High-mobility Polymer Research Articles

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.

Optimized Incorporation of Furan into Diketopyrrolopyrrole-Based Conjugated Polymers for Organic Field-Effect Transistors.

Flexible electronics have received considerable attention in the past decades due to their promising application in rollable display screens, wearable devices, implantable devices, and other electronic applications. In particular, conjugated polymers are favored for flexible electronics due to their mechanical flexibility and potential for solution-processed fabrication techniques, such as blade-coating, roll-to-roll printing, and high-throughput printing allowing for high-performance transistor devices. Thiophene is the prevailing conjugated unit to construct these conjugated polymers due to its favorable electronic properties. On the other hand, furans are among the few conjugated moieties that are easily derived from bio renewable resources. To promote sustainability, we selectively introduced furan into the conjugated backbone of a high-mobility polymer scaffold and systematically studied the effect on the microstructure and charge transport. We show that partially and selectively replacing thiophene units with furan can yield nearly comparable performance compared to the all-thiophene polymer. This strategy offers an improvement in the sustainability of the polymer by incorporating bio-sourced furan without sacrificing the high-performance characteristics. Meanwhile, polymers with incorrect or complete furan incorporation show reduced mobilities. This work serves to develop coherent structure-morphology-performance relationships; such knowledge will establish guidelines for the future development of sustainable, furan-based conjugated materials.

Reducing residual stress in photopolymerized composites by grafting high-mobility polymer chains onto the filler-matrix interface

3D/4D printing of thermosets, composites and hydrogels, lithographic procedures and dental resins are important examples of applications that rely on light-driven polymerization supported on substrates. Adhesion between the polymer and substrate during photopolymerization (and even between printed layers) can restrict the usual polymerization shrinkage, leading to the generation of residual stresses. These residual stresses can result in poor-quality products due to the presence of cracks and occurrence of warpage. In this work, silica nanoparticles were incorporated into photopolymerizable dimethacrylate based networks. These nanoparticles had their surface modified by grafting polymer chains with high mobility at usual room temperatures (low glass transition temperature polymer) and with high affinity towards the polymer matrix in order to test the hypothesis that these high-mobility chains could be helpful in dissipating stress and energy generated during photopolymerization in conditions in which the polymerization shrinkage is restricted. The nanoparticles and composites were analyzed via: electron microscopy (SEM), thermal analysis and mechanical bending tests. The evolution of the monomer-to-polymer conversion during photopolymerization was monitored using real-time infrared (FTIR) spectroscopy. To determine the residual stress generated by the polymerization at restricted contraction conditions, a universal mechanical testing machine was adapted and used. The results showed that silica nanoparticles with grafted high-mobility polymer chains that were able to interpenetrate and interact with the dimethacrylate based networks led to the production of composites having higher mechanical properties and lower polymerization stresses than composites containing only silanized nanoparticles and nanoparticles having immiscible polymer grafts towards the dimethacrylate based network. Results indicate that the modifications of the interface of composites developed in this work can be useful in the formulation of materials with improved mechanical properties and stability regarding polymerization shrinkage and residual stress that can lead to higher-quality products obtained in processes that employ light-driven polymerization supported on substrates or that occur on sequential polymerized layers, such as 3D/4D printing, lithography and in dental applications.

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.

Low-Temperature Alignment of Conjugated Polymers by Plasticizer-Aided Physical Rubbing.

Rubbing-induced alignment of conjugated polymers issystematically investigated in terms of intra- and inter-molecular interaction. Various polymer films with a broad range of polymer chain rigidity arerubbed, and the degree of polymer chain alignment isquantitatively characterized. The rubbing technique effectively aligns crystalline domains in conjugated polymer films when the temperature approaches the critical rubbing temperature ( ), at which the rearrangement and the slip of polymer chains are possible. A polymer with significant intra-/inter-molecular interactions exhibits higher , though quantitative analysis reveals an intermediately aligned state at temperature Tr ' lower than . This state originates from polymer chain aggregation in an amorphous domain. The intermediately aligned state can be controlled by plasticizer, which enables low-temperature alignment of high-mobility polymer film by reducing Tr ' to near 100 °C, increases the crystallinity, and improves the alignment effect at this state comparable to that of the completely aligned state obtained at extremely high temperatures.

A Semi-Crystalline Polymer Semiconductor with Thin Film Stretchability Exceeding 200.

Despite the emerging scientific interest in polymer-based stretchable electronics, the trade-off between the crystallinity and stretchability of intrinsically stretchable polymer semiconductors-charge-carrier mobility increases as crystallinity increases while stretchability decreases-hinders the development of high-performance stretchable electronics. Herein, a highly stretchable polymer semiconductor is reported that shows concurrently improved thin film crystallinity and stretchability upon thermal annealing. The polymer thin films annealed at temperatures higher than their crystallization temperatures exhibit substantially improved thin film stretchability (> 200%) and hole mobility (≥ 0.2cm2 V-1 s-1 ). The simultaneous enhancement of the crystallinity and stretchability is attributed to the thermally-assisted structural phase transition that allows the formation of edge-on crystallites and reinforces interchain noncovalent interactions. These results provide new insights into how the current crystallinity-stretchability limitation can be overcome. Furthermore, the results will facilitate the design of high-mobility stretchable polymer semiconductors for high-performance stretchable electronics.

Tough Glass with Mechanical Bonding Network Anchored by High-Mobility Polymers

A series of mechanically interlocked supramolecular glasses were prepared from a bio-based cyclic oligosaccharide with small amounts of polymer. The rigid glassy materials were readily thermo-moldable, and their mechanical properties were tuned by the substituents on the oligosaccharide. In the presence of even small amounts (<18 wt %) of polymer, fragile oligosaccharide derivatives turned into tough bio-based plastics, as long as the polymer penetrated through the cyclic molecules. A small difference in acyl substituents on the ring components resulted in a significant difference in the mechanical properties. Bulkier substituents monotonically decreased Young’s modulus and the glass transition temperature (Tg), indicating the predominance of interactions between ring components that maintain the material framework. However, the toughness dramatically changed, independent of the interactions, forming two glasses with the same Young’s modulus and Tg into different materials: brittle and ductile. A clear difference between brittle and ductile glasses was observed in their confined polymer mobility. Analysis of the dynamics revealed that the higher mobility of the polymer was maintained in the material frameworks of ductile glasses compared with that of brittle glasses, whereas a comparable glass prepared from a mixture of the two components of ductile glass was very fragile. These results suggest the necessity of a mechanical bonding network formed by high-mobility polymers so that the confined polymers can work as an anchor rapidly in response to crack formation in the framework

Fluorinated Benzothiadiazole-based polymers with chalcogenophenes for organic field-effect transistors

The effect of incorporating chalcogenophene comonomers, namely, furan, thiophene, and selenophene, on the optoelectrical properties of cyclopentadithiophene-based polymers (P1, P2, and P3, respectively) for organic field-effect transistors is reported. The optical, electrical, and morphological properties of the P1, P2, and P3 are investigated. Compared to the other polymers, the P2 showed the highest crystallinity with the shortest π–π stacking distance ( d π–π ≈ 3.58 Å) and the longest crystalline length ( L c ≈ 40 Å), as confirmed by two-dimensional grazing incidence wide-angle X-ray diffraction. However, P3 had the highest hole mobility ( μ = 0.25 cm 2 /V-s), which is higher than P1 ( μ = 0.06 cm 2 /V-s) and P2 ( μ = 0.20 cm 2 /V-s). The relatively lower mobility of the P2 than of the P3 is attributed to its island-like crystalline domains, confirmed by atomic force microscopy results and the edge-on dominant orientation. Our findings suggest a new design guideline for developing high-mobility π-conjugated polymers. • We first address the importance of size of substituted atoms in determining optoelectronic properties and thin film crystallinity of the FBT-based polymers. • The influence of chalcogenophene atom substitution on optoelectrical properties of the FBT-based polymers was thorough investigated. • Combining a highly-crystallized molecular packing with effective morphologies led to the best hole mobilities of 0.25 cm 2 V −1 s −1 for P3.

An Investigation of the Thermal Transitions and Physical Properties of Semiconducting PDPP4T:PDBPyBT Blend Films.

This work focuses on the study of thermal and physical properties of thin polymer films based on mixtures of semiconductor polymers. The materials selected for research were poly [2,5-bis(2-octyldodecyl)-pyrrolo [3,4-c]pyrrole-1,4(2H,5H)-dione-3,6-diyl)-alt-(2,2';5',2″;5″,2'''-quater-thiophen-5,5'''-diyl)]-PDPP4T, a p-type semiconducting polymer, and poly(2,5-bis(2-octyldodecyl)-3,6-di(pyridin-2-yl)-pyrrolo [3,4-c]pyrrole-1,4(2H,5H)-dione-alt-2,2'-bithiophene)-PDBPyBT, a high-mobility n-type polymer. The article describes the influence of the mutual participation of materials on the structure, physical properties and thermal transitions of PDPP4T:PDBPyBT blends. Here, for the first time, we demonstrate the phase diagram for PDPP4T:PDBPyBT blend films, constructed on the basis of variable-temperature spectroscopic ellipsometry and differential scanning calorimetry. Both techniques are complementary to each other, and the obtained results overlap to a large extent. Our research shows that these polymers can be mixed in various proportions to form single-phase mixtures with several thermal transitions, three of which with the lowest characteristic temperatures can be identified as glass transitions. In addition, the RMS roughness value of the PDPP4T:PDBPyBT blended films was lower than that of the pure materials.

Tough-interface-enabled stretchable electronics using non-stretchable polymer semiconductors and conductors.

Semiconducting polymer thin films are essential elements of soft electronics for both wearable and biomedical applications1-11. However, high-mobility semiconducting polymers are usually brittle and can be easily fractured under small strains (<10%)12-14. Recently, the improved intrinsic mechanical properties of semiconducting polymer films have been reported through molecular design15-18 and nanoconfinement19. Here we show that engineering the interfacial properties between a semiconducting thin film and a substrate can notably delay microcrack formation in the film. We present a universal design strategy that involves covalently bonding a dissipative interfacial polymer layer, consisting of dynamic non-covalent crosslinks, between a semiconducting thin film and a substrate. This enables high interfacial toughness between the layers, suppression of delamination and delocalization of strain. As a result, crack initiation and propagation are notably delayed to much higher strains. Specifically, the crack-onset strain of a high-mobility semiconducting polymer thin film improved from 30% to 110% strain without any noticeable microcracks. Despite the presence of a large mismatch in strain between the plastic semiconducting thin film and elastic substrate after unloading, the tough interface layer helped maintain bonding and exceptional cyclic durability and robustness. Furthermore, we found that our interfacial layer reduces the mismatch of thermal expansion coefficients between the different layers. This approach can improve the crack-onset strain of various semiconducting polymers, conducting polymers and even metal thin films.

Mechanical Properties of Organic Electronic Polymers on the Nanoscale (Adv. Electron. Mater. 3/2022)

High Mobility Polymers In article number 2101019, Deepak Venkateshvaran and colleagues present how the surface nanomechanical texture of high mobility polymers used for organic electronics is quantified together with their depth-dependent viscoelastic response. Measured data of the nanomechanical properties in a well-known organic semiconducting polymer is presented; blue represents the homogeneous Young's modulus within polymer grains, red represents grain boundary moduli, and topography represents modulus strength.

14GHz Schottky Diodes Using a p-Doped Organic Polymer.

The low carrier mobility of organic semiconductors and the high parasitic resistance and capacitance often encountered in conventional organic Schottky diodes hinder their deployment in emerging radio frequency (RF) electronics. Here, these limitations are overcome by combining self-aligned asymmetric nanogap electrodes (≈25nm) produced by adhesion lithography, with a high mobility organic semiconductor, and RF Schottky diodes able to operate in the 5G frequency spectrum are demonstrated. C16 IDT-BT is used, as the high hole mobility polymer, and the impact of p-doping on the diode performance is studied. Pristine C16 IDT-BT-based diodes exhibit maximum intrinsic and extrinsic cutoff frequencies (fC ) of >100and 6GHz, respectively. This extraordinary performance is attributed to the planar nature of the nanogap channel and the diode's small junction capacitance (<2pF). Doping of C16 IDT-BT with the molecular p-dopant C60 F48 improves the diode's performance further by reducing the series resistance resulting to intrinsic and extrinsic fC of >100and ≈14GHz respectively, while the DC output voltage of an RF rectifier circuit increases by a tenfold. Ourwork highlights the importance of the planar nanogap architecture and paves the way for the use of organic Schottky diodes in large-area RF electronics of the future.

Unraveling the Molar Mass Dependence of Shearing-Induced Aggregation Structure of a High-Mobility Polymer Semiconductor.

Aggregation-structure formation of conjugated polymers is a fundamental problem in the field of organic electronics and remains poorly understood. Herein, the molar mass dependence of the aggregation structure of a high-mobility conjugated copolymer (TDPP-Se) comprising thiophene-flanked diketopyrrolopyrrole and selenophene is thoroughly shown. Five batches of TDPP-Se are prepared with the number-average molecular weights (Mn ) varied greatly from 21 to 135kg mol-1 . Small-angle neutron scattering and transmission electron microscopy are combined to probe the solution structure of these polymers, consistently using a deuterated solvent. All the polymers adopt 1D rod-like aggregation structures and the radius of the 1D rods is not sensitive to the Mn , while the length increases monotonically with Mn . By utilizing the ordered packing of the aggregated structure in solution, a highly aligned and ordered film is prepared and, thereafter, a reliable hole mobility of 13.8 cm2 V-1 s-1 is realized in organic thin-film transistors with the moderate Mn batch via bar coating. The hole mobility is among the highest values reported for diketopyrrolopyrrole-based polymers. This work paves the way to visualize the real aggregated structure of polymer semiconductors in solution and sheds light on the microstructure control of high-performance electronic devices.

Wafer-scale integration of stretchable semiconducting polymer microstructures via capillary gradient

Organic semiconducting polymers have opened a new paradigm for soft electronics due to their intrinsic flexibility and solution processibility. However, the contradiction between the mechanical stretchability and electronic performances restricts the implementation of high-mobility polymers with rigid molecular backbone in deformable devices. Here, we report the realization of high mobility and stretchability on curvilinear polymer microstructures fabricated by capillary-gradient assembly method. Curvilinear polymer microstructure arrays are fabricated with highly ordered molecular packing, controllable pattern, and wafer-scale homogeneity, leading to hole mobilities of 4.3 and 2.6 cm2 V−1 s−1 under zero and 100% strain, respectively. Fully stretchable field-effect transistors and logic circuits can be integrated in solution process. Long-range homogeneity is demonstrated with the narrow distribution of height, width, mobility, on-off ratio and threshold voltage across a four-inch wafer. This solution-assembly method provides a platform for wafer-scale and reproducible integration of high-performance soft electronic devices and circuits based on organic semiconductors.

High-Performance Organic Phototransistors Based on D18, a High-Mobility and Unipolar Polymer

Organic optoelectronics has progressed excitingly in recent years, mainly due to the innovation of donor and acceptor systems. Organic photodetectors based on novel semiconductor materials and well-designed device architectures have also been reported with improved device performance. However, most of them were photodiodes, and it is challenging to integrate them into the well-established readout circuits. Organic phototransistors are mainly based on the hybrid strategy, composed of either hybrid films or multilayer device structures, which complicates charge transfer and charge transport. Most of the organic devices also suffer from poor stability. In this work, we introduce a recently developed p-type copolymer, D18, to fabricate high-performance phototransistors. D18 possesses excellent charge generation, high mobility, and unipolar charge transport, which fulfill the generic design rule of organic phototransistors. The optimized phototransistors based on D18 exhibited extremely low dark current (∼10 pA) and noise (∼10 fA/Hz1/2), a high detectivity of 4 × 1013 Jones, a swift response of <5 ms, and excellent device stability. We also demonstrated flexible phototransistors with decent performance metrics, indicating great potential for next-generation solution-processed photodetectors and flexible electronic devices.

Highly Stable Inverted CdSe/ZnS-Based Light-Emitting Diodes by Nonvacuum Technique ZTO as the Electron-Transport Layer

CdSe/ZnS quantum dots (QDs) have attracted great consideration from investigators owing to their excellent photo-physical characteristics and application in quantum dot light-emitting diodes (QD-LEDs). The CdSe/ZnS-based inverted QD-LEDs structure uses high-quality semiconductors electron transport layers (ETLs), a multilayered hole transporting layers (HTLs). In QD-LED, designing a device structure with a minimum energy barrier between adjacent layers is very important to achieve high efficiency. A high mobility polymer of poly (9,9-dioctylfluorene-co-N-(4-(3-methylpropyl)) diphenylamine (TFB) was doped with 4,4′-bis-(carbazole-9-yl) biphenyl (CBP) with deep energy level to produce composite TFB:CBP holes to solve energy mismatch (HTL). In addition, we also improved the QD-LED device structure by using zinc tin oxide (ZTO) as ETL to improve device efficiency. The device turn-on voltage Vt (1 cd m−2) with ZTO ETL reduced from 2.4 V to 1.9 V significantly. Furthermore, invert structure devices exhibit luminance of 4296 cd m−2, current-efficiency (CE) of 7.36 cd A−1, and external-quantum efficiency (EQE) of 3.97%. For the QD-LED based on ZTO, the device efficiency is improved by 1.7 times.

Suppressing Interface Strain for Eliminating Double-Slope Behaviors: Towards Ideal Conformable Polymer Field-Effect Transistors.

High-mobility polymer field-effect transistors (PFETs) are being actively explored for applications in soft electronic skin and low-cost flexible displays because of their superior solution processability, mechanical flexibility, and stretchability. However, most of high-mobility PFETs often deviate from the idealized behavior with variable mobility, large threshold voltage, and high off-state current, which masks their intrinsic properties and significantly impedes their practical applications. Here, it is first revealed that interface strain between polymer thin film and rigid substrate plays a crucial role in determining the ideality of PFETs, and demonstrate that various ideal conformable PFETs can be successfully fabricated by releasing strain. It is found that strain in film can be released by one-step peeling strategy, which can reduce π-π stacking distance and suppress generation of oxygen doped carriers, thereby obtaining linearly injected charge carriers and decreased carrier concentration in channel, eventually realizing ideal PFETs. More impressively, the fabricated ideal conformable PFET array displays outstanding conformability to curved objects, and meanwhile showing excellent organic light-emitting display driving capability. The work clarifies the effect of the interface strain on the device ideality, and strain can be effectively released by a facile peeling strategy, thus offering useful guidance for the construction of ideal conformable PFETs.

High-Mobility, Low-Voltage Programmable/Erasable Ferroelectric Polymer Transistor Nonvolatile Memory Based on a P(VDF-TrFE)/PMMA Bilayer Gate Insulator

Low mobility and high operating voltages are bottlenecks in the practical application of ferroelectric organic field-effect transistor (Fe-OFET) nonvolatile memory (NVM). In this article, we demonstrate a high-mobility polymer semiconductor-based Fe-OFET NVM that can well operate at low programming/erasing voltages ( V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</sub> /V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</sub> ). The issue that hinders the reduction of the V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</sub> /V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</sub> in Fe-OFET NVMs is discussed. We develop a route to resolve the issue by building a thin bilayer gate insulator consisted of an ultrathin poly(methyl methacrylate) (PMMA) and a thin poly(vinylidenefluoride-trifluoroethylene) films. The processing compatibility, that is, the tri-layered core architecture consisting of polymer semiconductor and insulator films is prepared by a full-solution technology, is confirmed. The mechanism of the performance improvements by using the ultrathin PMMA in the Fe-OFET NVMs is investigated. As a result, the Fe-OFET NVM exhibits excellent performances at low V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</sub> /V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</sub> of ±15 V, with a high mobility up to 1.75 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs, reliable memory endurance over 400 cycles, and stable memory retention over 65000 s.

High-Performance All-Polymer Solar Cells and Photodetectors Enabled by a High-Mobility n-Type Polymer and Optimized Bulk-Heterojunction Morphology

High-Performance All-Polymer Solar Cells and Photodetectors Enabled by a High-Mobility n-Type Polymer and Optimized Bulk-Heterojunction Morphology

Controlling Structural and Energetic Disorder in High-Mobility Polymer Semiconductors via Doping with Nitroaromatics

Molecular doping has emerged as a powerful strategy to tune the charge transport properties of organic field-effect transistors (OFETs). However, the limited tool-box of molecular dopants and unres...