ABSTRACT
The optimization of field-effect mobility in polymer field-effect transistors (FETs) is a critical parameter for advancing organic electronics. Today, many challenges still persist in understanding the roles of the design and processing of semiconducting polymers toward electronic performance. To address this, a facile approach to solution processing using blends of PDPP-TVT and PTPA-3CN is developed, resulting in a 3.5-fold increase in hole mobility and retained stability in electrical performance over 3 cm2 V-1 s-1 after 20 weeks. The amorphous D-A conjugated structure and strong intramolecular polarity of PTPA-3CN are identified as major contributors to the observed improvements in mobility. Additionally, the composite analysis by X-ray photoelectron spectroscopy (XPS) and the flash differential scanning calorimetry (DSC) technique showed a uniform distribution and was well mixed in binary polymer systems. This mobility enhancement technique has also been successfully applied to other polymer semiconductor systems, offering a new design strategy for blending-type organic transistor systems. This blending methodology holds great promise for the practical applications of OFETs.
ABSTRACT
Gels of semiconducting polymers have many potential applications, including biomedical devices and sensors. Here, we report a self-assembled gel system consisting of isoindigo-based semiconducting polymers with galactose side chains in benign, alcohol-based solvents. Because of the carbohydrate side chains, the modified isoindigo polymers are soluble in alcohols. We obtained thermoreversible gels in 1-propanol using these polymers and di-Fmoc-l-lysine, a molecular gelator. The polymers and molecular gelators have been selected in such a way that they do not have significant physical interactions. The molecular gelator self-assembled to form a fibrous structure that confines the polymer chains in the interstitial spaces of the fibers. The polymer chains formed local aggregations and increased the shear moduli of the gels significantly. Bulky galactose side chains and the less planar nature of the polymer backbone hindered the formation of long-range assembled structures of the polymers. However, the dispersion of polymers throughout the gel samples resulted in a percolated structure in the dried gel films. The bulk electrical conductivity of dried gels confirmed the presence of such percolated structures. Our results demonstrated that carbohydrate-containing conjugated polymers can be combined with molecular gelators to obtain gels in eco-friendly solvents.
ABSTRACT
Semiconducting polymers are at the forefront of next-generation organic electronics due to their robust mechanical and optoelectronic properties. However, their extended π-conjugation often leads to materials with low solubilities in common organic solvents, thus requiring processing in high-boiling-point and toxic halogenated solvents to generate thin-film devices. To address this environmental concern, a natural product-inspired side-chain engineering approach was used to incorporate galactose-containing moieties into semiconducting polymers toward improved processability in greener solvents. Novel isoindigo-based polymers with different ratios of galactose-containing side chains were synthesized to improve the solubilities of the organic semiconductors in alcohol-based solvents. The addition of carbohydrate-containing side chains to π-conjugated polymers was found to considerably impact the intermolecular aggregation of the materials and their microstructures in the solid state as confirmed by atomic force microscopy and grazing-incidence wide-angle X-ray scattering. The charge transport characteristics of the new semiconductors were evaluated by the fabrication of organic field-effect transistors prepared from both toxic halogenated and greener alcohol-based solvents. Importantly, the incorporation of carbohydrate-containing side chains was shown to have very little detrimental impact on the electronic properties of the polymer when processed from green solvents.
