A-Reum Han

Boosting the Ambipolar Performance of Solution-Processable Polymer Semiconductors via Hybrid Side-Chain Engineering

Ambipolar polymer semiconductors are highly suited for use in flexible, printable, and large-area electronics as they exhibit both n-type (electron-transporting) and p-type (hole-transporting) operations within a single layer. This allows for cost-effective fabrication of complementary circuits with high noise immunity and operational stability. Currently, the performance of ambipolar polymer semiconductors lags behind that of their unipolar counterparts. Here, we report on the side-chain engineering of conjugated, alternating electron donor-acceptor (D-A) polymers using diketopyrrolopyrrole-selenophene copolymers with hybrid siloxane-solubilizing groups (PTDPPSe-Si) to enhance ambipolar performance. The alkyl spacer length of the hybrid side chains was systematically tuned to boost ambipolar performance. The optimized three-dimensional (3-D) charge transport of PTDPPSe-Si with pentyl spacers yielded unprecedentedly high hole and electron mobilities of 8.84 and 4.34 cm(2) V(-1) s(-1), respectively. These results provide guidelines for the molecular design of semiconducting polymers with hybrid side chains.

Solution-Processable Ambipolar Diketopyrrolopyrrole–Selenophene Polymer with Unprecedentedly High Hole and Electron Mobilities

There is a fast-growing demand for polymer-based ambipolar thin-film transistors (TFTs), in which both n-type and p-type transistor operations are realized in a single layer, while maintaining simplicity in processing. Research progress toward this end is essentially fueled by molecular engineering of the conjugated backbones of the polymers and the development of process architectures for device fabrication, which has recently led to hole and electron mobilities of more than 1.0 cm(2) V(-1) s(-1). However, ambipolar polymers with even higher performance are still required. By taking into account both the conjugated backbone and side chains of the polymer component, we have developed a dithienyl-diketopyrrolopyrrole (TDPP) and selenophene containing polymer with hybrid siloxane-solubilizing groups (PTDPPSe-Si). A synergistic combination of rational polymer backbone design, side-chain dynamics, and solution processing affords an enormous boost in ambipolar TFT performance, resulting in unprecedentedly high hole and electron mobilities of 3.97 and 2.20 cm(2) V(-1) s(-1), respectively.

Flexible FET-Type VEGF Aptasensor Based on Nitrogen-Doped Graphene Converted from Conducting Polymer

Graphene-based field-effect transistors (FETs) have been developed rapidly and are currently considered as an alternative for postsilicon electronics. In this study, polypyrrole-converted nitrogen-doped few-layer graphene (PPy-NDFLG) was grown on Cu substrate by chemical vapor deposition combined with vapor deposition polymerization and then transferred onto a flexible substrate. Furthermore, antivascular endothelial growth factor (VEGF) RNA aptamer conjugated PPy-NDFLG was integrated into a liquid-ion gated FET geometry to fabricate a high-performance VEGF aptamer-based sensor. Field-induced high sensitivity was observed for the analyte-binding events, eventually leading to the recognition of the target molecules at an unprecedentedly low concentration (100 fM). Additionally, the aptasensor had excellent reusability, mechanical bendability, and durability in the flexible process. The developed methodology describes, for the first time, the fabrication of N-doped graphene using conducting polymers including heteroatoms in their structures as the carbonization precursor and demonstrates its use in a high-performance, flexible FET-type aptasensor to detect vascular endothelial growth factor as a cancer biomarker.

Highly sensitive and selective liquid-phase sensors based on a solvent-resistant organic-transistor platform.

Liquid-phase sensing of various organic solvents is performed for the first time, using a solvent-resistant organic-transistor platform. Sensors composed of a cross-linked poly(3-hexylthiophene) (P3HT)-azide co-polymer and a calixarene derivative exhibit highly sensitive and selective sensing behavior, owing to the selective binding effects of the liquid analytes with the calixarene-functionalized P3HT-azide, extending the range of their use in practical applications.

High-Performance Furan-Containing Conjugated Polymer for Environmentally Benign Solution Processing

Developing semiconducting polymers that exhibit both strong charge transport capability via highly ordered structures and good processability in environmentally benign solvents remains a challenge. Given that furan-based materials have better solubility in various solvents than analogous thiophene-based materials, we have synthesized and characterized furanyl-diketopyrrolopyrrole polymer (PFDPPTT-Si) together with its thienyl-diketopyrrolopyrrole-based analogue (PTDPPTT-Si) to understand subtle changes induced by the use of furan instead of thiophene units. PTDPPTT-Si films processed in common chlorinated solvent exhibit a higher hole mobility (3.57 cm2 V-1 s-1) than PFDPPTT-Si films (2.40 cm2 V-1 s-1) under the same conditions; this greater hole mobility is a result of tightly aggregated π-stacking structures in PTDPPTT-Si. By contrast, because of its enhanced solubility, PFDPPTT-Si using chlorine-free solution processing results in a device with higher mobility (as high as 1.87 cm2 V-1 s-1) compared to that of the corresponding device fabricated using PTDPPTT-Si. This mobility of 1.87 cm2 V-1 s-1 represents the highest performances among furan-containing polymers reported to the best of our knowledge for nonchlorinated solvents. Our study demonstrates an important step toward environmentally compatible electronics, and we expect the results of our study to reinvigorate the furan-containing semiconductors field.

Siloxane-Based Hybrid Semiconducting Polymers Prepared by Fluoride-Mediated Suzuki Polymerization†

Siloxane-containing materials are a large and important class of organic-inorganic hybrids. In this report, a practical variation of the Suzuki polymerization to generate semiconducting polymeric hybrids based on siloxane units, which proceeds under essentially nonbasic conditions, is presented. This method generates solution-processable poly(diketopyrrolopyrrole-alt-benzothiadiazole) (PDPPBT-Si) consisting of the hybrid siloxane substituents, which could not be made using conventional methods. PDPPBT-Si exhibits excellent ambipolar transistor performance with well-balanced hole and electron FET mobilities. The siloxane-containing DPP-thiophene polymer classes (PDPP3T-Si and PDPP4T-Si), synthesized by this method, exhibit high hole mobility of up to 1.29 cm(2)  V(-1)  s(-1) . This synthetic approach should provide access to a variety of novel siloxane-containing conjugated semiconductor classes by using a variety of aryldihalides and aryldiboronic acids/esters.

Tuning polarity and improving charge transport in organic semiconductors

Although state-of-the-art ambipolar polymer semiconductors have been extensively reported in recent years, highperformance ambipolar polymers with tunable dominant polarity are still required to realize on-demand, target-specific, high-performance organic circuitry. Herein, dithienyl-diketopyrrolopyrrole (TDPP)-based polymer semiconductors with engineered side-chains have been synthesized, characterized and employed in ambipolar organic field-effect transistors, in order to achieve controllable and improved electrical properties. Thermally removable tert-butoxycarbonyl (t-BOC) groups and hybrid siloxane-solubilizing groups are introduced as the solubilizing groups, and they are found to enable the tunable dominant polarity and the enhanced ambipolar performance, respectively. Such outstanding performance based on our molecular design strategies makes these ambipolar polymer semiconductors highly promising for low-cost, large-area, and flexible electronics.