Optical Properties of Cu(In,Ga)Se2

Abstract

In Cu(In,Ga)Se2 (CIGSe) solar cells, a precise control of the CIGSe elemental composition is crucial to achieve high conversion efficiencies. In particular, for CIGSe layers incorporated into solar cells, compositionally graded structures are formed intentionally to suppress the carrier recombination at the front and rear interfaces. In designing complex CIGSe solar cells, the determination and understanding of fundamental CIGSe optical properties are of significant importance. In this chapter, high-precision characterization of CIGSe dielectric functions based on multi-sample spectroscopic ellipsometry analyses is presented. Moreover, this chapter focuses on the variations of the optical properties with the Cu and Ga compositions. From the systematic critical point analyses performed for the extracted dielectric functions, the optical transitions in CIGSe are discussed. This chapter further explains a complete CIGSe optical database, from which the optical constants of CIGSe for arbitrary Cu and Ga compositions can be determined.