2, Georgia Institute of Technology, Atlanta, Georgia, United States
3, Imperial College London, London, , United Kingdom
4, Technion - Israel Institute of Technology, Haifa, , Israel
In recent years, polymeric materials have attracted vast interest in the field of organic electronics, photonics and bioelectronics. One widespread use of π-conjugated polymers has been seen in the area of organic photovoltaics (OPVs). This is because of the promise this interesting class of ‘plastics’ offer for good processability and mechanical flexibility, and their potential to open pathways to print or coat devices onto any surface, including large-area structures. However, due to the low dielectric constant of most polymers (∼2 to ∼4), dissociation of coulombically-bound, photo-generated excitons into fully separated charges is challenging, resulting in high recombination losses and low device efficiencies . We demonstrate here that blending of polymers may allow us to combine desired properties of individual components to enhance exciton generation, charge separation and transport, without the need to introduce all functionalities in a single material. We present a strategy to provide pathways that should assist to manipulate the dielectric constant of OPV blends by introducing poly(vinylene fluoride) (PVDF)  into donor:acceptor blends using solution deposition methods. We show that PVDF affects the phase morphology and other relevant microstructural features of the donor:acceptor system. For this purpose, we use binary (donor polymer:PVDF) and ternary (donor:acceptor:PVDF) phase diagrams constructed from differential scanning calorimetry (DSC) and visualized by vapor phase infiltration (VPI)  and scanning electron microscopy (SEM) techniques. We correlate photo-physical processes and device characteristics with these ternary blend microstructures, and demonstrate that by controlling device phase morphology and its dielectric properties, we gain an additional tool to manipulate device functions.
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