Thermomechanical and Electrical Properties of Doped, Donor/Acceptor Type Ultra-Thin Polymer Films Organic Electronics Applications

Molecular doping of conjugated polymer materials effectively enhances electrical properties; however, the influence of doping on the thermomechanical properties of ultra-thin films (sub-80 nm), mimicking device conditions, is not well understood. Doping donor/acceptor (D-A) type polymers, such as poly-diketopyrrolopyrrole (DPP), poses challenges due to mismatched energetics of the polymer and dopant. In this study, we introduce side chain engineering of the DPP-type polymer to promote doping . We fabricated ultra-thin films using spin coating followed by mixed/sequential doping for the investigation of doping efficiency, electrical conductivity, mechanical properties, polymer morphology, and crystallinity of modified DPP-type polymers using the following techniques: UV-vis spectroscopy, two-point probe conductivity, pseudo-free-standing film on water mechanical testing, atomic force microscopy, grazing incidence wide-angle X-ray scattering, X-ray photoelectron spectroscopy, thermogravimetric analysis, and flash differential scanning calorimetry. Our results show that engineering DPP-based polymers with electron-donating side chain units, such as polyethylene glycol, enhances doping energetics and imparts unique mechanical properties depending on doping efficiency as well as glass transition temperature of doped thin films. This work establishes a foundation for better understanding and improved doping efficiency of doped D-A type polymeric ultra-thin films for advanced polymer electronics applications.