Long-range crystal alignment with polymer additive for organic thin film transistors

In this work, we study for the first time the effect of a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer to control the crystal growth of solution-processed, small-molecule organic semiconductors and to improve the device performance of organic thin film transistors (OTFTs). A benchmark semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was employed to blend with the polymer additive. The TIPS pentacene blend film with 5% PVDF-HFP by weight ratio exhibited a significant morphology enhancement with crystals strictly aligned in long-range order. In particular, it showed an average grain width of 69.98 μm and a misorientation angle of 6.6°, which is a 3.5-fold increase and a 7-fold reduction as compared to the pristine TIPS pentacene film. The bottom-gate, top-contact TIPS pentacene OTFTs with PVDF-HFP polymer additive were fabricated. Electrical characterization showed a hole mobility of up to 0.1 cm²/Vs with 5% PVDF-HFP. The performance improvement of TIPS pentacene/PVDF-HFP based OTFTs can be attributed to the reduced amount of charge trap centers at the enlarged grain width, alleviated crystal misorientation and increased areal coverage. This facile approach to blend PVDF-HFP additive to align crystals and improve orientation in long-range order as demonstrated in this work can be useful for controlling the crystallization and charge transport of other small-molecule organic semiconductors for application in organic electronics on large-scale flexible substrate.