Effects of surface modification of indium tin oxide electrodes on the performance of molecular multilayer organic photovoltaic devices

We investigate the effects of surface modification of indium tin oxide (ITO) on the performance of organic multilayer molecular photovoltaic devices based on pentacene/C-60 bi-layer heterojunctions. Values of the open-circuit voltage (V-oc), short circuit current density (J(sc)), fill factor (FF), and power conversion efficiency (eta) are found invariant of the work function and surface hydrophobicity of ITO. Insensitivity of these parameters to variations of work function in the range of 4.50 to 5.40 eV achieved through the use of surface modifiers are correlated with an invariance of the barrier height (similar to 0.6 eV) due to Fermi level pinning at the ITO/pentacene interface. Energy barrier heights are extracted independently from the analysis of the electrical characteristics of single-layer diodes based on modified ITO and pentacene using an equivalent circuit model.