Temperature-Controlled Phase Separation Behavior of Conjugated Polymer:Elastomer Blends of PffBT4T-2OD and SEBS

Polymer semiconductors are of great interest for the fabrication of high-performance stretchable electronics. Blending these polymers with an elastomer to form nanoconfined nanofibrils has been demonstrated as a promising method to boost or maintain the electronic performance and mechanical compliance of thin films. Preaggregation of the polymer semiconductor in solution may occur in these blends. These solution-state aggregates can strongly impact film morphology and device performance. However, an understanding of the correlation between the solution states’ aggregation and the resulting film morphology is needed to establish qualitative correlations with charge transport. In this work, polymer semiconductor aggregation in solution was experimentally varied by exploiting the temperature-dependent aggregation behavior of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)- alt -(3,3′′′-di(2-octyldodecyl)2,2′;5′,2′′5′′2′′′-quarterthiophen-5,5′′′-diyl)] (PffBT4T-2OD), which was blended with polystyrene- block -poly(ethylene- ran -butylene)- block -polystyrene (SEBS) elastomer. Solution Ultraviolet–Visible Spectroscopy showed a monotonically decreasing amount of PffBT4T-2OD aggregation with increasing temperature in solutions. In contrast, PffBT4T-2OD aggregation and charge carrier mobility in the resulting thin films peaked at an intermediate substrate deposition temperature of 60 °C. The difference in trend between the solution and film state can be attributed to changes that may have occurred during the film drying process. As the deposition temperature increased, the rate of film drying increased, which led to a faster formation of PffBT4T-2OD aggregates. Therefore, the final film aggregation amount depends on both the solution aggregation state and the film formation process. This work suggests that to fabricate high-performance devices, an optimal amount of solution preaggregation and a slower aggregation rate during spin-coating are desirable for creating films with a greater degree of final aggregation compared to films fabricated from solutions with minimal solution preaggregation and faster aggregation rates. The results of this work are relevant to further understanding of conjugated polymer:elastomer blends for stretchable electronics.