Solution-processed Polymer Research Articles

A Tricyclic Framework with Integrated B←N and Cyano Dual Functionalization for Superior n-Type Organic Electronics.

n-Type conjugated polymers featuring low-lying lowest unoccupied molecular orbital (LUMO) energy levels are essential for achieving high-performance n-type organic thin-film transistors (OTFTs) and organic thermoelectrics (OTEs). However, the synthesis of acceptors with strong electron-withdrawing characteristics presents a significant challenge. Herein, a peripheral functionalization strategy is employed on the tricyclic framework anthracene by introducing dual N,O-bidentate BF2/B(CN)2 groups to enhance its electron-withdrawing capability. This approach successfully navigates synthetic challenges, leading to the development of two novel acceptor building blocks: DBNF and DBNCN. Compared to the counterparts with a single N,O-bidentate BF2/B(CN)2 moiety, DBNF and DBNCN exhibit an extended π-backbone, enhanced molecular packing, and improved electron-withdrawing properties. Utilizing these innovative acceptor monomers, copolymers, PDBNF and PDBNCN, are synthesized, which exhibit considerably suppressed LUMO ≈-4.0 eV. The deep LUMO of PDBNF together with its favourable bimodal packing orientation leads to remarkable electron mobility of 3.04 cm2 V-1 s-1 with improved stability in OTFTs. Importantly, efficient n-doping in OTEs is achieved with PDBNCN, exhibiting exceptional conductivity of 95.5 S cm-1 and a maximum power factor of 147.8 μW m-1 K-2-among the highest reported for solution-processed n-type polymers. This work underscores the effectiveness of introducing dual B←N and cyano functionalities in attaining high-performance n-type plastic electronics.

Leaftronics: Natural lignocellulose scaffolds for sustainable electronics.

The global rise in electronic waste is alarming, driven by the persistent use of glass, epoxy, and plastic substrates owing to their cost, stability, flexibility, and transparency. This underscores the need for biodegradable alternatives with similar properties. This study shows that leaf-derived lignocellulose scaffolds can stabilize bio-sourced, solution-processed polymers by acting as natural sequestering media. Such reinforced films, even when based on gelatin (Tg ~ 60°C), can endure processes over 200°C. We demonstrate dip-coated ethyl cellulose films for commercially viable reflow soldered circuitry. The films offer high flexibility, more than 80% transparency, and surface roughness below 5.5 nm. Advanced OPDs and OECTs fabricated on these films perform comparably to those on glass and the low material cost and simple fabrication process yields a minimal carbon footprint of 1.6 kgCO2/m2. This work thus opens a vista of possibilities for biodegradable polymers heretofore considered unsuitable for making temperature-stable substrates for state-of-the-art electronics applications.

Accurate Determination of the Uniaxial Complex Refractive Index and the Optical Band Gap of Polymer Thin Films to Correlate Their Absorption Strength and Onset of Absorption.

The advanced development of optoelectronic devices requires a methodical knowledge of the fundamental material properties of the key active components. Systematic investigations and correlations of such basic optical properties can lead to new insights for the design of more potent materials. In this perspective, we provide a systematic overview of the uniaxial anisotropic complex refractive indices and the absorption coefficients obtained by ellipsometry as well as the optical band gap energies derived from Tauc plots of six selected solution-processed polymer thin films. While the optical band gap energies are intentionally distributed over the visible spectral range, we found that the absorption strength of all polymer samples are grouped in a random distribution within a rather uniform range of values.

Low-voltage operatable top-gated organic transistors based on the solution-processed binary polymers dielectric for simplifying the manufacturing flow of arrayed AMOLED

The complex process flow is an important factor that hinders the development of active-matrix organic light-emitting diode (AMOLED) displays. Organic thin-film transistors (OTFTs) are one of the promising candidates as the pixel circuits for AMOLEDs. Both the architecture and the fabrication of OTFTs are crucial elements to determine the process flow and cost of the AMOLEDs. In this Letter, we develop a strategy to significantly simplify the process flow and reduce the cost of AMOLEDs by constructing top-gated OTFTs with a solution-processed vertically phase separated binary polymer dielectric as the pixel circuits. The design on the OTFTs considers both the process flow and the device performance in terms of mobility and operating voltages. The mechanism to improve device performances is discussed. Finally, a 3 × 4 arrayed AMOLED is demonstrated, in which a high mobility over 0.3 cm2/Vs is obtained on the switching and driving OTFTs, and luminance over 300 cd/m2 is achieved on the OLEDs at the supplied low operating voltages of 10 V. This strategy provides a competitive technological route for the manufacturing of AMOLEDs.

Solution-Processed Polymer Memcapacitors with Stimulus-Controlled and Evolvable Synaptic Functionalities: From Short-Term Plasticity to Long-Term Plasticity to Metaplasticity.

In the vanguard of neuromorphic engineering, we develop a paradigm of biocompatible polymer memcapacitors using a seamless solution process, unleashing comprehensive synaptic capabilities depending on both the stimulation form and history. Like the human brain to learn and adapt, the memcapacitors exhibit analogue-type and evolvable capacitance shifts that mirror the complex flexibility of synaptic strengthening and weakening. With increasing frequency and intensity of the stimulation, the memcapacitors demonstrate an evolution from short-term plasticity (STP) to long-term plasticity (LTP), and even to metaplasticity (MP) at a higher level. A physical picture, featuring the stimulus-controlled spatiotemporal ion redistribution in the polymer, elaborates the origin of the memcapacitive prowess and resultant versatile synaptic plasticity. The distinctive MP behavior endows the memcapacitors with a dynamic learning rate (LR), which is utilized in an artificial neural network. The superiority of implementing a dynamic LR compared with conventional practices of using constant LR shines light on the potential of the memcapacitors to exploit organic neuromorphic computing hardware.

Free-Standing, Water-Resistant, and Conductivity-Enhanced PEDOT:PSS Films from In Situ Polymerization of 3-Hydroxymethyl-3-Methyl-Oxetane.

Free-standing films based on conducting polymers, such as poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS), offer many benefits over traditional metal electrodes for applications in flexible electronics. However, to ensure structural integrity when contacting aqueous environments and high levels of electrical conductivity, solution-processed polymers require additives that act as crosslinking agents and conductivity enhancers. In this work, a new approach is presented to fabricate water-resistant free-standing films of PEDOT:PSS and simultaneously increase their conductivity, using an oxetane compound as an additive. It is shown that at moderate temperatures, oxetane polymerizes within the PEDOT:PSS acidic medium, forming hydroxymethyl-substituted polyether compounds that form a network upon crosslinking with PSS. The polymer composite films show self-sustainability, structural stability in aqueous environments, and enhanced conductivity. Finally, the potential of the free-standing films as health-monitoring electrodes, specifically for human electrocardiography, is explored.

Improving interactions at the electrochromic polymer‐transparent oxide electrode interface using alkyl phosphonic acid modifiers

AbstractAs new synthetic methods for the preparation of solution processable electrochromic polymers are explored, including increasing synthetic scale beyond that of the research laboratory, it is expected that polymer intermolecular and intramolecular interactions will be affected. In this study, we explore the use of four different alkyl phosphonic acids of differing chain lengths as an interfacial treatment on ITO transparent electrodes to improve the polymer‐electrode interactions to mitigate the loss of film integrity and resulting electrochromic properties (current density, optical properties, and effective switch rates) during repeated oxidation/reduction and swelling/deswelling of the film. It was found that the phosphonic acid layer allows for a compatibilization of the polarity of the electrode surface with the polymer layer while also improving surface energy uniformity. We evaluated two electrochromic polymers (ECPs), and while a near complete delamination was observed on untreated ITO, film integrity was maintained beyond 25 repeated cycles, with polymer optical contrast maintained at all switching rates when coated onto dodecylphosphonic acid. Additionally, we show that electrochromic polymer film integrity is maintained over a range of film thicknesses. This method can be extended to applications using a variety of solution processable electroactive polymers in contact with metal oxide surfaces.

A High-Mobility n-Type Noncovalently-Fused-Ring Polymer for High-Performance Organic Thermoelectrics.

Conjugated polymers are emerging as competitive candidates for organic thermoelectrics (OTEs). However, to make the device truly pervasive, both p- and n-type conjugated polymers are essential. Despite great efforts, no n-type equivalents to the p-type benchmark PEDOT:PSS exist to date mainly due to the low electrical conductivity (σ). Herein, a near-amorphous n-type conjugated polymer, namely pDFSe, is reported with high σ by achieving the synergy between charge transport and doping efficiency. The polymer pDFSe is synthesized based on an acceptor-triad moiety of diketopyrrolopyrrole-difluorobenzoselenadiazole-diketopyrrolopyrrole (DFSe), which has the noncovalently-fused-ring structure to reinforce the backbone rigidity. Furthermore, an axisymmetric thiophene-selenophene-thiophene donor is introduced, which enables the formation of near-amorphous microstructures. The above merits ensure good doping efficiency without scarifying efficient intrachain charge-carrier transport. Thus, pDFSe-based n-type transistors exhibit high electron mobility up to 6.15 cm2 V-1 s-1, much higher than its reference polymer pDSe without the noncovalently-fused-ring structure (0.77 cm2 V-1 s-1). Further upon n-doping, pDFSe demonstrates excellent σ of 62.6 S cm-1 and maximum power factor of 133.1 μW m-1 K-2, which are among the highest values reported for solution-processed n-type polymers. The results demonstrate the great potential of near-amorphous n-type conjugated polymers with noncovalently-fused-ring structure for the next-generation OTEs.

PEDOT: PSS/PC71BM with various Rubrene doping levels for the production of Organic/Inorganic hybrid silicon solar cells with enhanced yield efficiency

Polymer-based solar cells (PSCs) have garnered considerable interest due to their potential advantages over traditional organic/inorganic hybrid silicon solar cells, including reduced material and production costs, compact substrates, and lightweight finished photovoltaic cells. To explore this further, we examined the impact of Rubrene in the PEDOT: PC71BM hole transport layer within the bulk Heterojunction framework of solution-processable polymer photovoltaic cells. Cells were created by combining PEDOT: PSS and PC71BM, incorporating Rubrene at 6, 9, 12, and 15 wt% ratios. The device structure comprised Si/PEDOT: PSS/PC71BM: Rubrene: DMSO/Ag, with Ag serving as a cathode fabricated in a low-pressure chamber. Notably, employing a 6 wt% Rubrene solution yielded improved short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), and power conversion efficiency (PCE) of 13.97 mA.cm−2, 514.80 mV, 40.97, and 2.948 %, respectively. These results demonstrate enhanced PCE with the addition of Rubrene compared to prior studies utilizing an active Rubrene surface.

Solution-processable polymers of intrinsic microporosity for selective silver removal from aqueous solution and subsequent disinfection by silver-laden coatings

Silver ions (Ag+) in waterways pose a growing threat to the environment and living organisms. Achieving an effective and green process for Ag+ removal requires an adsorbent with excellent specificity for silver ions and easy recoverability after fouling or blocking. However, this remains a major challenge. To address this concern, we developed a high-performance adsorbent by grafting polymers of intrinsic microporosity (PIM) with thioamide groups. This thioamide-modified PIM (TPIM-1) adsorbent exhibited an exceptional adsorption capacity of 656 mg g−1 and high selectivity (distribution coefficient of 833.3 mL g−1, selectivity coefficient of 346 over Cd2+) for aqueous Ag+ removal. TPIM-1 also features good solubility in selected solvents, allowing regeneration through a dissolution separation precipitation (DSP) procedure once fouling or blocking occurs. Over 80 % of the adsorption capacity was recovered after nine continuous regeneration cycles, showcasing potential cost-effective reusability. Density Functional Theory (DFT) results reveal that the grafted thioamide groups play a critical role in selective Ag+ adsorption, with a binding energy of 54 kcal mol−1. In addition, the Ag+-loaded PIM-coated glass surface showed excellent antibacterial ability, inhibiting the growth of Bacillus subtilis and E. coli. This study provides a viable strategy for the development of a low-carbon footprint silver removing adsorbent from wastewater.

Solution-Processed Ternary Perovskite-Conjugated Polymer Photodetector with a Photoresponse up to 1200 nm

Solution-Processed Ternary Perovskite-Conjugated Polymer Photodetector with a Photoresponse up to 1200 nm

Catalytic, Spectroscopic, and Theoretical Studies of Fe4S4-Based Coordination Polymers as Heterogenous Coupled Proton-Electron Transfer Mediators for Electrocatalysis.

Iron-sulfur clusters play essential roles in biological systems, and thus synthetic [Fe4S4] clusters have been an area of active research. Recent studies have demonstrated that soluble [Fe4S4] clusters can serve as net H atom transfer mediators, improving the activity and selectivity of a homogeneous Mn CO2 reduction catalyst. Here, we demonstrate that incorporating these [Fe4S4] clusters into a coordination polymer enables heterogeneous H atom transfer from an electrode surface to a Mn complex dissolved in solution. A previously reported solution-processable Fe4S4-based coordination polymer was successfully deposited on the surfaces of different electrodes. The coated electrodes serve as H atom transfer mediators to a soluble Mn CO2 reduction catalyst displaying good product selectivity for formic acid. Furthermore, these electrodes are recyclable with a minimal decrease in activity after multiple catalytic cycles. The heterogenization of the mediator also enables the characterization of solution-phase and electrode surface species separately. Surface enhanced infrared absorption spectroscopy (SEIRAS) reveals spectroscopic signatures for an in situ generated active Mn-H species, providing a more complete mechanistic picture for this system. The active species, reaction mechanism, and the protonation sites on the [Fe4S4] clusters were further confirmed by density functional theory calculations. The observed H atom transfer reactivity of these coordination polymer-coated electrodes motivates additional applications of this composite material in reductive H atom transfer electrocatalysis.

Fluorene-carbazole-based hyperbranched polymers with linear red TADF chromophores for high-efficiency white and red electroluminescent devices

Solution-processed polymer light emitting devices (PLEDs) using high-quality thermally activated delayed fluorescence (TADF) polymers as the emitting layers are attractive, however, high-efficiency white-light TADF polymers are very rare because of the complicated radiative transition channels. In this study, a series of hyperbranched TADF conjugated polymers were designed and synthesized which adopted the linear D-A-type TADF emitter of 1,8-naphthalimide-acridine as red chromophores, conjugated poly(fluorene-carbazole) as the blue backbone and triphenylamine as the hyperbranched cores. By adjusting the appropriate feed ratios of monomers, energy transfer process from the blue backbone to the red chromophores could be regulated and HR0.8 film had the highest photoluminescent quantum yield of 24%. Consequently, its doped electroluminescent device showed the cold-white emission with the CIE color coordinates of (0.35, 0.23) and the maximum EQE of 6.82%. By simply raising the concentration of the red chromophore in the polymers, the rapid reverse intersystem crossing (RISC) process and the enlarged energy gap between S1 and T1 were achievable.

Analysis of electrical and hysteresis characteristics of flexible OTFT using solution-processable DPP-DTT polymer and Parylene-C

Organic thin-film transistors (OTFTs) fabricated on Parylene-C substrates have the advantages of a simple process, low cost, and flexible characteristics. This study introduces the manufacturing method and electrical characteristics of an OTFT using organic materials as the substrate, gate dielectric, and channel material. PDPP2T-TT-OD(DPP-DTT) is used as the channel material, which is a highly mobile p-type polymer with good air stability. The proposed OTFT device has flexible characteristics because it is fabricated on a Parylene-C substrate and can be used even in a curved state. Furthermore, the manufacturing process was largely achieved via a simple, low-cost solution process using spin-coating and photolithography with a photo-curable material. Under flat conditions, the threshold voltage (VTH) is approximately –3 V, the average ION/IOFF ratio is approximately 105, and the mobility is 0.84 cm2/Vs.

Amidoxime-functionalized tetraphenylethylene ladder polymer for efficient membrane-based gas separations

Recent advances in solution-processible polymers of intrinsic microporosity (PIM) have attracted extensive research efforts in membrane-based gas separations due to their significantly enhanced gas permeability originating from inefficient chain packing. However, PIM-based membrane materials exhibit typically only moderate gas-pair selectivity, which is often insufficient especially for challenging gas separations containing highly sorbing feed components such as CO2. More importantly, they suffer from CO2-induced polymer chain dilation commonly referred as plasticization, which leads to poor separation performance under aggressive CO2/CH4 mixed-gas testing conditions. In this work, we conducted amidoxime (AO)-functionalization on a microporous tetraphenylethylene-based ladder polymer (TPE-PIM) by reacting its nitrile groups with hydroxyl amine under reflux conditions. Because of strong inter-chain hydrogen bonding, AO-functionalized TPE polymer (AO-TPE) exhibited a tightened and rigidified microstructure with 64 % reduction in Brunauer-Emmett-Teller (BET) surface area (175 m2/g) as compared to TPE-PIM (485 m2/g) derived from N2 adsorption isotherms at 77 K. As a result, fresh AO-TPE showed decreased gas permeability concurrent with a two-fold increase in CO2/CH4 selectivity (from 18 to 40) compared to TPE-PIM. Under aggressive 50:50 CO2:CH4 mixed-gas testing conditions, AO-TPE showed a strong plasticization resistance with decreased CH4 permeability over total feed pressure ranging from 4 to 30 bar. At 20 bar total pressure, AO-TPE demonstrated a mixed-gas CO2/CH4 selectivity of 37.7 as compared to 14.5 for TPE-PIM. The simple AO functionalization strategy holds promise to be an effective post-modification method to increase gas selectivity and alleviate the detrimental effects from CO2-induced plasticization.

Room temperature synthesis, characterization and enhanced gas transport properties of novel poly(oxindolylidene arylene)s with dibenzothiophene, dibenzothiophene-S-oxide and dibenzothiophene-S,S-dioxide fragments in the main chain

Aromatic sulfur-containing polymers poly(arylene ether sulfone)s and poly(arylene sulfide sulfone)s are widely used in membrane-based gas- and liquid separations and purification technologies. In this work, we report a facile, robust, room temperature synthesis of a series of novel, solution processable aromatic polymers containing dibenzothiophene, dibenzothiophene-S-oxide, and dibenzothiophene-S,S-dioxide fragments in the main chain, alternating with bulky, torsion resistant oxindolylidene groups. The NMR studies of the polymers obtained revealed ladderized, rigid kink-structured backbones. This combination provides membranes with higher permeability and selectivity with gas pairs CO2/CH4, H2/CH4 and H2/N2, close to or even surpassing the 2008 Robeson’s trade-off line, that compare favorably with polysulfones and poly(ether sulfone)s reported in the literature that lie below the 1991 upper bond. Polymer P2-SO2 containing dibenzothiophene-S,S-dioxide fragments showed impressive CO2 and H2 permeabilities (243. 3 and 315.1 Barrer, respectively); on the other hand, P1-SO containing dibenzothiophene-S-oxide exhibited remarkable H2/CH4 and H2/N2 selectivity (127.26 and 99.34, respectively). This work offers a novel and facile route to fabricate various polysulfones and polysulfoxides with reversible-tunable gas separation properties inspired by the concept of rigid kink-structured backbones that shift their gas transport properties towards higher permeability and higher selectivity.

Solution-processed high-k photopatternable polymers for low-voltage electronics.

High dielectric constant (k) polymers have been widely explored for flexible, low-power-consumption electronic devices. In this work, solution-processable high-k polymers were designed and synthesized by ultraviolet (UV) triggered crosslinking at a low temperature (60 °C). The highly crosslinked network allows for high resistance to organic solvents and high breakdown strength over 2 MV cm-1. The UV-crosslinking capability of the polymers enables them to achieve a high-resolution pattern with a feature size down to 1 μm. Further investigation suggests that the polar cyano pendants in side chains are responsible for increasing the dielectric constant up to 10 in a large-area device array, thereby contributing to a low driving voltage of 5 V and high field-effect mobility exceeding 20 cm2 V-1 s-1 in indium gallium zinc oxide (IGZO) thin-film transistors (TFTs). In addition, the solution-processable high-k dielectric polymers were utilized to fabricate flexible low-voltage organic TFTs, which show highly reliable and reproducible mechanical stability at a bending radius of 5 mm after 1000 cycles. And also, the high radiation stability of the dielectric polymers was observed in a UV-sensitive TFT device, thereby achieving highly reproducible pattern recognition, which is promising for artificial optic nerve circuits.

Viologen-based solution-processable ionic porous polymers for electrochromic applications.

Electrochromic porous thin films are promising for applications in smart windows and energy-efficient optical displays. However, their generally poor processing ability and excessive processing times remain grand challenges. Herein, we report the design and convenient synthesis of core-altered N-arylated viologens with aldehyde groups (πV-CHO) as new building blocks to prepare soluble, viologen-embedded ionic porous polymers. We also demonstrate that these polymers can be easily solution-processed by drop-coating to fabricate high-quality electrochromic films with tunable optoelectronic properties in a cost-effective fashion. The prepared films exhibit excellent electrochromic performance, including a low driving voltage (1.2-1.4 V), fast switching times (0.8-1.7 s), great coloration efficiency (73-268 cm2 C-1), remarkably high optical contrast up to 95.6%, long cycling stability, and tunable oxidation and reduction colors. This work sheds important light on a new molecular engineering approach to produce redox-active polymers with combined properties of intrinsic porosity, reversible and tunable redox activity, and solution processability. This provides the materials with an inherently broad utility in a variety of electrochemical devices for energy storage, sensors, and electronic applications.

Efficient solution-processed narrowband green-emitting organic light emitting diodes sensitized by a thermally activated delayed fluorescence polymer

Solution-processed TADF polymer sensitized MR-TADF OLEDs demonstrate EQE of 15.7% with a narrow FWHM of 48 nm.

Triptycene-like naphthopleiadene as a readily accessible scaffold for supramolecular and materials chemistry.

Triptycene derivatives are used extensively in supramolecular and materials chemistry, however, most are prepared using a multi-step synthesis involving the generation of a benzyne intermediate, which hinders production on a large scale. Inspired by the ease of the synthesis of resorcinarenes, we report the rapid and efficient preparation of triptycene-like 1,6,2',7'-tetrahydroxynaphthopleiadene directly from 2,7-dihydroxynaphthalene and phthalaldehyde. Structural characterisation confirms the novel bridged bicyclic framework, within which the planes of the single benzene ring and two naphthalene units are fixed at an angle of ∼120° relative to each other. Other combinations of aromatic 1,2-dialdehydes and 2,7-disubstituted naphthalenes also provided similar triptycene-like products. The low cost of the precursors and undemanding reaction conditions allow for rapid multigram synthesis of 1,6,2',7'-tetrahydroxynaphthopleiadene, which is shown to be a useful precursor for making the parent naphthopleiadene hydrocarbon. The great potential for the use of the naphthopleiadene scaffold in supramolecular and polymer chemistry is demonstrated by the preparation of a rigid novel cavitand, a microporous network polymer, and a solution-processable polymer of intrinsic microporosity.