An n-Type Polythiophene Derivative with Excellent Thermoelectric Performance

Typical n-type conjugated polymers are based on fused-ring electron-accepting building blocks. Herein, we report a non-fused-ring strategy to design n-type conjugated polymers, i.e. introducing electron-withdrawing imide or cyano groups to each thiophene unit of a non-fused-ring polythiophene backbone. The resulting polymer, n-PT1 , shows low LUMO/HOMO energy levels of −3.91 eV/−6.22 eV, high electron mobility of 0.39 cm² V⁻¹ s⁻¹ and high crystallinity in thin film. After n-doping, n-PT1 exhibits excellent thermoelectric performance with an electrical conductivity of 61.2 S cm⁻¹ and a power factor (PF) of 141.7 μW m⁻¹ K⁻². This PF is the highest value reported so far for n-type conjugated polymers and this is the first time for polythiophene derivatives to be used in n-type organic thermoelectrics. The excellent thermoelectric performance of n-PT1 is due to its superior tolerance to doping. This work indicates that polythiophene derivatives without fused rings are low-cost and high-performance n-type conjugated polymers.     

A High-Performance n-Type Thermoelectric Polymer from C−H/C−H Oxidative Direct Arylation Polycondensation

n-Type conjugated polymers (CPs) are crucial in the applications of organic electronics. Direct coupling of electron-deficient C−H monomer via selective C−H activation, namely C−H/C−H oxidative direct arylation polycondensation (Oxi-DArP), is an ideal approach toward such CPs. Herein, Oxi-DArP is firstly adopted to synthesize a high-performance n-type CP using a newly developed monomer, i.e., 3,6-di(thiazol-5-yl)-diketopyrrolopyrrole (Tz-5-DPP). Tz-5-DPP based homopolymer PTz - 5 - DPP with a molecular weight of 22 kDa has been synthesized via Oxi-DArP. After n-doping, PTz - 5 - DPP films exhibited electric conductivity values up to 8 S cm⁻¹ and power factors (PFs) up to 106 μW m⁻¹ K⁻². Notably, this PF value is the highest for n-type polymer thermoelectric materials to date. The Oxi-DArP synthesis and the excellent n-type performance of the polymer make this work an important step toward the straightforward and sustainable preparation of high-performance n-type polymer semiconductors.     

Chlorine-Substituted N-Heteroacene Analogues Acting as Organic Semiconductors for Solution-Processed n-type Organic Field-Effect Transistors

High performance solution processable n-type organic semiconductor is an essential element to realize low-cost, all organic and flexible composite logic circuits. In the design of n-type semiconducting materials, tuning the LUMO level of compounds is a key point. As a strong electron withdrawing unit, the introduction of chlorine atom into the chemical structure can increase the electron affinity of the material and reduce the LUMO energy level. Here, a series chlorine substituted N-heteroacene analogues of 6,7,8,9-tetrachloro-4,11-bis(4-((2-ethylhexyl)oxy)phenyl)-[1,2,5]thiadiazolo[3,4-b]phenazine (O4Cl), 6,7,8,9-tetrachloro-4,11-bis(4-((2-ethylhexyl)thio)phenyl)-[1,2,5]thiadiazolo[3,4-b]phenazine (S4Cl), 1,2,3,4,8,9,10,11-octachloro-6,13-bis(4-((2-ethylhexyl)oxy)phenyl)quinoxalino[2,3-b]phenazine (8Cl) and 12Cl have been synthesized and characterized. Solution-processed organic field-effect transistors (OFETs) based on these four compounds exhibit good electron mobilities of 0.04 cm² V⁻¹ s⁻¹, 0.01 cm² V⁻¹ s⁻¹, 2×10⁻³ cm² V⁻¹ s⁻¹ and 3×10⁻³ cm² V⁻¹ s⁻¹, respectively, under ambient conditions. The results suggest that these chlorine substituted π-conjugated N-heteroacene analogues are promising n-type semiconductors in OFET applications.     

Side-Chain Molecular Engineering of Triazole-Based Donor-Acceptor Polymeric Photocatalysts with Strong Electron Push-Pull Interactions

A new series of donor-acceptor (D-A)-type semiconductive polymers were generated by the integration of electron-deficient alkyl chain anchored triazole (TA) moieties and electron-rich pyrene units into the polymer skeleton. The polymer series demonstrated satisfactory light-harvesting ability and suitable band gaps. In the series, polymer P-TAME benefits from a minimized exciton binding energy, strongest D-A interaction, and favorable hydrophilicity, affording an outstanding photocatalytic H₂ evolution rate of ca. 100 μmol h⁻¹ (10 mg polymer, AQY_{420 nm}=8.9 %) and H₂O₂ production rate of ca. 190 μmol h⁻¹ (20 mg polymer) under visible-light irradiation, which is superior to most currently reported polymers. All polymers in the series can mediate water oxidation reactions to evolve O₂. Thus, these TA-based polymers open up a new avenue toward tailor-made efficient photocatalysts with broad photocatalytic activities.     

Promising hole-transporting materials for perovskite solar cells: Modulation of the electron-deficient units in triphenylamine derivative-based molecules

Modulation of the electron-deficient π-bridge units in 4-methoxy-N-(4-methoxyphenyl)-N-phenylbenzenamine (MeTPA)-based hole-transporting materials (HTMs) is a significant approach to improve hole mobility of HTMs for perovskite solar cells (PSCs). In this study, a class of simple MeTPA-based HTMs (H1-H4) with different π-bridged electron-deficient units were designed for the purpose of providing a theoretical model to obtain potential MeTPA-based HTMs. The results indicated that H2 to H4 exhibit better performance, such as larger Stokes shifts, smaller exciton-binding energy, better stability, good solubility, and higher hole mobility, in comparison with the parental material H1. H2 to H4 materials with high hole mobility (5.45 × 10⁻⁴, 2.70 × 10⁻¹, and 3.99 × 10⁻³ cm² V⁻¹ second⁻¹, respectively) may embody promising HTMs to yield good performance in PSCs. Therefore, the useful information obtained regarding control of the electron-deficient π-bridge units of MeTPA-based HTMs is an effective way to obtain excellent HTMs for PSC applications.     

Synthesis and Optoelectronic Applications of dπ–pπ Conjugated Polymers with a Di-metallaaromatic Acceptor

The development of conjugated polymers especially n-type polymer semiconductors is powered by the design and synthesis of electron-deficient building blocks. Herein, a strong acceptor building block with di-metallaaromatic structure was designed and synthesized by connecting two electron-deficient metallaaromatic units through a π-conjugated bridge. Then, a double-monomer polymerization methodology was developed for inserting it into conjugated polymer scaffolds to yield metallopolymers. The isolated well-defined model oligomers indicated polymer structures. Kinetic studies based on nuclear magnetic resonance and ultraviolet–visible spectroscopies shed light on the polymerization process. Interestingly, the resulted metallopolymers with d_π–p_π conjugations are very promising electron transport layer materials which can boost photovoltaic performance of an organic solar cell, with power conversion efficiency up to 18.28 % based on the PM6 : EH-HD-4F non-fullerene system. This work not only provides a facile route to construct metallaaromatic conjugated polymers with various functional groups, but also discovers their potential applications for the first time.     

Functionalized Phenanthrene Imide-Based Polymers for n-Type Organic Thin-Film Transistors

High-performing n-type polymers are crucial for the advance of organic electronics field, however strong electron-deficient building blocks with optimized physicochemical properties for constructing them are still limited. The imide-functionalized polycyclic aromatic hydrocarbons ( PAH s) with extended π-conjugated framework, high electron deficiency and good solubility serve as promising candidates for developing high-performance n-type polymers. Among the PAH s, phenanthrene ( PhA ) features a well-delocalized aromatic π-system with multiple modifiable active sites . However, the PhA -based imides are seldom studied, mainly attributed to the synthetic challenge. Herein, we report two functionalized PhA s, CPOI and CPCNI , by simultaneously incorporating imide with carbonyl or dicyanomethylene onto PhA . Notably, the dicyanomethylene-modified CPCNI exhibits a well stabilized LUMO energy level (−3.84 eV), attributed to the synergetic inductive effect from imide and cyano groups. Subsequently, based on CPOI and CPCNI , two polymers PCPOI-Tz and PCPCNI-Tz were developed. Applied to organic thin-film transistors, owing to the strong electron-deficiency of CPCNI , polymer PCPCNI-Tz shows an improved electron mobility and largely decreased threshold voltage compared with PCPOI-Tz . This work affords two structurally novel electron-deficient building blocks and highlights the effectiveness of dual functionalization of PhA s with strong electron-withdrawing groups for devising n-type polymers.     

Well-Balanced Ambipolar Charge Transport of Diketopyrrolepyrrole-Based Copolymers: Organic Field-Effect Transistors and High-Voltage Logic Applications

A poly (3,6-bis(thiophen-2-yl)−2,5-bis(2-decyltetradecyl)−2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione-co-(2,3-bis(phenyl)acrylonitrile)) (PDPADPP) copolymer, composed of diketopyrrolopyrrole (DPP) and a cyano (nitrile) group with a vinylene spacer linking two benzene rings, is synthesized via a palladium-catalyzed Suzuki coupling reaction. The electrical performance of PDPADPP in organic field-effect transistors (OFETs) and circuits is investigated. The OFETs based on PDPADPP exhibit typical ambipolar transport characteristics, with the as-cast OFETs demonstrating low field-effect hole and electron mobility values of 0.016 and 0.004 cm² V⁻¹ s⁻¹, respectively. However, after thermal annealing at 240 °C, the OFETs exhibit improved transport characteristics with highly balanced ambipolar transport, showing average hole and electron mobility values of 0.065 and 0.116 cm² V⁻¹ s⁻¹, respectively. To verify the application of the PDPADPP OFETs in high-voltage logic circuits, compact modeling using the industry-standard small-signal Berkeley short-channel IGFET model (BSIM) is performed, and the logic application characteristics are evaluated. The circuit simulation results demonstrate excellent logic application performance of the PDPADPP-based ambipolar transistor and illustrate that the device annealed at 240 °C exhibits ideal circuit characteristics.     

Isomeric anthracene diimide polymers

N-type semiconducting polymers are attractive for organic electronics, but desirable electron-deficient units for synthesizing such polymers are still lacking. As a cousin of rylene diimides such as naphthalene diimide (NDI) and perylene diimide (PDI), anthracene diimide (ADI) is a promising candidate; its polymers, however, have not been achieved yet because of synthetic challenges for its polymerizable monomers. Herein, we present ingenious synthesis of two dibromide ADI monomers with dibromination at differently symmetrical positions of the ADI core, which are further employed to construct ADI polymers. More interestingly, the two obtained ADI polymers possess the same main-chain and alkyl-chain structures but different backbone conformations owing to varied linking positions between repeating units. This feature enables their different optoelectronic properties and film-state packing behavior. The ADI polymers offer first examples of conjugated polymer conformational isomers and are highly promising as a new class of n-type semiconductors for various organic electronics applications.

Two anthracene diimide (ADI) polymers with the backbone conformational isomerism, new members of aromatic diimide polymers family, have been synthesized as a class of highly promising n-type semiconductors for organic electronics.     

A Dual-Ligand Porous Coordination Polymer Chemiresistor with Modulated Conductivity and Porosity

Single-ligand-based electronically conductive porous coordination polymers/metal–organic frameworks (EC-PCPs/MOFs) fail to meet the requirements of numerous electronic applications owing to their limited tunability in terms of both conductivity and topology. In this study, a new 2D π-conjugated EC-MOF containing copper units with mixed trigonal ligands was developed: Cu₃(HHTP)(THQ) (HHTP=2,3,6,7,10,11-hexahydrotriphenylene, THQ=tetrahydroxy-1,4-quinone). The modulated conductivity (σ≈2.53×10⁻⁵ S cm⁻¹ with an activation energy of 0.30 eV) and high porosity (ca. 441.2 m² g⁻¹) of the Cu₃(HHTP)(THQ) semiconductive nanowires provided an appropriate resistance baseline and highly accessible areas for the development of an excellent chemiresistive gas sensor.     

Distannylated Bithiophene Imide: Enabling High-Performance n-Type Polymer Semiconductors with an Acceptor–Acceptor Backbone

A distannylated electron-deficient bithiophene imide (BTI-Tin) monomer was synthesized and polymerized with imide-functionalized co-units to afford homopolymer PBTI and copolymer P(BTI-BTI2), both featuring an acceptor–acceptor backbone with high molecular weight. Both polymers exhibited excellent unipolar n-type character in transistors with electron mobility up to 2.60 cm² V⁻¹ s⁻¹. When applied as acceptor materials in all-polymer solar cells, PBTI and P(BTI-BTI2) achieved high power-conversion efficiency (PCE) of 6.67 % and 8.61 %, respectively. The PCE (6.67 %) of polymer PBTI, synthesized from the distannylated monomer, is much higher than that (0.14 %) of the same polymer PBTI*, synthesized from typical dibrominated monomer. The 8.61 % PCE of copolymer P(BTI-BTI2) is also higher than those (<1 %) of homopolymers synthesized from dibrominated monomers. The results demonstrate the success of BTI-Tin for accessing n-type polymers with greatly improved device performance.     

Electron-Deficient Polycyclic Molecules via Ring Fusion for n-Type Organic Electrochemical Transistors

The primary challenge for n-type small-molecule organic electrochemical transistors (OECTs) is to improve their electron mobilities and thus the key figure of merit μC*. Nevertheless, few reports in OECTs have specially proposed to address this issue. Herein, we report a 10-ring-fused polycyclic π-system consisting of the core of naphthalene bis-isatin dimer and the terminal moieties of rhodanine, which features intramolecular noncovalent interactions, high π-delocalization and strong electron-deficient characteristics. We find that this extended π-conjugated system using the ring fusion strategy displays improved electron mobilities up to 0.043 cm² V⁻¹ s⁻¹ compared to our previously reported small molecule gNR, and thereby leads to a remarkable μC* of 10.3 F cm⁻¹ V⁻¹ s⁻¹ in n-type OECTs, which is the highest value reported to date for small-molecule OECTs. This work highlights the importance of π-conjugation extension in polycyclic-fused molecules for enhancing the performance of n-type small-molecule OECTs.     

An Amorphous n-Type Conjugated Polymer with an Ultra-Rigid Planar Backbone

High charge carrier mobility polymer semiconductors are always semi-crystalline. Amorphous conjugated polymers represent another kind of polymer semiconductors with different charge transporting mechanism. Here we report the first near-amorphous n-type conjugated polymer with decent electron mobility, which features a remarkably rigid, straight and planar polymer backbone. The molecular design strategy is to copolymerize two fused-ring building blocks which are both electron-accepting, centrosymmetrical and planar. The polymer is the alternating copolymer of double B←N bridged bipyridine (BNBP) unit and benzobisthiazole (BBTz) unit. It shows a decent electron mobility of 0.34 cm² V⁻¹ s⁻¹ in organic field-effect transistors. The excellent electron transporting property of the polymer is possibly due to the ultrahigh backbone stiffness, small π-π stacking distance, and high molecular weight.     

Recent structural evolution of lactam- and imide-functionalized polymers applied in organic field-effect transistors and organic solar cells

Organic semiconductor materials, especially donor–acceptor (D–A) polymers, have been increasingly applied in organic optoelectronic devices, such as organic field-effect transistors (OFETs) and organic solar cells (OSCs). Plenty of high-performance OFETs and OSCs have been achieved based on varieties of structurally modified D–A polymers. As the basic building block of D–A polymers, acceptor moieties have drawn much attention. Among the numerous types, lactam- and imide-functionalized electron-deficient building blocks have been widely investigated. In this review, the structural evolution of lactam- or imide-containing acceptors (for instance, diketopyrrolopyrrole, isoindigo, naphthalene diimide, and perylene diimide) is covered and their representative polymers applied in OFETs and OSCs are also discussed, with a focus on the effect of varied structurally modified acceptor moieties on the physicochemical and photoelectrical properties of polymers. Additionally, this review discusses the current issues that need to be settled down and the further development of new types of acceptors. It is hoped that this review could help design new electron-deficient building blocks, find a more valid method to modify already reported acceptor units, and achieve high-performance semiconductor materials eventually.

This review highlights the recent structural evolution of lactam- and imide-functionalized polymers applied in organic field-effect transistors and organic solar cells.     

Two-Dimensional Conjugated Polymer Synthesized by Interfacial Suzuki Reaction: Towards Electronic Device Applications

Preparing two-dimensional conjugated polymers (2DCPs) with desirable structures and semiconducting properties is promising but remains a great challenge. Presented here is a new 2DCP, named 2D polytriethyltriindole (2DPTTI), which is efficiently synthesized by a modified interfacial Suzuki reaction from 2,7,12-tribromo-5,10,15-triethyltriindole (2-BrTTI) and 1,4-benzenediboronic acid dipinacol ester (BADE) precursors at room temperature. Wafer-scale free-standing 2DPTTI films with controllable thicknesses between 2.5 and 46.0 nm were obtained by adjusting the experimental conditions. The resulting 2DPTTI films, used as an active layer in organic field effect transistors (OFETs), exhibited typical p-type semiconducting properties and superior UV optoelectronic performance with a photosensitivity of 3.7×10³ and responsivity of 1.4×10³ A W⁻¹, as well as a light-blue fluorescence character. This report provides a general approach for constructing various semiconducting 2DCPs, by an interfacial Suzuki reaction, towards multifunctional organic electronics.     

新型共轭聚合物的设计合成及其在场效应晶体管的应用

近年来,有机场效应晶体管(OFETs)由于在柔性器件和可穿戴电子学中的潜在应用受到了学术界和工业界的普遍关注,尤其是以聚合物半导体材料构筑的晶体管性能得到了快速的发展.如何设计合成用于OFETs的高性能聚合物半导体材料,一直是我们的追求目标.然而,分子结构对迁移率的影响仍缺少系统的比较.本文综述了近年来国内外新型聚合物材料的最新进展.我们按照材料的种类以及载流子的传输类型进行了分类,对高性能聚合物材料的发展过程、材料的设计思路以及相应的FETs性能进行了系统地归纳总结.通过研究分子及分子聚集态结构与器件性能之间的关系,希望为以后设计合成新型的高性能的聚合物材料提供有益的借鉴和指导.     

Solution-Processable Unsymmetrical Triarylamines: Towards High Mobility and ON/OFF Ratio in Bottom-Gated OFETs

Self-assembly of organic small molecules into an ordered thin film has been the key strategy towards efficient charge transport for organic field-effect transistors (OFETs). Solution processing is a feasible and economic way to enhance pi–pi interaction. Herein, nitrile-substituted unsymmetrical triarylamines for OFET applications with high mobility are reported. The compounds were constructed by Suzuki cross-coupling reactions under inert conditions. The HOMO level of about 5.3 eV indicates good hole-transporting ability. OFETs were assembled in bottom-gate, top-contact architecture. Devices fabricated from a binary solvent system exhibited excellent p-channel characteristics, with impressively high charge-carrier mobility of up to 2.58 cm² V⁻¹ s⁻¹ and I_ON/OFF current ratios of 10⁶–10⁷. SEM and AFM analysis showed the efficient molecular self-assembly attained by the simple and effective solvent-engineering method. Theoretical insights obtained by DFT calculations supported by single-crystal structures showed that the crystalline nature and packing modes of these compounds ensure high mobility. The results prove that these compounds have great potential for use in numerous electronic applications, such as sensors and logic switches.     

An In-Situ Cyanidation Strategy To Access Tetracyanodiacenaphthoanthracene Diimides with High Electron Mobilities Exceeding 10 cm2 V−1 s−1

A family of novel highly π-extended tetracyano-substituted acene diimides, named as tetracyanodiacenaphthoanthracene diimides (TCDADIs), have been synthesized using a facile four-fold Knoevenagel condensation strategy. Unlike conventional cyano substitution reactions, our approach enables access to a large π-conjugated backbone with the in-situ formation of four cyano substitutents at room temperature while avoiding extra cyano-functionalization reactions. TCDADIs decorated with different N-alkyl substituents present good solubility, near-coplanar backbones, good crystallinity, and low-lying lowest unoccupied molecular orbital energies of −4.33 eV, all of which contribute to desirable electron-transport performance when applied in organic field-effect transistors (OFET). The highest electron mobility of an OFET based on a 2-hexyldecyl-substituted TCDADI single crystal reaches 12.6 cm² V⁻¹ s⁻¹, which is not only among the highest values for the reported n-type organic semiconductor materials (OSMs) but also exceeds that of most n-type OSMs decorated with imide units.     

Novel highly soluble 3,3′-bicarbazolyl based polymers for optoelectronics

Novel family of highly soluble polymers containing 3.3′-bicarbazolyl moieties is reported. Utilizing simple and efficient chemical oxidation of carbazole and its derivatives by iron trichloride exclusively and quantitatively yields the bicarbazolyl dimmers with reactive oxirane groups. The polymers were prepared in polyaddition reaction of bicarbazolyl-containing diepoxydes with 4,4′-thiobisbenzenethiol, 2,5-dimercapto-1,3,4-thiadiazole, or 1,3-benzenedithiol in the presence of catalyst triethylamine. Obtained compounds were characterized using GPC, DSC, IR, UV, fluorescence and ¹H NMR spectroscopy. The hole drift mobility reaches 10⁻⁴ cm²/Vs at high electric fields. Such processable polymers with conjugated-nonconjugated repeating units in the main chain and good charge carrier mobility are quite promising for fabrication of optoelectronic devices.