Improving Charge Carrier Mobility of Polymer Blend Field Effect Transistors with Majority Insulating Polymer Phase

The key approach to achieve high performance field effect transistor fabricated from semiconducting/insulating polymer blends with majority insulating polymer phase is the formation of connected fibrous structures of semiconducting polymer and good interfacial interaction of semiconducting polymer with the dielectric layer. Herein, tetrahydrofuran (THF) as a marginal solvent was used as an additive in marginal/good solvent mixtures to control the crystallite structure, phase segregation, and hole transport properties of poly(3-hexylthiophene)/poly(styrene) (P3HT/PS; weight ratio: 1/4) blends, with the advantage that marginal/good solvent mixture gives P3HT sufficient time for phase segregation and relatively better solvent quality to aggregate to more stable structures compared to other reported strategies as bad/good solvent mixtures or directly marginal solvents. Incorporation of THF reduces the P3HT solubility, forming connected fibrous structures as observed in both neat P3HT and blend films; it appears these structures are responsible for improved charge transport. Furthermore, enhanced molecular ordering, π–π stacking and conjugation length are observed with increasing THF amount. THF promotes the edge-on orientation and more stable crystal structures in P3HT, while the lattice spacing remains the same. Finally, the added THF increases hole mobility for P3HT/PS blend FETs, reaching a maximum value of 4 0.0 × 10–³ cm²/(V s) with 20 vol % THF and being comparative to neat P3HT; however, THF has an insignificant influence on the hole mobility for neat P3HT FETs. Morphological characterization supports the idea that differential solubility creates both enhanced chain ordering and vertical phase segregation that both improve FET performance. These results are promising for the development of environmentally stable and lower cost polymer electronics.