Influence from front contact sheet resistance on extracted diode parameters in CIGS solar cells

The extraction of one-diode model parameters from a current-voltage (J- V) curve is problematic, since the model is one-dimensional while real devices are indeed three-dimensional. Theparameters obtained by fitting the model curve to experimental data depend on how the current is collected, and more specifically the geometry of the contact. This is due to the non-uniform lateral current flow in the window layers, which leads to differentparts of the device experiencing different front contact voltage drop, and hence different operating points on the ideal J- V curve. In this work, finite element simulations of three-dimensional contact structures are performed and compared to experimental data on Cu(In, Ga)Se-2-based solar cell devices. It is concluded that the lateral current flow can influence the extracted parameters from the one-diode model significantly if the resistivity of the front contact material is high, or if there is no current collecting grid structure. These types of situations may appear in damp heat-treated cells and module type cells, respectively. Copyright (c) 2007 John Wiley & Sons, Ltd.