Fill factor in organic solar cells

In this paper, we report the dependence of fill factor (FF) on different parameters in organic solar cells. FF is a more sensitive parameter compared to open-circuit voltage (V-OC) and short-circuit current density (J(SC)), and depends on the mobility (mu)-lifetime (tau) product of the bulk material, thickness of the active-polymer layer and on the morphology of the cathode-polymer interface. The curvature of the JV characteristics in the fourth quadrant (which can be adjudged by the sign of d(2)J/dV(2) in the range V-sat50%) to concave (FF<12.5%) depending upon these parameters. A general trend of convex shaped JV characteristics (d(2)J/dV(2)>0) for illuminated devices with good cathode-polymer interfaces and linear or concave JV response (d(2)J/dV(2)<0) for inefficient cathode-polymer interfaces has been observed, where the bulk material properties (the mu tau product) and the thickness of the active layer was favourable for high FF. (C) 2008 Elsevier B.V. All rights reserved.