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

Abstract

To improve the efficiency of organic solar cells is necessary, for instance, to increase the open-circuit voltage or increase sun-light absorption by covering complementary regions of the solar spectrum. This can be achieved by using a donor-acceptor system composed of two polymers. The versatility of these materials has the advantage of enabling the control of morphology at nanoscale, and thus the design of an adequate interface to improve the device efficiency, using for instance nanoimprint lithography. However, proper control of the molecular organization of both polymers at polymer-polymer interface is difficult and strongly depends on the experimental conditions used. Polymer chains can present different conformations relative to the interface, creating different conjugated strand arrangements whose disorder degree can affect energy and charge transfer. Thus, understanding this effect is of utmost importance to improve the efficiency of excitonic solar cells. In this work we present a Monte Carlo model that uses a proper description of polymer-polymer interface nanomorpholy and considers the main physical processes that mediate excitons and charges dynamics. Our results show that the amount of charge extracted from the interface is sensible to polymer strand orientation and to the presence of the diffusive layer formed by the mixture of both polymers.