Overlap concentration generates optimum device performance for DPP-based conjugated polymers

Manipulating the solution phase of conjugated polymers via control of the respective processing parameters results in opportunities to create new morphologies and function. Although the complex processing space of conjugated polymers has been widely investigated, the effect of polymer solution concentration has not been adequately linked to macroscale device performance. This work investigates the influence of the processing parameter, solution concentration, on the OFET performance of donor-acceptor polymers, with a focus on diketopyrrolopyrrole (DPP)-based polymers using solution viscosity experiments. Experiments performed on three different molecular weights (Mw) of poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno- [3,2-b]-thiophene)] (DPP-DTT) revealed that films fabricated at the critical overlap concentration (C*), identified from solution-state viscosity experiments, consistently resulted in improved organic field effect transistor hole mobility. The overlap of polymer chains at C* in the solution state is shown to be related to formation of ordered morphologies that may explain the improved charge transport in the solid film. Furthermore, similar experiments revealed that the trend is observed across other types of DPP-based polymers as well.