Intrinsically Stretchable Polymer Semiconductors with Good Ductility and High Charge Mobility through Reducing the Central Symmetry of the Conjugated Backbone Units

Partially Degradable N-Type Conjugated Random Copolymers for Intrinsically Stretchable Organic Field-Effect Transistors

In this study, a series of conjugated homopolymers (P1 and P5) and random copolymers (P2-P4) by copolymerizing naphthalene diimide (NDI) as the acceptor with varying ratios of two donor units, thiophene-imine-thiophene (TIT) and thiophene-vinylene-thiophene (TVT) is developed. The inclusion of TIT imparted degradability to the random copolymers under acidic conditions, offering a sustainable solution for electronic waste management. Structural analysis revealed that TIT favored edge-on molecular orientation, while TVT promoted face-on and end-to-end orientations. The synergistic combination of TIT and TVT in copolymerization resulted in balanced structural and functional properties with partial degradability conferred using the TIT units. The random copolymer P3, with an optimal equimolar TIT/TVT ratio, demonstrates superior electrical and mechanical performance. P3 exhibits an initial charge mobility of 0.10 cm2 V⁻¹ s⁻¹ and maintained mobility of 0.0017 cm2 V⁻¹ s⁻¹ under 20% strain, significantly outperforming P1 in mobility at almost strain levels. P3 also achieved a mobility retention of 31.3% under 20% strain, compared to 12.2% for P5. This study demonstrates that the copolymerization of TIT and TVT enables the fine-tuning of solid-state packing modes and molecular orientations, thereby improving both the stretchability and environmental sustainability of the materials.

Pechmann Dye-Containing Diketopyrrolopyrrole-Based Stretchable Polymer Semiconductors

Conjugated polymer design via random terpolymerization with irregular backbones has emerged as a strategy for stretchable organic electronics, requiring diverse molecular architectures to balance charge carrier mobility (μ) and stretchability. In this study, diketopyrrolopyrrole (DPP)-based conjugated polymers with 0%, 5%, and 10% Pechmann dye (PDy) units, denoted as DP-T0, DP-T5, and DP-T10, respectively, are introduced, and explore the impact of PDy on structural mobility and stretchability through experimental and computational analyses. Electrical measurements reveal hole mobilities ranging from 0.01 to 0.08 cm2 V⁻¹ s⁻¹, with a slight decrease as PDy content increases. Stretchability tests indicate significant improvements in DP-T5 and DP-T10 due to their loosely packed lamellar structures. Notably, DP-T5 achieves a crack onset strain (εc) of 250% and a polarization dichroic ratio (PDR) of 2.4 under 200% strain, leading to a mobility ratio (μ200/μ0) exceeding 5. These results demonstrate that PDy incorporation enhances the mechanical stretchability of DPP-based conjugated polymers while maintaining reasonable electronic performance. This work highlights the potential of PDy-based random terpolymerization for developing stretchable polymer semiconductors.

Conjugated Multiblock Copolymers and Microcracked Gold Electrodes Applied for the Intrinsically Stretchable Field-Effect Transistor

The rise of flexible electronic devices has led to extensive research into conjugated polymer structural engineering. Integrating polymer channels and contact electrodes, warranting high stretchability, is still critical, and the microcracked gold technique provides a potential strategy to integrate them. Conjugated block copolymers have gained significant attention due to their high flexibility, allowing for tailored polymer structures to meet the specific requirements of different device characteristics. In this study, novel N-type multiblock copolymers (multi-BCPs) composed of rigid poly(naphthalene diimide-alt-bithiophene) and flexible polyisobutylene segments were successfully synthesized as polymer semiconductors for the first time. The materials are named based on the weight fraction of soft segments: NDI (0 wt %), mAB73 (27 wt %), and mAB60 (40 wt %). The study explores the mechanical properties, crystallinity, and electrical performance of flexible multi-BCPs. The results show that introducing soft segments significantly enhances stretchability, with crack-onset strains beyond 100% because of their low elastic moduli of 40-50 MPa. Furthermore, the OFET device of mAB73 achieves unchanged mobility under 100% strain, outperforming mAB60 due to excessive polyisobutylene blocks. At the end of this study, an integrated stretchable device with high stretchability is fulfilled by utilizing the microcracked gold technique to combine the multi-BCP channels and contact electrodes. The integrated device can be applied to biomedical electronics without toxic or corrosive electrode materials. The influencing factors, including contact resistance, channel charge mobility, and electrode resistance, are systematically studied to investigate the integrated device's mobility-stretchability relationship. The results indicate that the contact resistance between the multi-BCP channels and contact electrodes is essential to the device's performance. Among these, mAB73, containing soft segments, exhibits more stability than NDI due to the microcracked gold electrodes with infiltrated gold nanoparticles in the rubbery channel surface. Appropriately incorporating soft segments significantly enhances mobility retention under tensile strains, highlighting the potential of multi-BCP designs in stretchable electronic applications.

Recent developments in polymer semiconductors with excellent electron transport performances

Benefiting from molecular design and device innovation, electronic devices based on polymer semiconductors have achieved significant developments and gradual commercialization over the past few decades. Most of high-performance polymer semiconductors that have been prepared exhibit p-type performances, and records of their carrier mobilities are constantly being broken through. Although ambipolar and n-type polymers are necessary for constructing p-n heterojunctions and logic circuits, only a few materials show outstanding device performances, which leads to their developments lagging far behind that of p-type analogues. As a consequence, it is extremely significant to summarize polymer semiconductors with excellent electron transport performances. This review focuses on the design considerations and bonding modes between monomers of polymer semiconductors with high electron mobilities. To enhance electron transport performances of polymer semiconductors, the structural modification strategies are described in detail. Subsequently, the electron transport, thermoelectric, mixed ionic-electronic conduction, intrinsically stretchable, photodetection, and spin transport performances of high-electron mobility polymers are discussed from the perspective of molecular engineering. In the end, the challenges and prospects in this research field are presented, which provide valuable guidance for the design of polymer semiconductors with excellent electron transport performances and the exploration of more advanced applications in the future.

The Multifaceted Role of 3D Printed Conducting Polymers in Next-Generation Energy Devices: A Critical Perspective

The increasing human population is leading to growing consumption of energy sources which requires development in energy devices. The modern iterations of these devices fail to offer sustainable and environmentally friendly answers since they require costly equipment and produce a lot of waste. Three-dimensional (3D) printing has spurred incredible innovation over the years in a variety of fields and is clearly an attractive option because technology can create unique geometric items quickly, cheaply, and with little waste. Conducting polymers (CPs) are a significant family of functional materials that have garnered interest in the research community because of their high conductivity, outstanding sustainability, and economic significance. They have an extensive number of applications involving supercapacitors, power sources, electrochromic gadgets, electrostatic components, conducting pastes, sensors, and biological devices thanks to their special physical and electrical attributes, ease of synthesis, and appropriate frameworks for functional attachment. The use of three-dimensional printing has become popular as an exact way to enhance prepared networks. Rapid technological advancements are reproducing patterns and building structures that enable automated deposition of polymers for intricate structures. Different composites have been created using oxides of metals and carbon to improve the efficiency of the CPs. Such composites have been actively investigated as exceptional energy producers for low-power electronic techniques, and by increasing the range of applications, they have verified increasing surface area, electronic conductivity, and remarkable electrochemical behavior. The hybridization with such materials has produced a range of equipment, such as gathering energy, sensors, protective gadgets, and storage facilities. A few possible uses for these CPs such as sensors and energy storage devices are discussed in this perspective. We also provide an overview of the key strategies for scientific and industrial applications with an eye on potential improvements for a sustainable future.

A vinylene-linked diketopyrrolopyrrole-based covalent organic framework for photocatalytic oxidation reactions

A vinylene-linked DPP-COF with an ultra-narrow bandgap of 1.06 eV was reported. This COF demonstrates high chemical stability and significant charge transfer properties, and was applied to the photooxidation of sulfides and tetrahydroisoquinolines, exhibiting exceptional photoactivities.

Design Principles for Enhancing Both Carrier Mobility and Stretchability in Polymer Semiconductors via Lewis Acid Doping

With the rise of skin-like electronics, devices are increasingly coming into close contact with the human body, creating a demand for polymer semiconductors (PSCs) that combine stretchability with reliable electrical performance. However, balancing mechanical robustness with high carrier mobility remains a challenge. To address this, tris(pentafluorophenyl)borane (BCF) for Lewis acid doping is proposed to improve charge mobility while enhancing stretchability by increasing structural disorder. Through systematic investigation, several key structural principles have been identified to maximize the effectiveness of BCF doping in stretchable PSCs. Notably, increasing the lamellar stacking distance and reducing crystallinity facilitate the incorporation of BCF into the alkyl side-chain regions, thereby enhancing both mobility and stretchability. Conversely, stronger Lewis base groups in the main chain negatively impact these improvements. These results demonstrate that with a small addition of BCF, a two-fold increase in carrier mobility is achieved while simultaneously enhancing the crack onset strain to 100%. Furthermore, doped PSCs exhibit stable mobility retention under repeated 30% strains over 1000 cycles. This method of decoupling carrier mobility from mechanical properties opens up new avenues in the search for high-mobility stretchable PSCs.

Conjugated Polymer-Based Photo-Crosslinker for Efficient Photo-Patterning of Polymer Semiconductors

Photo-patterning of polymer semiconductors using photo-crosslinkers has shown potential for organic circuit fabrication via solution processing techniques. However, the performance of patterning, including resolution (R), UV light exposure dose, sensitivity (S), and contrast (γ), remains unsatisfactory. In this study, a novel conjugated polymer based photo-crosslinker (PN3, Figure 1a) is reported for the first time, which entails phenyl-substituted azide groups in its side chains. Due to the potential π-π interactions between the conjugated backbone of PN3 and those of polymer semiconductors, PN3 exhibits superior miscibility with polymer semiconductors compared to the commonly used small molecule photo-crosslinker 4Bx (Figure 1a). Consequently, photo-patterning of polymer semiconductors with PN3 demonstrates improved performance with much lower UV light exposure dose, higher S and higher γ compared to 4Bx. By utilizing electron beam lithography, patterned arrays of polymer semiconductors with resolutions down to 500 nm and clearer edges are successfully fabricated using PN3. Furthermore, patterned arrays of PDPP4T, the p-type semiconductor (Figure 1b), after being doped, can function as source-drain electrodes for fabricating field-effect transistors (FETs) with comparable charge mobility and significantly lower sub-threshold swing value compared to those with gold electrodes.

Exceptional Field Effect and Negative Differential Conductance in Spiro-Conjugated Single-Molecule Junctions

The advancement of molecular electronics endeavors to build miniaturized electronic devices using molecules as the key building blocks by harnessing their internal structures and electronic orbitals. To date, linear planar conjugated or cross-conjugated molecules have been extensively employed in the fabrication of single-molecule devices, benefiting from their good conductivity and compatibility with electrode architectures. However, the development of multifunctional single-molecule devices, particularly those with unique charge transport properties, necessitates a more rigorous selection of molecular materials. Among different assortments of molecules suited for the construction of molecular circuits, Spiro-conjugated structures, specifically spirobifluorene derivatives, stand out as promising candidates due to their distinctive electronic properties. In this work, we focus on the charge transport characteristics of Spiro-conjugated molecules sandwiched between graphene nanogaps. Experiments reveal significant Coulomb blockade and distinct negative differential conductance effects. Beyond two-terminal device measurements, solid-state gate electrodes are utilized to create single-molecule transistors, successfully modulating the molecular energy levels to achieve an on/off ratio exceeding 1000. This endeavor not only offers valuable insights into the design and fabrication of future practical molecular devices, blessed with enhanced performance and functionality, but also presents a new paradigm for the investigation of fundamental physical phenomena.

Soft hydrogel semiconductors with augmented biointeractive functions

Hydrogels, known for their mechanical and chemical similarity to biological tissues, are widely used in biotechnologies, whereas semiconductors provide advanced electronic and optoelectronic functionalities such as signal amplification, sensing, and photomodulation. Combining semiconducting properties with hydrogel designs can enhance biointeractive functions and intimacy at biointerfaces, but this is challenging owing to the low hydrophilicity of polymer semiconductors. We developed a solvent affinity-induced assembly method that incorporates water-insoluble polymer semiconductors into double-network hydrogels. These semiconductors exhibited tissue-level moduli as soft as 81 kilopascals, stretchability of 150% strain, and charge-carrier mobility up to 1.4 square centimeters per volt per second. When they are interfaced with biological tissues, their tissue-level modulus enables alleviated immune reactions. The hydrogel's high porosity enhances molecular interactions at semiconductor-biofluid interfaces, resulting in photomodulation with higher response and volumetric biosensing with higher sensitivity.

Molecular-Scale Geometric Design: Zigzag-Structured Intrinsically Stretchable Polymer Semiconductors

Orienting intelligence and multifunction, stretchable semiconductors are of great significance in constructing next-generation human-friendly wearable electronic devices. Nevertheless, rendering semiconducting polymers mechanical stretchability without compromising intrinsic electrical performance remains a major challenge. Combining geometry-innovated inorganic systems and structure-tailored organic semiconductors, a molecular-scale geometric design strategy is proposed to obtain high-performance intrinsically stretchable polymer semiconductors. Originating from the linear regioregular conjugated polymer and corresponding para-modified near-linear counterpart, a series of zigzag-structured semiconducting polymers are developed with diverse ortho-type and meta-type kinking units quantitatively incorporated. They showcase huge edges in realizing stretchability enhancement for conformational transition, likewise with long-range π-aggregation and short-range torsion disorder taking effect. Assisted by additional heteroatom embedment and flexible alkyl-chain attachment, mechanical stretchability and carrier mobility could afford a two-way promotion. Among zigzag-structured species, o-OC8-5% with the initial field-effect mobility up to 1.92 cm2 V-1 s-1 still delivers 1.43 and 1.37 cm2 V-1 s-1 under 100% strain with charge transport parallel and perpendicular to the stretching direction, respectively, accompanied by outstanding performance retention and cyclic stability. This molecular design strategy contributes to an in-depth exploration of prospective intrinsically stretchable semiconductors for cutting-edge electronic devices.

In situ continuous hydrogen-bonded engineering for intrinsically stretchable and healable high-mobility polymer semiconductors

As a key component for wearable electronics, intrinsically stretchable and healable semiconducting polymers are scarce because carrier mobility is often reduced with increasing stretchability and self-healability. Here, we combine stepwise polymerization and thermal conversion to introduce in situ continuous hydrogen bonding sites in a polymer backbone without breaking the conjugation or introducing bulky softer side chains, benefiting the intrachain and interchain charge transport. We demonstrate that a regular sequence structure facilitated the formation of big nanofibers with a high degree of aggregation, providing the loose and porous thin film with simultaneously improved charge transport, stretchability, and self-healability. The mobility of damaged devices can be recovered to 81% after a healing treatment. Fully stretchable transistor based on the designed polymer exhibited a greatly enhanced mobility up to 1.08 square centimeters per volt per second under 100% strain, which is an unprecedented value and constitutes a major step for the development of intrinsically stretchable and healable semiconducting polymers.

Intrinsically stretchable fully π-conjugated polymer film via fluid conjugated molecular external-plasticizing for flexible light-emitting diodes

Fully π-conjugated polymers with rigid aromatic units are promising for flexible optoelectronic devices, but their inherent brittleness poses a challenge for achieving high-performance, intrinsically stretchable fully π-conjugated polymer. Here, we are establishing an external-plasticizing strategy using semiconductor fluid plasticizers (Z1 and Z2) to enhance the optoelectronic, morphological, and stretchable properties of fully π-conjugated polymer films for flexible light-emitting diodes. The synergistic effect of hierarchical structure and optoelectronic properties of Z1 in poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) films enable excellent stretchable deformability (~25%) and good conductivity. PLEDs based on F8BT/Z1 films show stable electroluminescence and efficiency under 15% stretch and 100 cycles at 10% strain, revealing outstanding stress tolerance. This strategy is also improving the stretchable properties of polymers like poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) and poly(2-methoxy-5(2'-ethyl)hexoxy-phenylenevinylene) (Super Yellow), demonstrating its general applicability. Therefore, this strategy can provide effective guidance for designing high-performance stretchable fully π-conjugated polymers films for flexible electronic devices.

Intrinsically Stretchable Organic Thermoelectric Polymers Enabled by Incorporating Fused-Ring Conjugated Breakers

While research on organic thermoelectric polymers is making significant progress in recent years, realization of a single polymer material possessing both thermoelectric properties and stretchability for the next generation of self-powered wearable electronics is a challenging task and remains an area yet to be explored. A new molecular engineering concept of "conjugated breaker" is employed to impart stretchability to a highly crystalline diketopyrrolepyrrole (DPP)-based polymer. A hexacyclic diindenothieno[2,3-b]thiophene (DITT) unit, with two 4-octyloxyphenyl groups substituted at the tetrahedral sp3-carbon bridges, is selected to function as the conjugated breaker that can sterically hinder intermolecular packing to reduce polymers' crystallinity. A series of donor-acceptor random copolymers is thus developed via polymerizing the crystalline DPP units with the DITT conjugated breakers. By controlling the monomeric DPP/DITT ratios, DITT30 reaches the optimal balance of crystalline/amorphous regions, exhibiting an exceptional power factor (PF) value up to 12.5 µW m-1 K-2 after FeCl3-doping; while, simultaneously displaying the capability to withstand strains exceeding 100%. More significantly, the doped DITT30 film possesses excellent mechanical endurance, retaining 80% of its initial PF value after 200 cycles of stretching/releasing at a strain of 50%. This research marks a pioneering achievement in creating intrinsically stretchable polymers with exceptional thermoelectric properties.

Improved Mobility-Stretchability Properties of Diketopyrrolopyrrole-Based Conjugated Polymers with Diastereomeric Conjugation Break Spacers

Stretchable conjugated polymers with conjugation break spacers (CBSs) synthesized via random terpolymerization have gained considerable attention because of their efficacy in modulating mobility and stretchability. This study incorporates a series of dianhydrohexitol diastereomers of isosorbide (ISB) and isomannide (IMN) units into the diketopyrrolopyrrole-based backbone as CBSs. It is found that the distorted CBS (IMN) improves the mobility-stretchability properties of the polymer with a highly coplanar backbone, whereas the extended CBS (ISB) enhances those of the polymer with a noncoplanar backbone. Additionally, the different configurations of ISB and IMN sufficiently affect the solid-state packing, aggregation capabilities, crystallographic parameters, and mobility-stretchability properties of the polymer. The IMN-based polymers exhibit the highest mobility of 1.69 cm2 V-1 s-1 and crystallinity retentions of (85.7, 78.6)% under 20% and 60% strains, outperforming their ISB-based or unmodified counterparts. The improvement is correlated with a robust aggregation capability. Furthermore, the CBS content affects aggregation behavior, notably affecting mobility. This result indicates that incorporating CBSs into the polymer can enhance backbone flexibility via movement and rotation of the CBS without affecting the crystalline regions.

Intrinsically Elastic Semiconductors through Aldehyde-Amine Polycondensation and Its Application on Stretchable Transistor

With the increasing demand for elastic electronics, as a crucial component, elastic semiconductors have been widely studied. However, there are some issues for the current preparation of elastic semiconductors, such as harsh reaction conditions, low atomic economic utilization, and complicated product separation and purification. Aldehyde-amine polycondensation is an important chemical reaction with the advantages of mild reaction conditions, high atomic-economic efficiency, and easy separation and purification. Herein, intrinsically elastic semiconductors are developed via aldehyde-amine polycondensation, including a semiconducting segment and an elastic segment. The resulting polymer containing 42.62 wt % soft segments exhibits excellent stretchability and mechanical reversibility, especially with a lower modulus. Interestingly, the carrier mobility displays up to 0.04 cm2·V-1·s-1, in the range of the fully conjugated reference polymer (0.1 cm2·V-1·s-1). In brief, this strategy provides important guiding principles for the development of intrinsically elastic polymer semiconductors.

Dynamics of Polyalkylfluorene Conjugated Polymers: Insights from Neutron Spectroscopy and Molecular Dynamics Simulations

The dynamics of the conjugated polymers poly(9,9-dioctylfluorene) (PF8) and poly(9,9-didodecylfluorene) (PF12), differing by the length of their side chains, is investigated in the amorphous phase using the temperature-dependent quasielastic neutron scattering (QENS) technique. The neutron spectroscopy measurements are synergistically underpinned by molecular dynamics (MD) simulations. The probe is focused on the picosecond time scale, where the structural dynamics of both PF8 and PF12 would mainly be dominated by the motions of their side chains. The measurements highlighted temperature-induced dynamics, reflected in the broadening of the QENS spectra upon heating. The MD simulations reproduced well the observations; hence, the neutron measurements validate the MD force fields, the adopted amorphous model structures, and the numerical procedure. As the QENS spectra are dominated by the signal from the hydrogens on the backbones and side chains of PF8 and PF12, extensive analysis of the MD simulations allowed the following: (i) tagging these hydrogens, (ii) estimating their contributions to the self-part of the van Hove functions and hence to the QENS spectra, and (iii) determining the activation energies of the different motions involving the tagged hydrogens. PF12 is found to exhibit QENS spectra broader than those of PF8, indicating a more pronounced motion of the didodecyl chains of PF12 as compared to dioctyl chains of PF8. This is in agreement with the outcome of our MD analysis: (i) confirming a lower glass transition temperature of PF12 compared to PF8, (ii) showing PF12 having a lower density than PF8, and (iii) highlighting lower activation energies of the motions of PF12 in comparison with PF8. This study helped to gain insights into the temperature-induced side-chain dynamics of the PF8 and PF12 conjugated polymers, influencing their stability, which could potentially impact, on the practical side, the performance of the associated optoelectronic active layer.

Nonhalogenated Solvent Processable and High-Density Photopatternable Polymer Semiconductors Enabled by Incorporating Hydroxyl Groups in the Side Chains

Polymer semiconductors hold tremendous potential for applications in flexible devices, which is however hindered by the fact that they are usually processed by halogenated solvents rather than environmentally more friendly solvents. An effective strategy to boost the solubility of high-performance polymer semiconductors in nonhalogenated solvents such as tetrahydrofuran (THF) by appending hydroxyl groups in the side chains is herein presented. The results show that hydroxyl groups, which can be easily incorporated into the side chains, can significantly improve the solubility of typical p- and n-types as well as ambipolar polymer semiconductors in THF. Meanwhile, the thin films of these polymer semiconductors from the respective THF solutions show high charge mobilities. With THF as the processing and developing solvents these polymer semiconductors with hydroxyl groups in the side chains can be well photopatterned in the presence of the photo-crosslinker, and the charge mobilities of the patterned thin films are mostly maintained by comparing with those of the respective pristine thin films. Notably, THF is successfully utilized as the processing and developing solvent to achieve high-density photopatterning with ≈82 000 device arrays cm-2 for polymer semiconductors in which hydroxyl groups are appended in the side chains.

Pre-Endcapping of Hyperbranched Polymers toward Intrinsically Stretchable Semiconductors with Good Ductility and Carrier Mobility

The advancement of semiconducting polymers stands as a pivotal milestone in the quest to realize wearable electronics. Nonetheless, endowing semiconductor polymers with stretchability without compromising their carrier mobility remains a formidable challenge. This study proposes a "pre-endcapping" strategy for synthesizing hyperbranched semiconducting polymers (HBSPs), aiming to achieve the balance between carrier mobility and stretchability for organic electronics. The findings unveil that the aggregates formed by the endcapped hyperbranched network structure not only ensure efficient charge transport but also demonstrate superior tensile resistance. In comparison to linear conjugated polymers, HBSPs exhibit substantially larger crack onset strains and notably diminished tensile moduli. It is evident that the HBSPs surpass their linear counterparts in terms of both their semiconducting and mechanical properties. Among HBSPs, HBSP-72h-2.5 stands out as the preeminent candidate within the field of inherently stretchable semiconducting polymers, maintaining 93% of its initial mobility even when subjected to 100% strain (1.41 ± 0.206 cm2 V-1 s-1). Furthermore, thin film devices of HBSP-72h-2.5 remain stable after undergoing repeated stretching and releasing cycles. Notably, the mobilities are independent of the stretching directions, showing isotropic charge transport behavior. The preliminary study makes this "pre-endcapping" strategy a potential candidate for the future design of organic materials for flexible electronic devices.

Effect of solvent quality and sidechain architecture on conjugated polymer chain conformation in solution

Conjugated polymers (CPs) are solution-processible for various electronic applications, where solution aggregation and dynamics could impact the morphology in the solid state. Various solvents and solvent mixtures have been used to dissolve and process CPs, but few studies have quantified the effect of solvent quality on the solution behavior of CPs. Herein, we performed static light scattering and small-angle X-ray scattering combined with molecular dynamics (MD) simulation to investigate CP solution behaviors with solvents of varying quality, including poly(3-alkylthiophene) (P3ATs) with various sidechain lengths from -C4H9 to -C12H25, poly[bis(3-dodecyl-2-thienyl)-2,2'-dithiophene-5,5'-diyl] (PQT-12) and poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-12). We found that chlorobenzene is a better solvent than toluene for various CPs, which was evident from the positive second virial coefficient A2 ranging from 0.3 to 4.7 × 10-3 cm3 mol g-2 towards P3ATs. For P3ATs in non-polar solvents, longer sidechains promote more positive A2, indicating a better polymer-solvent interaction, wherein A2 for toluene increases from -5.9 to 1.4 × 10-3 cm3 mol g-2, and in CB, A2 ranges from 1.0 to 4.7 × 10-3 cm3 mol g-2 when sidechain length increases from -C6H13 to -C12H25. Moreover, PQT-12 and PBTTT-12 have strong aggregation tendencies in all solutions, with an apparent positive A2 (∼0.5 × 10-3 cm3 mol g-2) due to multi-chain aggregates and peculiar chain folding. These solvent-dependent aggregation behaviors can be well correlated to spectroscopy measurement results. Our coarse-grained MD simulation results further suggested that CPs with long, dense, and branched sidechains can achieve enhanced polymer-solvent interaction, and thus enable overall better solution dispersion. This work provides quantitative insights into the solution behavior of conjugated polymers that can guide both the design and process of CPs toward next-generation organic electronics.

Microstructural Evolution of P(NDI2OD-T2) Films with Different Molecular Weight during Stretching Deformation

Conjugated polymers exhibit excellent electrical and mechanical properties when their molecular weight (Mw) is above the critical molecular weight (Mc). The microstructural changes of polymers under strain are crucial to establish a structure-performance relationship. Herein, the tensile deformation of P(NDI2OD-T2) is visualized, and cracks are revealed either along the (100) crystal plane of side chain packing or along the main chain direction which depends on the Mw is below or above the Mc. When Mw < Mc, the film cracks along the (100) plane under small strains. When Mw > Mc, the polymer chains first undergo stretch-induced orientation and then fracture along the main chain direction at large strains. This is attributed to the fact that the low Mw film exhibits large crystalline domains and the absence of interdomain connectivity, which are vulnerable to mechanical stress. In contrast, the high Mw film displays a nearly amorphous morphology with adequate entanglements, the molecular chains can endure stresses in the stretching direction to release substantial strain energy under greater mechanical deformation. Therefore, the film with Mw > Mc exhibits the optimal electrical and mechanical performances simultaneously, i.e., the electron mobility is retained under 100% strain and after 100 stretching-releasing cycles.

Multifunction-oriented high-mobility polymer semiconductors

Recent progress in multifunction-oriented high-mobility polymer semiconductors is profiled, with current challenges and future directions proposed in this perspective.

Intrinsically Stretchable and Healable Polymer Semiconductors

In recent decades, polymer semiconductors, extensively employed as charge transport layers in devices like organic field-effect transistors (OFETs), have undergone thorough investigation due to their capacity for large-area solution processing, making them promising for mass production. Research efforts have been twofold: enhancing the charge mobilities of polymer semiconductors and augmenting their mechanical properties to meet the demands of flexible devices. Significant progress has been made in both realms, propelling the practical application of polymer semiconductors in flexible electronics. However, integrating excellent semiconducting and mechanical properties into a single polymer still remains a significant challenge. This review intends to introduce the design strategies and discuss the properties of high-charge mobility stretchable conjugated polymers. In addition, another key challenge faced in this cutting-edge field is maintaining stable semiconducting performance during long-term mechanical deformations. Therefore, this review also discusses the development of healable polymer semiconductors as a promising avenue to improve the lifetime of stretchable device. In conclusion, challenges and outline future research perspectives in this interdisciplinary field are highlighted.

Aligned Conjugated Polymer Nanofiber Networks in an Elastomer Matrix for High-Performance Printed Stretchable Electronics

Conjugated polymer films are promising in wearable X-ray detection. However, achieving optimal film microstructure possessing good electrical and detection performance under large deformation via scalable printing remains challenging. Herein, we report bar-coated high-performance stretchable films based on a conjugated polymer P(TDPP-Se) and elastomer SEBS blend by optimizing the solution-processing conditions. The moderate preaggregation in solution and prolonged growth dynamics from a solvent mixture with limited dissolving capacity is critical to forming aligned P(TDPP-Se) chains/crystalline nanofibers in the SEBS phase with enhanced π-π stacking for charge transport and stress dissipation. The film shows a large elongation at break of >400% and high mobilities of 5.29 cm2 V-1 s-1 at 0% strain and 1.66 cm2 V-1 s-1 over 500 stretch-release cycles at 50% strain, enabling good X-ray imaging with a high sensitivity of 1501.52 μC Gyair-1 cm-2. Our work provides a morphology control strategy toward high-performance conjugated polymer film-based stretchable electronics.

Effect of Fluorination Position on the Crystalline Structure and Stretchability of Intrinsically Stretchable Polymer Semiconductors

A clear understanding of the structure-property relationship of intrinsically stretchable polymer semiconductors (ISPSs) is essential for developing high-performance polymer-based electronics. Herein, we investigate the effect of the fluorination position on the crystalline structure, charge-carrier mobility, and stretchability of polymer semiconductors based on a benzodithiophene-co-benzotriazole configuration. Although four different polymer semiconductors showed similar field-effect mobilities for holes (μ ≈ 0.1 cm2 V-1 s-1), polymer semiconductors with nonfluorinated backbones exhibited improved thin-film stretchability confirmed with crack onset strain (εc ≈ 20%-50%) over those of fluorinated counterparts (εc ≤ 10%). The enhanced stretchability of polymer semiconductors with a nonfluorinated backbone is presumably due to the higher face-on crystallite ratio and π-π stacking distance in the out-of-plane direction than those of the other polymer semiconductors. These results provide new insights into how the thin-film stretchability of polymer semiconductors can be improved by using precise molecular tailoring without deteriorating electrical properties.

Chain-Kinked Design: Improving Stretchability of Polymer Semiconductors through Nonlinear Conjugated Linkers

The manipulation of the polymer backbone structure has a profound influence on the crystalline behavior and charge transport characteristics of polymers. These strategies are commonly employed to optimize the performance of stretchable polymer semiconductors. However, a universal method that can be applied to conjugated polymers with different donor-acceptor combinations is still lacking. In this study, we propose a universal strategy to boost the stretchability of polymers by incorporating the nonlinear conjugated linker (NCL) into the main chain. Specifically, we incorporate meta-dibromobenzene (MB), characterized by its asymmetric linkage sites, as the NCL into the backbone of diketopyrrolopyrrole-thiophene-based (DPP-based) polymers. Our research demonstrates that the introduction of MB prompts chain-kinking, thereby disrupting the linearity and central symmetry of the DPP conjugated backbone. This modification reshapes the polymer conformation, decreasing the radius of gyration and broadening the free volume, which consequently adjusts the level of crystallinity, leading to a considerable increase in the stretchability of the polymer. Importantly, this method increases stretchability without compromising mobility and exhibits broad applicability across a wide range of donor-acceptor pair polymers. Leveraging this strategy, fully stretchable transistors were fabricated using a DPP polymer that incorporates 10 mol % of MB. These transistors display a mobility of approximately 0.5 cm2 V-1 s-1 and prove remarkably durable, maintaining 90% of this mobility even after enduring 1000 cycles at 25% strain. Overall, we propose a method to systematically control the main-chain conformation, thereby enhancing the stretchability of conjugated polymers in a widely applicable manner.

Achieving High Performance Stretchable Conjugated Polymers via Donor Structure Engineering

A backbone engineering strategy is developed to tune the mechanical and electrical properties of conjugated polymer semiconductors. Four Donor-Acceptor (D-A) polymers, named PTDPPSe, PTDPPTT, PTDPPBT, and PTDPPTVT, are synthesized using selenophene (Se), thienothiophene (TT), bithiophene (BT), and thienylenevinylenethiophene (TVT) as the donors and siloxane side chain modified diketopyrrolopyrrole (DPP) as acceptor. The influences of the donor structure on the polymer energy level, film morphology, molecular stacking, carrier transport properties, and tensile properties are all examined. The films of PTDPPSe show the best stretchability with crack-onset-strain greater than 100%, but the worst electrical properties with a mobility of only 0.54 cm2  V-1  s-1 . The replacement of the Se donor with larger conjugated donors, that is, TT, BT, and TVT, significantly improves the mobility of conjugated polymers but also leads to reduced stretchability. Remarkably, PTDPPBT exhibits moderate stretchability with crack-onset-strain ≈50% and excellent electrical properties. At 50% strain, it has a mobility of 2.37 cm2 V-1  s-1 parallel to the stretched direction, which is higher than the mobility of most stretchable conjugated polymers in this stretching state.

Hyperbranched Polymers for Organic Semiconductors

Hyperbranched polymers (HBPs) have attracted increasing attention owing to their distinct highly branched topological structures, resulting in unique properties and wide applications in organic semiconductors (OSCs). In this Review, recent progress in functional HBPs is outlined in the field of OSCs, including organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), dye-sensitized solar cells (DSSCs), and organic field effect transistors (OFETs), among others. Prospects of HBPs-based materials in OSCs are examined. The results revealed that multi-dimensional topologies not only regulate the electron (hole) transport but also adjust the film morphology, thereby affecting the efficiency and long life of organic electronic devices. Many studies showed the usefulness of HBPs as hole transport materials but reports dealing with n-type and ambipolar materials are still lacking. In addition, the interchain covalent bond in hyperbranched polymers could mitigate the damage caused by stretching, conducive to building stable flexible stretchable devices with long-term durability and good safety under harsh environmental conditions. Overall, the flexible stretchable design may enrich the applications of HBPs in organic semiconductors and provide new ideas for guiding the future design of functional organic semiconductor materials.