Associate Professor, Institute of Applied Physics, University of Tsukuba, Japan.

Speech Title: Relation of thin-film growth on defect generation in Cu(In,Ga)Se₂
Abstract: Characterization of defects in Cu(In,Ga)Se₂ (CIGS)-based solar cells is an important research subject for understanding its carrier recombination processes. In this decade, the optical and electrical response of the defect states have been intensely studied using various analytical methods. Nevertheless, the origin and distribution of the defects in CIGS have not been fully understood yet due to its complex device structures and multinary compositions. During the growth of CIGS, in particular, segregation of the secondary phase, selenization, and alkali metal diffusion occur, and the difficulty in the control of the growth process mainly results in fluctuation of their optoelectronic properties. Therefore, a systematic study on the relation between the thin film growth and the generation of defects is necessary. In this study, we have investigated the impact of growth condition (Se flux and Ga concentration) on defect generation in CIGS by using various characterization techniques. We want to point out that the defect level centered around 0.8 eV from the valence level may act as a recombination center at room temperature. We will discuss whether this defect level acts as a recombination center.
Keywords: CIGS solar cells, defect