Development and application of novel multiscale modeling techniques for studying the loss processes in polymer solar cell nanodevices

During the past decade significant attention has been focused on study of organic solar cells, representing a promising technology for renewable environmental-friendly energy. In comparison to the inorganic counterparts, the organic photovoltaic devices posses a number of important advantages, however, their application is limited due to low power conversion efficiency up to date. Previous experimental research in the field revealed that the main cause of the low device efficiency was the existence of different loss phenomena, e.g. exciton losses, charge losses, and photon losses. In present thesis, by developing and applying the suitable multiscale modeling techniques, we investigated the role of these losses on the device performance theoretically. Our simulation approach consisted of subsequent application of polymer field theory, for calculating the polymer phase-separated morphology , and dynamical Monte Carlo method for simulating the elementary photovotaic processes. With this methodology in hand, we studied the role of structural inhomogeneities, such as inclusions and dead ends on the device performance, which we found to be crucial for the internal quantum efficiency of the photovoltaic system. Furthermore, we focused on the role of donor- and acceptor-polymer mixing, which we studied by switching from mesoscopic to atomistic scale of the system description. To this end, we showed the the main part of photogenerated charges comes from the region away from the visual domain boundaries in agreement with recent experimental data. Finally, we proposed a novel approach to improve the photovoltaic performance of polymer-bulk heterojunction devices, based on random tapering of a polymer segment encompassing the chemical junctions between the electron-donating and electron-accepting blocks of the diblock copolymer molecules. We demonstrated that by introducing the tapered middle block into the diblock copolymer structure, the increase in internal quantum efficiency can reach 40 %