Solution processability is a key advantage of organic solar cells over the inorganic counterparts. The phase separation between donor and acceptor molecules within the active layer of the device is key to the recombination rate and ultimately the performance of an organic solar cell. It is important to examine conformational changes of these molecules during thin film deposition to better understand this phase separation. Molecular dynamics (MD) simulation is a suitable technique to resolve these molecular scale motions. We utilize MD to simulate systems containing conjugated polymers, fullerenes, and organic solvents and examine properties of these organic blend solutions at different concentrations, emulating progressive stages of solvent evaporation. Two different types of systems were studied using this framework. First, we simulate binary systems of polymer and solvent molecules to fundamentally examine the shapes of conjugated polymer aggregates. Structure and dynamics of these aggregates are quantified and the results are compared to those of known polymer models to develop an understanding of conjugated polymer physics. In addition, we simulate tertiary systems including polymer, fullerene, and solvent molecules to investigate the phase separation process between polymer donors and fullerene acceptors during solvent evaporation. The results from these smaller scale all-atom MD simulations are used to inform larger scale coarse-grained MD simulations to examine experimentally comparable phase separation domain sizes.

Multiscale simulation of solution phase behavior during organic solar cell processing

253rd National Meeting (2017)

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