Utilizing morphological correlators for device performance to optimize ternary blend organic solar cells based on block copolymer additives

Abstract

In a recent work, we studied donor-acceptor blend based organic photovoltaics and, by utilizing a combination of morphology simulations and device modeling, demonstrated that block copolymer compatibilizers with appropriately selected energy levels can be used in such systems to give rise to highly efficient devices that, in some cases, can even outperform idealized morphologies. In the present study, we probe whether morphological simulations can be used in conjunction with simple morphological descriptors as a means to screen the performance characteristics of such energy cascade based ternary blend devices as predicted using device-level simulations. Towards this objective, we present results from different parameter combinations to demonstrate that the domain size, percolation ratio, tortuosity of domains, and concentration gradient at the interface between donors and acceptors correlate strongly with the device performance of such ternary blend systems. Subsequently, we present extensive parameter studies where we simultaneously vary the blend composition, the degree of polymerization of the donor homopolymer, and the acceptor composition of the donor-b-acceptor block copolymer to identify blend formulations that give rise to such optimal morphological and device characteristics. Finally, we demonstrate that, while the overall device performance depends on a combination of morphological factors, the morphological descriptors identified in our work may help identify promising blend formulations.