(34e) Aggregation Structure and Solvation of  Solution-Phase PTB7

Organic photovoltaics are a low-cost, flexible alternative to traditional silicon-based photovoltaics. The complex kinetically trapped structure of the active layer in organic photovoltaics plays a determining role in the device efficiency. Arguably, the inability to rationally control the mesoscale morphology of the active layer is the limiting step in the successful proliferation of organic photovoltaics. A rigorous understanding of solvation properties of donor and acceptor materials is essential in order to control device morphology. Empirical quantities such as the Hansen solubility parameters have been proposed as a means to quantify solubility, however they have not been widely applied to organic electronics. In this work, we use atomistic molecular simulation coupled with free energy sampling techniques to quantify and understand solubility and structure in organic photovoltaics. We calculate free energies of dissociation for PTB7 oligomers in several widely-used solvents. We compare the resulting solubilities to both experiment and Hansen solubility parameters which we determine in simulation. We suggest that in-silico Hansen solubility parameters can be used for high-throughput screening of solvents in organic electronics due to their close agreement with free energy surfaces of solvation. We also examine the complex array of structures assumed by conjugated organic photovoltaic polymers in a variety of solvents and examine their scaling behaviors.