ИСТИНА

Despite of the great progress for the recent decade, the efficiencies of organic solar cells (OSC) are still significantly lower than those of inorganic ones. Theoretical modeling of the OSC operation can predict their ultimate efficiency and provide a roadmap for their further improvement. In this study, we formulate an OSC model suggesting the kinetic, i.e. non-equilibrium, nature of the OSC operation. We focus on the process of charge separation according to the two-step charge generation model via intermediate hot charge-transfer (CT) states. The first step, CT state formation, is described by Marcus model [1], while the second step, CT state dissociation into free charges, is described by Onsager-Braun theory [2] modified to account for the excess energy (“hotness”) of the states. In our modeling, excess energy is responsible for increased mobility of the non-thermalized charges upon CT state dissociation, which is in accordance with the recent experimental findings [3]. Within the frames of the suggested model, we address the impacts of the optical bandgap, driving force, geminate recombination rate, charge mobility, average electron-hole separation in CT state, dielectric permittivity and reorganization energy on the organic solar cell efficiency. Our results show that the best way to increase the OSC efficiency is to use materials with low reorganization energy. The model also advises to use relatively large bandgaps (ca. 1.5-1.8 eV) as compared to that suggested by the Shockley-Quiesser model. We compare our findings with that of the previously proposed models and discuss the physical reasons underlying the obtained results.