Simulating Material Inhomogeneities and Defects in CIGS Thin-film Solar Cells

Thin-film CIGS solar cells are simulated using a hybrid model consisting of a distributed form of the analytical one diode model paired with a numerical finite element model of the d.c. conduction in the front contact layers. Variations in material quality over the substrate surface., from measured J-V curves, are incorporated into the model and the effects of cell width and window layer thickness are evaluated for homogeneous and inhomogeneous material quality. Furthermore, the effects of discrete shunt defects of different sizes are modelled, and in different positions on the cell surface. The results from optimizing cell width and window layer thickness show that the effects of material inhomogeneities include a small shift of the optimal parameters together with a less pronounced maximum. As expected, the defect size is important to the shunt conductance parameter of the resulting J-V curves. The passivating effect of the highly resistive ZnO layer is confirmed. Copyright (C) 2009 John Wiley & Sons, Ltd.