Understanding defect-related issues limiting efficiency of CIGS solar cells

Many electrical characteristics of Cu(In,Ga)Se2-based solar cells, including current–voltage characteristics, are affected by specific properties of negative-U defects in the absorber. We present these characteristics and discuss them in the framework of a VSe–VCu defect model proposed by Lany and Zunger. We show how these defects influence photocarrier transport and the dominant recombination mechanism, and hence also the photovoltaic parameters of the cells. Numerical simulations validating our approach will also be presented.