Abstract
In this article, the impact of surface recombination on the J-V characteristics of organic solar cells (OSC) was analyzed. The investigation was carried out using the drift-diffusion model in which the surface recombination of holes and electrons on both electrodes, anode and cathode, were taken into account through boundary conditions. In order to perceive the individual influence of the surface recombination, the equilibrium thermionic concentrations for holes and electrons on contact interfaces were neglected. As the reference point of our analysis, the measured In 2 O 5 Sn/ poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)/poly(3-hexylthiophene-2,5-diyl): indene-C 60 bisadduct /Al solar cell J-V curve was reproduced by our model. The surface recombination velocities (SRVs) for electrons and holes on both contacts were further varied and J-V curves were generated. For simplicity, it was assumed that diffusion current dominates at contacts. For the sake of systematization, three categories of SRV values were introduced, S-small for blocking contact, L-large for conductive contact, and M-medium for contact which is neither blocking nor conductive. The analysis was conducted for different ratios of electron and hole mobilities. It was established that in order to obtain regular J-shape J-V characteristics in OSCs, both contacts should be conductive, for both holes and electrons. This implies that the concept of contact selectivity in OSCs should be reexamined in terms of its physical description and relation to the SRVs values.