Understand the importance of molecular organization at polymer–polymer interfaces in excitonic solar cells

Abstract

To improve the photovoltaic power conversion efficiency of organic solar cells it is necessary to increase the open circuit voltage and short circuit current. Prior work has shown that both these device properties can be improved by using donor–acceptor systems composed of two polymers, which favors excitons dissociation and charge generation, and subsequent charge transport to the electrodes. However, device performance depends strongly on the experimental conditions under which the device was created, because they determine the molecular structure of the interface between the two polymers. Polymer chains can have different conformations relative to the interface, creating different arrangements of the conjugated segments whose disorder degree can affect energy and charge transfer. Thus, understanding this effect is of utmost importance to improve the efficiency of all-polymer excitonic solar cells. In this work, we present the results obtained using a Monte Carlo model that takes into account the arrangement of the polymer strands at polymer–polymer interfaces and considers the main physical processes mediating exciton and charge dynamics. Our results show that the amount of charge extracted from the interface is sensitive to the orientation of polymer strands at interfaces and on the diffusive layer width formed by the mixture of both polymers.