Nature-Inspired Semiconducting Polymers with Peptide Conjugation Breakers for Intrinsically Stretchable and Self-Healable Transistors

Intrinsically stretchable and self-healable polymer semiconductors have recently been extensively studied for flexible and wearable electronics. However, challenges lie in the scarcity of molecular designs, laborious synthesis, and an incomplete understanding of energy dissipation mechanisms. Nature-inspired peptide conjugation breakers (PCBs) can provide a robust system for expanding the molecular scope systematically due to the structural diversity of peptides concerning steric bulkiness and polarity. In this study, novel intrinsically stretchable and self-healable semiconducting polymers are developed by integrating PCBs into a diketopyrrolopyrrole moiety, and the distinct roles of intermolecular and intramolecular hydrogen bonds in stretchability are investigated. The former mainly disrupts chain packing and results in reduced crystallinity, while the latter restricts the conformational flexibility of the chain. Remarkably, the polymer containing a glycine-based PCB demonstrates a high mobility of 0.12 cm2 V–1 s–1 with good cyclic durability and a crack-onset strain exceeding 100%. Mobility remains stable even at 100% strain in both rigid and fully stretchable transistors with self-healing characteristics. These results, for the first time, underscore the usefulness of nature-inspired moieties in stretchable and self-healable electronics and provide a molecular design strategy that balances intermolecular and intramolecular hydrogen bonds, thereby yielding desirable electrical and mechanical properties

Naphthalene Diimide Incorporated Thiophene-Free Copolymers with Acene and Heteroacene Units: Comparison of Geometric Features and Electron-Donating Strength of Co-units

A family of naphthalene diimide (NDI)-based donor (D)-acceptor (A) copolymers with various acene- (benzene (Bz), naphthalene (Np), and pyrene (Py)) and heteroacene-type (selenophene (Se) and thiophene (Th)) donor rings has been designed and synthesized as a means to systematically understand structure–property relationships on the subject of the structural factor and electron-donating capability of the donor portions for applications in organic field-effect transistors (OFETs) based on NDIs. Alongside of two categories dealing with the lack or existence of the heteroatoms in the donor framework, the resulting copolymers can also be classified into ‘thiophene-free’ D–A copolymers (<b>PNDI-Bz</b>, <b>PNDI-Np</b>, <b>PNDI-Py</b>, and <b>PNDI-Se</b>) and thiophene-containing copolymer (<b>PNDI-Th</b>). The results from optical and electronic properties lead to the determination that the empirical electron-donating strength of donor co-units is in the order of Bz < Np < Py < Th < Se. In contrast with the similarity of the LUMO levels (−3.73∼−3.82 eV) due to the dominant NDI contribution to the polymer backbone, the HOMO levels are sensitive to the relative electron-donating ability and shown to primarily influence whether unipolar <i>n</i>-channel (<b>PNDI-Bz</b> and <b>PNDI-Np</b>) or ambipolar charge transport (<b>PNDI-Py</b>, <b>PNDI-Se</b>, and <b>PNDI-Th</b>) is observed in OFETs of the NDI-based copolymers. Intriguingly, regardless of the strong electron donors toward efficient intramolecular charge transfer (ICT), the best OFET performance is observed in the acene-based centrosymmetric copolymer <b>PNDI-Np</b> (5.63 × 10^–2 cm² V^–1 s^–1) when compared to those of the other copolymers with axisymmetric units. Thus, the present work highlights that the geometric features of the donors in NDI D–A copolymers strongly reflect the carrier mobility dynamics rather than inserting electron-rich donor moieties into the backbone to lower the band gap and further strengthen ICT

β‑Alkyl substituted Dithieno[2,3‑<i>d</i>;2′,3′<i>-d</i>′]benzo[1,2‑<i>b</i>;4,5‑<i>b</i>′]dithiophene Semiconducting Materials and Their Application to Solution-Processed Organic Transistors

A novel highly π-extended heteroacene with four symmetrically fused thiophene-ring units and solubilizing substituents at the terminal β-positions on the central ring, dithieno­[2,3-<i>d</i>;2′,3′<i>-d</i>′]­benzo­[1,2-<i>b</i>;4,5-<i>b</i>′]­dithiophene (DTBDT) was synthesized via intramolecular electrophilic coupling reaction. The α-positions availability in the DTBDT motif enables the preparation of solution-processable DTBDT-based polymers such as <b>PDTBDT</b>, <b>PDTBDT-BT</b>, <b>PDTBDT-DTBT</b>, and <b>PDTBDT-DTDPP</b>. Even with its highly extended acene-like π-framework, all polymers show fairly good environmental stability of their highest occupied molecular orbitals (HOMOs) from −5.21 to −5.59 eV. In the course of our study to assess a profile of semiconductor properties, field-effect transistor performance of the four DTBDT-containing copolymers via solution-process is characterized, and <b>PDTBDT-DTDPP</b> exhibits the best electrical performance with a hole mobility of 1.70 × 10^–2 cm² V^–1 s^–1. <b>PDTBDT-DTDPP</b> has a relatively smaller charge injection barrier for a hole from the gold electrodes and maintains good coplanarity of the polymer backbone, indicating the enhanced π–π stacking characteristic and charge carrier transport. The experimental results demonstrate that our molecular design strategy for air-stable, high-performance organic semiconductors is highly promising

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 <i>n</i>-type and <i>p</i>-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 cm² 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 (<b>PTDPPSe-Si</b>). 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 cm² V^–1 s^–1, respectively

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 <i>n</i>-type (electron-transporting) and <i>p</i>-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 (<b>PTDPPSe-Si</b>) 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 <b>PTDPPSe-Si</b> with pentyl spacers yielded unprecedentedly high hole and electron mobilities of 8.84 and 4.34 cm² V^–1 s^–1, respectively. These results provide guidelines for the molecular design of semiconducting polymers with hybrid side chains

Requirements for Forming Efficient 3‑D Charge Transport Pathway in Diketopyrrolopyrrole-Based Copolymers: Film Morphology vs Molecular Packing

To achieve extremely high planarity and processability simultaneously, we have newly designed and synthesized copolymers composed of donor units of 2,2′-(2,5-dialkoxy-1,4-phenylene)­dithieno­[3,2-<i>b</i>]­thiophene (TT-P-TT) and acceptor units of diketopyrrolopyrrole (DPP). These copolymers consist of a highly planar backbone due to intramolecular interactions. We have systematically investigated the effects of intermolecular interactions by controlling the side chain bulkiness on the polymer thin-film morphologies, packing structures, and charge transport. The thin-film microstructures of the copolymers are found to be critically dependent upon subtle changes in the intermolecular interactions, and charge transport dynamics of the copolymer based field-effect transistors (FETs) has been investigated by in-depth structure–property relationship study. Although the size of the fibrillar structures increases as the bulkiness of the side chains in the copolymer increases, the copolymer with the smallest side chain shows remarkably high charge carrier mobility. Our findings reveal the requirement for forming efficient 3-D charge transport pathway and highlight the importance of the molecular packing and interdomain connectivity, rather than the crystalline domain size. The results obtained herein demonstrate the importance of tailoring the side chain bulkiness and provide new insights into the molecular design for high-performance polymer semiconductors

Fluorinated Benzothiadiazole (BT) Groups as a Powerful Unit for High-Performance Electron-Transporting Polymers

Over the past few years, one of the most remarkable advances in the field of polymer solar cells (PSCs) has been the development of fluorinated 2,1,3-benzothiadiazole (BT)-based polymers that lack the solid working principles of previous designs, but boost the power conversion efficiency. To assess a rich data set for the influence of the fluorinated BT units on the charge-transport characteristics in organic field-effect transistors (OFETs), we synthesized two new polymers (<b>PDPP-FBT</b> and <b>PDPP-2FBT</b>) incorporating diketopyrrolopyrrole (DPP) and either single- or double-fluorinated BT and thoroughly investigated them via a range of techniques. Unlike the small differences in the absorption properties of <b>PDPP-FBT</b> and its nonfluorinated analogue (<b>PDPP-BT</b>), the introduction of doubly fluorinated BT into the polymer backbone induces a noticeable change in its optical profiles and energy levels, which results in a slightly wider bandgap and deeper HOMO for <b>PDPP-2FBT</b>, relative to the others. Grazing incidence X-ray diffraction (GIXD) analysis reveals that both fluorinated polymer films have long-range orders along the out-of-plane direction, and π–π stacking in the in-plane direction, implying semicrystalline lamellar structures with edge-on orientations in the solid state. Thanks to the strong intermolecular interactions and highly electron-deficient π-systems driven by the inclusion of F atoms, the polymers exhibit electron mobilities of up to 0.42 and 0.30 cm² V^–1 s^–1 for <b>PDPP-FBT</b> and <b>PDPP-2FBT</b>, respectively, while maintaining hole mobilities higher than 0.1 cm² V^–1 s^–1. Our results highlight that the use of fluorinated BT blocks in the polymers is a promising molecular design strategy for improving electron transporting performance without sacrificing their original hole mobility values

Determining Optimal Crystallinity of Diketopyrrolopyrrole-Based Terpolymers for Highly Efficient Polymer Solar Cells and Transistors

A new series of conjugated random terpolymers (PDPP2T-Se-Th) was synthesized from an electron-deficient diketopyrrolopyrrole (DPP)-based unit in conjugation with two electron-rich selenophene (Se) and thiophene (Th) species, with a view to inducing different crystalline behaviors of the polymers. The crystallinity of the polymers can be systematically controlled by tuning the ratio between Se and Th; an increase in Se content induced a remarkable increase in the melting and crystallization temperatures as well as the crystallinity of the PDPP2T-Se-Th terpolymers. These changes in the crystalline properties of polymers had a dramatic effect on the performances of organic field-effect transistors (OFETs) and polymer solar cells (PSCs). However, their effect on each type of devices was very different. The charge carrier mobilities of the PDPP2T-Se-Th terpolymers in OFET devices increased remarkably as the Se content increased in the polymers, showing that PDPP2T-Se100 with Se/Th ratio = 100/0 had very high hole and electron mobilities (4.72 and 5.54 cm² V^–1 s^–1, respectively) with well-balanced ambipolar property. In contrast, the best power conversion efficiency (PCE) of 7.2% was observed for the PDPP2T-Se10-Th90 polymers that had Se/Th ratio of 10/90 due to the synergistic contributions from high charge mobility and optimized bulk-heterojunction (BHJ) morphology with fullerene acceptors. To understand the effects of the crystallinity of random terpolymers on their performances in OTFTs and PSCs, we systematically investigated the effects of the Se/Th compositions on their optical, electrical, and structural properties

Polarity and Air-Stability Transitions in Field-Effect Transistors Based on Fullerenes with Different Solubilizing Groups

A series of <i>o</i>-xylene and indene fullerene derivatives with varying frontier molecular orbital energy levels were utilized for assessing the impact of the number of solubilizing groups on the electrical performance of fullerene-based organic-field-effect transistors (OFETs). The charge-carrier polarity was found to be strongly dependent upon the energy levels of fullerene derivatives. The <i>o</i>-xylene C₆₀ monoadduct (OXCMA) and indene C₆₀ monoadduct (ICMA) exhibited unipolar <i>n</i>-channel behaviors with high electron mobilities, whereas the bis- and trisadducts of indene and <i>o</i>-xylene C₆₀ derivatives showed ambipolar charge transport. The OXCMA OFETs fabricated by solution shearing and molecular <i>n</i>-type doping showed an electron mobility of up to 2.28 cm² V^–1 s^–1, which is one of the highest electron mobilities obtained from solution-processed fullerene thin-film devices. Our findings systematically demonstrate the relationship between the energy level and charge-carrier polarity and provide insight into molecular design and processing strategies toward high-performance fullerene-based OFETs

Ambipolar Semiconducting Polymers with <i>π-</i>Spacer Linked Bis-Benzothiadiazole Blocks as Strong Accepting Units

Recognizing the importance of molecular coplanarity and with the aim of developing new, ideal strong acceptor-building units in semiconducting polymers for high-performance organic electronics, herein we present a simplified single-step synthesis of novel vinylene- and acetylene-linked bis-benzothiadiazole (<b>VBBT</b> and <b>ABBT</b>) monomers with enlarged planarity relative to a conventionally used acceptor, benzothiadiazole (BT). Along these lines, four polymers (<b>PDPP-VBBT</b>, <b>PDPP-ABBT</b>, <b>PIID-VBBT</b>, and <b>PIID-ABBT</b>) incorporating either <b>VBBT</b> or <b>ABBT</b> moieties are synthesized by copolymerizing with centro-symmetric ketopyrrole cores, such as diketopyrrolopyrrole (DPP) and isoindigo (IID), and their electronic, physical, and transistor properties are studied. These polymers show relatively balanced ambipolar transport, and <b>PDPP-VBBT</b> yields hole and electron mobilities as high as 0.32 and 0.13 cm² V^–1 s^–1, respectively. Interestingly, the acetylenic linkages lead to enhanced electron transportation in ketopyrrole-based polymers, showing a decreased threshold voltage and inverting voltage in the transistor and inverter devices, respectively. The IID-based BBT polymers exhibit the inversion of the dominant polarity depending on the type of unsaturated carbon bridge. Owing to their strong electron-accepting ability and their highly π-extended and planar structures, <b>VBBT</b> and <b>ABBT</b> monomers should be extended to the rational design of high-performance polymers in the field of organic electronics