Device Characteristics of Semiconducting/ Insulating Polymer Blended Organic Field Effect Transistors with Variable Insulating Polymer’s Molecular Weight

The current market trend for electronics is moving past rigid devices and create flexible electronics for uses such as bioelectronics, organic solar cells, organic light emitting diodes, and much more. Although different methods have been employed to create these flexible devices, solution processable semiconducting polymers are promising given their ability to be finely tuned for specific uses and to create large-area, low-cost devices. The mechanical flexibility of state-of-the-art semiconducting polymers is limited by their semi-crystalline nature. Previous work has improved the mechanical properties of these devices by blending a semiconducting and an insulating polymer, which allows for the creation of flexible devices while maintaining or even promoting charge transport. However, an in-depth understanding of the parameters (e.g. processing conditions and polymer structure) required to fine-tune the phase behavior of these blended systems does not yet exist. In addition, the effect of the morphology on charge transport must also be better understood. In this study, the insulating polymer’s molecular weight is varied to understand its’ effect on the overall film morphology. Molecular weight has known influence on the phase separation thermodynamics of two-polymer systems. Spincast films of Diketopyrrolopyrrole (DPP)-based conjugated polymer blended with various molecular weights of polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) in solution were studied. Their morphologies were analyzed by optical (UV-Vis) spectroscopy, grazing incidence wide-angle x-ray scattering (GIWAXS), and atomic force microscopy (AFM) to better understand the aggregation and planarization of the polymer backbone, crystallinity, and phase separation in the films. The charge transport was then studied through the creation of bottom gate/bottom contact and bottom gate/top contact organic field effect transistors (OFETs) due to the vertical phase separation present within the system. This study allows a greater understanding of the requirements for fine-tuning solution processable thin films with good charge transport.