS absorber layers are produced by a three-stage co-evaporation technique: first In-Ga-Se is co-evaporated, second Cu-Se is co-evaporated until the [Cu]/([In]+[Ga]) ratio becomes >1, third In-Ga-Se is again co-evaporated until the [Cu]/([In]+[Ga]) ratio becomes <1. Typically, such three-stage processes involve an increase in the temperature from about 300–350°C in the first stage up to about 450–600°C in the second and third stages. It was reported that the Cu excess in the second stage is essential for recrystallization [1]. However, little has been known about how the atomic structures evolve during the recrystallization in the second stage.