Yunfei Wang

Enabling green-solvent-processed large-area organic solar cells (OSCs) is of great significance to their industrialization. However, precisely controlling the temperature-dependent fluid mechanics and evaporation behavior of green solvents with high-boiling points is challenging. Controlling these parameters is essential to prevent the non-uniform distribution of active layer components and severe molecule aggregation, which collectively degrade the power conversion efficiency (PCE) of large-scale devices. In this study, we revealed that the temperature gradient distribution across a wet film is the root of the notorious Marangoni effect, which leads to the formation of a severely non-uniform active layer on a large scale. Thus, a rapid solidification strategy was proposed to accelerate the evaporation of toluene, a green solvent, at room temperature. This strategy simultaneously inhibits the Marangoni effect and …

The development of semiconducting polymers with good processability in green solvents and competitive electrical performance is essential for realizing sustainable large‐scale manufacturing and commercialization of organic electronics. A major obstacle is the processability‐performance dichotomy that is dictated by the lack of ideal building blocks with balanced polarity, solubility, electronic structures, and molecular conformation. Herein, through the integration of donor, quinoid and acceptor units, an unprecedented building block, namely TQBT, is introduced for constructing a serial of conjugated polymers. The TQBT, distinct in non‐symmetric structure and high dipole moment, imparts enhanced solubility in anisole—a green solvent—to the polymer TQBT‐T. Furthermore, PTQBT‐T possess a highly rigid and planar backbone owing to the nearly coplanar geometry and quinoidal nature of TQBT, resulting in …

The driving force behind the significant advancement of conductive polymer binders for lithium-ion batteries (LIBs) stems from the poor binding strength, limited mechanical properties, and absence of electronic conductivity of the commonly used nonconjugated polymer binder, poly(vinylidene fluoride) (PVDF). With a goal to induce stretchability and deformability to the otherwise brittle conjugated backbone, we report here dihexyl-substituted poly(3,4-propylenedioxythiophene)-based (PProDOT-Hx2-based) conjugated polymers wherein conjugation break spacers (CBS, T-X-T) of varying alkyl spacer lengths (X = 6, 8, and 10) and varying contents (5, 10, and 20%) have been randomly incorporated into the PProDOT backbone, generating a family of nine random PProDOT-CBS copolymers. Electrochemical characterization revealed that three out of the nine PProDOT-CBS polymers (5% T-6-T, 5% T-8-T, and 10% T-6 …

The use of inorganic nanofillers has been an effective method to improve high‐temperature capacitive performance of dielectric polymers, though there are unmet challenges such as undesirable organic–inorganic compatibility, and low efficiencies and energy densities. Herein, a surface functionalization strategy using covalent organic frameworks (COFs) is employed to address such challenges in realizing high‐performing polymer composites. Specifically, core–shell structured nanoparticles, where ZrO2 nanoparticles act as the core and a COF material forms the shell, are constructed and composited with the polyetherimide (PEI) matrix. The design leverages the high electron affinity (EA) of the outer COF shell to create energy traps, thereby capturing free charges and limiting electrical conduction. Concurrently, the low EA and wide bandgap of the ZrO2 core introduce energy barriers to impede charge injection …

Developing stretchable semiconducting polymers plays an essential role with the growing demand for electronic skins, wearable, and implanted devices, sensors, etc. Hydrogen bond, a dynamic bond (HB), was reported able to effectively improve the stretchability of semiconductors when introduced either in pure conjugated polymers (CPs) or elastomer matrix of CP/elastomer composites. In this work, we combined these two methods that we introduced amide groups into both DPPTVT CP (DPPTVT-A) and elastomer matrix (amide-polyisobutylene, PIB-A) to fabricate dual hydrogen bond-crosslinked DPPTVT-A/PIB-A composites, and carefully studied the non-covalent hydrogen bonding location effect on morphology, electrical and mechanical properties. Their non-hydrogen bonding counterparts, DPPTVT and PIB, were selected as comparative reference fabricating uni-HB-crosslinked composites DPPTVT-A/PIB …

The use of bioelectronic devices relies on direct contact with soft biotissues. For transistor-type bioelectronic devices, the semiconductors that need to have direct interfacing with biotissues for effective signal transduction do not adhere well with wet tissues, thereby limiting the stability and conformability at the interface. We report a bioadhesive polymer semiconductor through a double-network structure formed by a bioadhesive brush polymer and a redox-active semiconducting polymer. The resulting semiconducting film can form rapid and strong adhesion with wet tissue surfaces together with high charge-carrier mobility of ~1 square centimeter per volt per second, high stretchability, and good biocompatibility. Further fabrication of a fully bioadhesive transistor sensor enabled us to produce high-quality and stable electrophysiological recordings on an isolated rat heart and in vivo rat muscles.

Wearable devices benefit from the use of stretchable conjugated polymers (CPs). Traditionally, the design of stretchable CPs is based on the assumption that a low elastic modulus (E) is crucial for achieving high stretchability. However, this research, which analyzes the mechanical properties of 65 CP thin films, challenges this notion. It is discovered that softness alone does not determine stretchability; rather, it is the degree of entanglement that is critical. This means that rigid CPs can also exhibit high stretchability, contradicting conventional wisdom. To inverstigate further, the mechanical behavior, electrical properties, and deformation mechanism of two model CPs: a glassy poly(3‐butylthiophene‐2,5‐diyl) (P3BT) with an E of 2.2 GPa and a viscoelastic poly(3‐octylthiophene‐2,5‐diyl) (P3OT) with an E of 86 MPa, are studied. Ex situ transmission X‐ray scattering and polarized UV–vis spectroscopy revealed that …

The overarching goal of the proposed work was to set up a partnership between the University of Southern Mississippi (USM) and Oak Ridge National Laboratory (ORNL) to develop novel approaches to measure the backbone rigidity of conjugated polymers (CPs) and understand the critical role of sidechains on the backbone conformation and the materials macroscopic property. The backbone rigidity greatly influences the electronic properties of CPs, which ultimately determines the functionality and performance of these materials. Improvements in the electronic properties of CPs would allow for enhanced charge transport in semiconductor devices, improved photovoltaic performance, recycling of waste heat in thermoelectrics, and discovery of new phenomena that will enable the next generation of energy technologies. Although significant progress has been made to optimize the optical and electronic properties of CPs, largely through Edisonian methodologies, it remains a challenge to experimentally characterize conjugated backbone conformation (chain rigidity, torsion, planarity, and short-range order) and relate these to the fundamental optical and electronic properties (electronic coupling, charge transport, etc.). This has left fundamental gaps in our knowledge of the most basic structure/property relationships within these systems, precluded the study of fundamental physical phenomena, and constrained the design and realization of new electronic and device functionalities. Thus, the major goal of this work is to use novel deuteration methodologies via systematic synthetic approaches, and neutron scattering techniques to …

Physical blending conjugated polymers (CPs) with elastomers has been established as an effective method for enhancing the stretchability of semiconductors. However, predictable control of the morphology for incompatible polymer rubber blends remains a challenge. In this work, we demonstrated the control of phase separation size of CP/elastomer composites by strategically controlling the location sites of H-bonding functional groups in CPs and elastomers, while investigating their effects on mechanical and electrical properties. We incorporated amide functional groups into a DPP-based semiconducting polymer (DPPTVT-A) and polyisobutylene-based elastomer (PIB-A) to enable inter- and intraphase hydrogen bonding (H-bonding) cross-links within CP/elastomer composites. Along with their nonamide counterparts, we fabricated four different CP/elastomer composites, DPPTVT-A/PIB-A, DPPTVT-A/PIB …

Introducing hydrogen bonding structures into semiconducting polymers is an effective method to enhance the intra/interchain interactions and improve the overall performance of the polymer. In this study, diketopyrrolopyrrole (DPP)-based random copolymers with quadruple hydrogen bonding in the backbone are constructed by the copolymerization of a rationally designed ring-like tetrahydrogen-bonded ureidopyrimidinone (UPy) with alkyl chain-substituted DPP using a new design strategy via intramolecular hydrogen bonding. Specifically, ring-like UPy structures with different ratios were introduced into DPP-based conjugated polymers by the Stille coupling. The electrical and mechanical properties of the resulting series polymers were characterized before and after stretching. The copolymer’s tensile properties were improved owing to the introduction of the ring-like UPy unit, with 27.9% mobility retention under …

A solvent-less and additive-free approach was developed for the cross-linking of π-conjugated polymers through the formation of polydiacetylene (PDA) cross-links. Different ratios of conjugation-breaking spacers incorporating 1,3-butadiyne motifs were inserted into semicrystalline diketopyrrolopyrrole-based polymers and reacted under UV light to trigger a topochemical photopolymerization. Upon photo-cross-linking, the formation of PDA cross-links was confirmed by Raman spectroscopy, and the resulting materials were further characterized through various techniques including Fourier transform infrared spectroscopy, atomic force microscopy, X-ray scattering, and UV–vis spectroscopy to evaluate their photophysical and optical properties. Furthermore, the mechanical properties of the PDA-containing semiconducting materials were evaluated via quantitative nanomechanical mapping, which confirmed that an …

Semiconductors with both high stretchability and self‐healing capability are highly desirable for various wearable devices. Much progress has been achieved in designing highly stretchable semiconductive polymers or composites. The demonstration of self‐healable semiconductive composite is still rare. Here, an extremely soft, highly stretchable, and self‐healable hydrogen bonding cross‐linked elastomer, amide functionalized‐polyisobutylene (PIB‐amide) is developed, to enable a self‐healable semiconductive composite through compounding with a high‐performance conjugated diketopyrrolopyrrole (DPP‐T) polymer. The composite, consisting of 20% DPP‐T and 80% PIB‐amide, shows record high crack‐onset strain (COS ≈1500%), extremely low elastic modulus (E≈1.6 MPa), and unique ability to spontaneously self‐heal atroom temperature within 5 min. Unlike previous works, these unique composite …

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 …

Correction for 'Asymmetric side-chain engineering in semiconducting polymers: a platform for greener processing and post-functionalization of organic electronics' by Madison Mooney et al., Polym. Chem., 2023, https://doi.org/10.1039/d2py01244h.

Polymer semiconductors (PSCs) are essential active materials in mechanically stretchable electronic devices. However, many exhibit low fracture strain due to their rigid chain conformation and the presence of large crystalline domains. Here, a PSC/elastomer blend, poly[((2,6‐bis(thiophen‐2‐yl)‐3,7‐bis(9‐octylnonadecyl)thieno[3,2‐b]thieno[2′,3′:4,5]thieno[2,3‐d]thiophene)‐5,5′‐diyl)(2,5‐bis(8‐octyloctadecyl)‐3,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,4‐dione)‐5,5′‐diyl]] (P2TDPP2TFT4) and polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (SEBS) are systematically investigated. Specifically, the effects of molecular weight of both SEBS and P2TDPP2TFT4 on the resulting blend morphology, mechanical, and electrical properties are explored. In addition to commonly used techniques, atomic force microscopy‐based nanomechanical images are used to provide additional insights into …

Blending semiconductor polymers (SPs) with insulator polymers (IPs) is an effective strategy for preparing high-performance stretchable electronics. The key is the continuity of the semiconductor structure in the blend films, so the precise regulation of phase separation is the major challenge. Here, two key strategies that influence blend films were systematically investigated, including optimizing the solution-processable technique and controlling the semiconductor molecular weight (labeled LSP for 23.5 kDa, MSP for 108.5 kDa, and HSP for 222.6 kDa). Compared to the spin-coated (SC) films, the assembly on water-surface (AOW) films have uniform morphology, ordered microstructure, and better charge transport properties. During the formation of AOW films, SPs and IPs tend to move toward air and water, respectively, yielding a vertical phase separation structure. Moreover, a proportion of SPs are embedded in …

Organic semiconductors with high-spin ground states are fascinating because they could enable fundamental understanding on the spin-related phenomenon in light element and provide opportunities for organic magnetic and quantum materials. Although high-spin ground states have been observed in some quinoidal type small molecules or doped organic semiconductors, semiconducting polymers with high-spin at their neutral ground state are rarely reported. Here we report three high-mobility semiconducting polymers with different spin ground states. We show that polymer building blocks with small singlet-triplet energy gap (ΔES-T) could enable small ΔES-T gap and increase the diradical character in copolymers. We demonstrate that the electronic structure, spin density, and solid-state interchain interactions in the high-spin polymers are crucial for their ground states. Polymers with a triplet ground state (S …

The morphological stability of an organic photovoltaic (OPV) device is greatly affected by the dynamics of donors and acceptors occurring near the device's operational temperature. These dynamics can be quantified by the glass transition temperature (Tg) of conjugated polymers (CPs). Because flexible side chains possess much faster dynamics, the cleavage of the alkyl side chains will reduce chain dynamics, leading to a higher Tg. In this work, the Tgs for CPs are systematically studied with controlled side chain cleavage. Isothermal annealing of polythiophenes featuring thermally cleavable side chains at 140 °C, is found to remove more than 95% of alkyl side chains in 24 h, and raise the backbone Tg from 23 to 75 °C. Coarse grain molecular dynamics simulations are used to understand the Tg dependence on side chain cleavage. X‐ray scattering indicates that the relative degree of crystallization remains …

Polymer semiconductors have been widely studied as an important component of stretchable electronic devices. However, most stretchable polymer semiconductors suffer from different degrees of charge mobility degradation at high strain. Here, we report a novel side chain engineering strategy to realize stretch-induced enhancement of molecular orientation and charge transport in donor–acceptor conjugated polymers. Specifically, hybrid siloxane-based side chains wifth different silicon chain lengths were grafted onto a backbone of poly-diketo-pyrrolopyrrole-selenophene (PTDPPSe). The charge mobility can be enhanced with an appropriate increase of the silicon chain length. Most importantly, increasing the silicon chain length resulted in significant improvement of stretchability, including decreasing elastic modulus and increasing fracture strain. Interestingly, charge mobilities parallel to the stretching direction …

In article number 2206161, Jason D. Azoulay and co-workers demonstrate that long-range π-correlations within a solution-processed high-spin conjugated polymer provide robust spin-centers, intermolecular ferromagnetic exchange interactions, and anisotropic spin ordering. This new approach toward practically applicable metal-free magnetism opens new opportunities for emerging technologies that integrate spin, magnetic, and quantum mechanical effects and operate at room temperature.

Despite having favorable optoelectronic and thermomechanical properties, the wide application of semiconducting polymers still suffers from limitations, particularly with regards to their processing in solution which necessitates toxic chlorinated solvents due to their intrinsic low solubility in common organic solvents. This work presents a novel greener approach to the fabrication of organic electronics without the use of toxic chlorinated solvents. Low‐molecular‐weight non‐toxic branched polyethylene (BPE) is used as a solvent to process diketopyrrolopyrrole‐based semiconducting polymers, then the solvent‐induced phase separation (SIPS) technique is adopted to produce films of semiconducting polymers from solution for the fabrication of organic field‐effect transistors (OFETs). The films of semiconducting polymers prepared from BPE using SIPS show a more porous granular morphology with preferential edge …

Understanding molecular design rules for stretchable polymer semiconductors is important for enabling next generation stretchable electronic circuits. To simultaneously improve both electrical properties and mechanical stretchability, a design strategy is reported in introducing conjugated rigid fused‐rings with bulky side groups in semiconducting polymers. In this work, the understanding of this design concept is improved by systematically investigating the effect of different types of bulky side groups asymmetrically substituted on conjugated polymer semiconductor backbones. Specifically, four types of side groups are investigated, including naphthalene (NaPh), biphenyl (PhPh), thienylphenyl (ThPh), and alkylphenyl (C4Ph), asymmetrically substituted on benzodithiophene units, namely asy‐BDT. With the four types of side groups installed on BDT‐containing conjugated polymers in an asymmetrical fashion, it is …

Organic electrochemical transistors (OECTs) have shown great potential in bioelectronics and neuromorphic computing. However, the low performance of n-type OECTs impedes the construction of complementary-type circuits for low-power-consumption logic circuits and high-performance sensing. Compared with their p-type counterparts, the low electron mobility of n-type OECT materials is the primary challenge, leading to low μC* and slow response speed. Nevertheless, no successful method has been reported to address the issue. Here, we find that the charge carrier mobility of n-type OECTs can be significantly enhanced by redistributing the polarons on the polymer backbone. As a result, 1 order of magnitude higher electron mobility is achieved in a new polymer, P(gPzDPP-CT2), with a simultaneously enhanced μC* value and faster response speed. This work reveals the important role of polaron distribution …

Indacenodithiophene (IDT) copolymers are a class of conjugated polymers that have limited long-range order and high hole mobilities, which makes them promising candidates for use in deformable electronic devices. Key to their high hole mobilities is the coplanar monomer repeat units within the backbone. Poly(indacenodithiophene-benzothiadiazole) (PIDTC16-BT) and poly(indacenodithiophene-thiapyrollodione) (PIDTC16-TPDC1) are two IDT copolymers with planar backbones, but they are brittle at low molecular weight and have unsuitably high elastic moduli. Substitution of the hexadecane (C16) side chains of the IDT monomer with isocane (C20) side chains was performed to generate a new BT-containing IDT copolymer: PIDTC20-BT. Substitution of the methyl (C1) side chain on the TPD monomer for an octyl (C8) and 6-ethylundecane (C13B) afford two new TPD-containing IDT copolymers named PIDT …

To date, high-performance organic electrochemical transistors (OECTs) have mostly been based on polythiophene systems. Donor–acceptor (D–A) conjugated polymers are expected to be promising materials for OECTs owing to their high mobility and comparatively low crystallinity (good for ion diffusion). However, the OECT performance of D–A polymers lags far behind that of the polythiophenes. Here we synergistically engineered the backbone and side chain of a series of diketopyrrolopyrrole (DPP)-based D–A polymers and found that redox potential, molecular weight, solution processability, and film microstructures all have a severe impact on their performance. After systematic engineering, P(bgDPP-MeOT2) exhibited the best figure-of-merit (μC*) of 225 F cm−1 V−1 s−1, amongst the highest performance of the reported D–A polymers. Besides, the DPP polymers exhibited high hole mobility of over 1.6 cm2 V …

Organic semiconducting polymers are exciting materials for electronic applications because of their good mechanical and optoelectronic properties. A major advantage of organic semiconductors is their solution processability. This allows access to a variety of simple and cost-effective device fabrication methods compared to the expensive, high-temperature processing methods required for silicon-based electronics. However, these materials often have low solubility, which limits their processing to toxic halogenated solvents. Also, their limited solubility often leads to interfacial mixing during device fabrication. This work explores the incorporation of environmentally friendly carbohydrate side chains in conjugated polymers to enhance processability in eco-friendly solvents. Moreover, a mild postprocessing treatment was designed to enable solvent resistance. Isoindigo-based polymers with varied ratios of acetyl …

Performed through side-chain engineering or by incorporating intramolecular locking units, the directionality and dynamic nature of noncovalent interactions are particularly attractive for the design of novel semiconducting materials in a wide variety of applications. This work investigates the nature and position of hydrogen bonding (intra- versus intermolecular), with the objective of developing a rational approach to the design of new semiconducting materials with improved properties in the solid state. To control the polymer chains’ self-assembly, a π-conjugated polymer incorporating a moiety capable of generating intramolecular hydrogen bonding is evaluated against a polymer that allows for intermolecular hydrogen bonding. Characterization through various techniques, optical spectroscopies, grazing incidence wide-angle x-ray scattering, and solution small-angle neutron scattering showed that intramolecular …

Polymer semiconductors have shown distinct promise for the development of human-integrated electronics, owing to their solution processability and mechanical softness. However, numerous functional properties required for this application domain face synthetic challenges to being conveyed onto conjugated polymers and thus combined with efficient charge-transport properties. Here, we develop a "click-to-polymer" (CLIP) synthesis strategy for conjugated polymers, which uses a click reaction for the facile and versatile attachment of diverse types of functional units to a pre-synthesized conjugated-polymer precursor. With four types of functional groups, we show that functionalized polymers from this CLIP method can still retain good charge-carrier mobility. We take two realized polymers to showcase a photopatternable property and a biochemical sensing function, both of which advance the state of the art of …

A series of conjugated polymers on the basis of diketopyrrolopyrrole and thienothiophene with different lengths of linear hybrid siloxane-terminal side chains were designed and synthesized. The number of silicon atoms in the side chains was 3, 5, and 7 (PTDPPTT-Si-3, PTDPPTT-Si-5, and PTDPPTT-Si-7, respectively, with two accompanying reference polymers, PTDPPTT-Ref-1 and PTDPPTT-Ref-2). Compared with PTDPPTT-Si-3, PTDPPTT-Si-5 and PTDPPTT-Si-7 had longer siloxane-terminal groups, which allowed them to maintain higher solution processability and excellent mobilities of 2.44 and 2.18 cm–2 V–1 s–1, respectively. In addition, the extended siloxane segment has high flexibility, which provides a good opportunity to improve the mechanical properties of rigid conjugated polymers. PTDPPTT-Si-7 exhibited excellent ductility and a low tensile modulus of 108 ± 21 MPa and retained 80% of its initial …

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 …