High-performance N-type Polymer Research Articles

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 (PAHs) with extended π-conjugated framework, high electron deficiency and good solubility serve as promising candidates for developing high-performance n-type polymers. Among the PAHs, 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 PhAs, 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 PhAs with strong electron-withdrawing groups for devising n-type polymers.

Cyano-Functionalized Pyrazine: A Structurally Simple and Easily Accessible Electron-Deficient Building Block for n-Type Organic Thermoelectric Polymers.

Developing low-cost and high-performance n-type polymer semiconductors is essential to accelerate the application of organic thermoelectrics (OTEs). To achieve this objective, it is critical to design strong electron-deficient building blocks with simple structure and easy synthesis, which are essential for the development of n-type polymer semiconductors. Herein, we synthesized two cyano-functionalized highly electron-deficient building blocks, namely 3,6-dibromopyrazine-2-carbonitrile (CNPz) and 3,6-Dibromopyrazine-2,5-dicarbonitrile (DCNPz), which feature simple structures and facile synthesis. CNPz and DCNPz can be obtained via only one-step reaction and three-step reactions from cheap raw materials, respectively. Based on CNPz and DCNPz, two acceptor-acceptor (A-A) polymers, P(DPP-CNPz) and P(DPP-DCNPz) are successfully developed, featuring deep-positioned lowest unoccupied molecular orbital (LUMO) energy levels, which are beneficial to n-type organic thin-film transistors (OTFTs) and OTEs performance. An optimal unipolar electron mobility of 0.85 and 1.85 cm2 V-1 s-1 is obtained for P(DPP-CNPz) and P(DPP-DCNPz), respectively. When doped with N-DMBI, P(DPP-CNPz) and P(DPP-DCNPz) show high n-type electrical conductivities/power factors of 25.3 S cm-1 /41.4 μW m-1 K-2 , and 33.9 S cm-1 /30.4 μW m-1 K-2 , respectively. Hence, the cyano-functionalized pyrazine CNPz and DCNPz represent a new class of structurally simple, low-cost and readily accessible electron-deficient building block for constructing n-type polymer semiconductors.

High-Performance n-type Polymer Field-effect Transistors with Exceptional Stability

Development of organic field-effect transistors (OFETs) that simultaneously exhibit high-performance and high-stability is critical for complementary integrated circuits and other applications based on organic semiconductors. While progress has been made...

High-Performance n-Type Polymeric Mixed Ionic-Electronic Conductors: The Impacts of Halogen Functionalization.

Developing high-performance n-type polymer mixed ionic-electronic conductors (PMIECs) is a grand challenge, which largely determines their applications in vaious organic electronic devices, such as organic electrochemical transistors (OECTs) and organic thermoelectrics (OTEs). Herein, two halogen-functionalized PMIECs f-BTI2g-TVTF and f-BTI2g-TVTCl built from fused bithiophene imide dimer (f-BTI2) as the acceptor unit and halogenated thienylene-vinylene-thienylene (TVT) as the donor co-unit are reported. Compared to the control polymer f-BTI2g-TVT, the fluorinated f-BTI2g-TVTF shows lower-positioned lowest unoccupied molecular orbital (LUMO), improved charge transport property, and greater ion uptake capacity. Consequently, f-BTI2g-TVTF delivers a state-of-the-artµC* of 90.2 F cm-1 V-1 s-1 with a remarkable electron mobility of 0.41 cm2 V-1 s-1 in OECTs and an excellent power factor of 64.2 µW m-1 K-2 in OTEs. An OECT-based inverter amplifier is further demonstrated with voltage gain up to 148V V-1 , which is among the highest values for OECT inverters. Such results shed light on the impacts of halogen atoms on developing high-performing n-type PMIECs.

A Rational Design of Isoindigo-Based Conjugated Microporous n-Type Semiconductors for High Electron Mobility and Conductivity.

The development of n-type organic semiconductors has evolved significantly slower in comparison to that of p-type organic semiconductors mainly due to the lack of electron-deficient building blocks with stability and processability. However, to realize a variety of organic optoelectronic devices, high-performance n-type polymer semiconductors are essential. Herein, conjugated microporous polymers (CMPs) comprising isoindigo acceptor units linked to benzene or pyrene donor units (BI and PI) showing n-type semiconducting behavior are reported. In addition, considering the challenges of deposition of a continuous and homogeneous thin film of CMPs for accurate Hall measurements, a plasma-assisted fabrication technique is developed to yield uniform thin films. The fully conjugated 2D networks in PI- and BI-CMP films display high electron mobility of 6.6 and 3.5cm2 V-1 s-1 , respectively. The higher carrier concentration in PI results in high conductivity (5.3mScm-1 ). Both experimental and computational studies are adequately combined to investigate structure-property relations for this intriguing class of materials in the context of organic electronics.

Cyano-Functionalized Fused Bithiophene Imide Dimer-Based n-Type polymers for High-Performance Organic Thermoelectrics.

Doped n-type polymers usually exhibit low electrical conductivities and thermoelectric power factors (PFs), restricting the development of high-performance p-n junction-based organic thermoelectrics (OTEs). Herein we report the design and synthesis of a new cyano-functionalized fused bithiophene imide dimer (f-BTI2), CNI2, which synergistically combines the advantages of both cyano and imide functionalities, thus leading to substantially higher electron deficiency than the parent f-BTI2. On the basis of this novel building block, a series of n-type donor-acceptor and acceptor-acceptor polymers were successfully synthesized, all of which show good solubility, deep-lying frontier molecular orbital levels, and favorable polymer chain orientation. Among them, the acceptor-acceptor polymer PCNI2-BTI delivers an excellent electrcial conductivity up to 150.2 S cm-1 and a highest PF of 110.3 μW m-1 K-2 in n-type OTEs, attributed to the optimized polymer electronic properties and film morphology with improved molecular packing and higher crystallinity assisted by solution-shearing technology. The PF value is the record of n-type polymers for OTEs to date. This work demonstrates a facile approach to designing high-performance n-type polymers and fabricating high-quality films for OTE applications. This article is protected by copyright. All rights reserved.

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.

N-Type Polymer Semiconductors Based on Dithienylpyrazinediimide.

The development of n-type organic semiconductors critically relies on the design and synthesis of highly electron-deficient building blocks with good solubility and small steric hindrance. We report here a strongly electron-deficient dithienylpyrazinediimide (TPDI) and its n-type semiconducting polymers. The pyrazine substitution leads to the resulting polymers with much lower-lying lowest unoccupied molecular orbital (LUMO) levels and improved backbone planarity compared to the reported dithienylbenzodiimide (TBDI)- and fluorinated dithienylbenzodiimide (TFBDI)-based polymer analogues, thus yielding n-type transport character with an electron mobility up to 0.44 cm2 V-1 s-1 in organic thin-film transistors. These results demonstrate that dithienylpyrazinediimide is a highly promising electron-deficient building block for constructing high-performance n-type polymers and the incorporation of pyrazine into imide-functionalized (hetero)arenes is an effective strategy to develop n-type polymers with deep-lying frontier molecular orbital (FMO) levels for organic optoelectronic devices.

Imide-Functionalized Fluorenone and Its Cyanated Derivative Based n-Type Polymers: Synthesis, Structure-Property Correlations, and Thin-Film Transistor Performance.

The development of high-performance n-type polymer semiconductors is powered by the design and synthesis of electron-deficient building blocks with optimized physicochemical properties. By meticulously installing an imide group onto fluorene and its cyanated derivative, we report here two very electron-deficient building blocks, imide-functionalized fluorenone (FOI) and its cyanated derivative (FCNI), both featuring a deep-lying lowest unoccupied molecular orbital energy level down to -4.05 eV and highly coplanar framework, endowing them ideal units for constructing n-type polymers. Thus, a series of polymers are built from them, exhibiting unipolar n-type transport character with a highest electron mobility of 0.11 cm2 V-1 s-1 . Hence, FOI and FCNI offer a remarkable platform for accessing high-performance n-type polymers and the imide functionalization of appropriate (hetero)arenes is a powerful strategy for developing polymers with deep-lying LUMOs for n-type organic electronics.

Fused Bithiophene Imide Dimer-Based n-Type Polymers for High-Performance Organic Electrochemical Transistors.

The development of n-type organic electrochemical transistors (OECTs) lags far behind their p-type counterparts. In order to address this dilemma, we report here two new fused bithiophene imide dimer (f-BTI2)-based n-type polymers with a branched methyl end-capped glycol side chain, which exhibit good solubility, low-lying LUMO energy levels, favorable polymer chain orientation, and efficient ion transport property, thus yielding a remarkable OECT electron mobility (μe ) of up to ≈10-2 cm2 V-1 s-1 and volumetric capacitance (C*) as high as 443 F cm-3 , simultaneously. As a result, the f-BTI2TEG-FT-based OECTs deliver a record-high maximum geometry-normalized transconductance of 4.60 S cm-1 and a maximum μC* product of 15.2 F cm-1 V-1 s-1 . The μC* figure of merit is more than one order of magnitude higher than that of the state-of-the-art n-type OECTs. The emergence of f-BTI2TEG-FT brings a new paradigm for developing high-performance n-type polymers for low-power OECT applications.

Acceptor–acceptor-type conjugated polymer semiconductors

Series of acceptor–acceptor-type conjugated polymer semiconductors have been developed and applied to the electron transport of OFETs and PSCs. This study summarized their advances in polymerization methods, molecular structures and device applications. The rapid development of electronic devices such as organic field-effect transistors (OFETs) and solar cells makes the research and development of electronic transport materials imminent. The acceptor–acceptor-type (A−A-type) conjugated n-type polymer semiconductors have caught much attention due to the outstanding advantages on excellent electron-accepting capabilities, the precise adjustment of energy levels and the mass production at low fabrication cost. This article systematically reviews the polymerization methods of A−A-type polymers and the recent advancements applied in OFETs and polymer solar cells (PSCs). The analyses of the synthesis and the relationship between device performances and polymer molecular structures may provide a constructive guidance for the further development of high-performance n-type polymer materials.

High-Performance All-Polymer Solar Cells Enabled by n-Type Polymers with an Ultranarrow Bandgap Down to 1.28 eV.

Compared to organic solar cells based on narrow-bandgap nonfullerene small-molecule acceptors, the performance of all-polymer solar cells (all-PSCs) lags much behind due to the lack of high-performance n-type polymers, which should have low-aligned frontier molecular orbital levels and narrow bandgap with broad and intense absorption extended to the near-infrared region. Herein, two novel polymer acceptors, DCNBT-TPC and DCNBT-TPIC, are synthesized with ultranarrow bandgaps (ultra-NBG) of 1.38 and 1.28 eV, respectively. When applied in transistors, both polymers show efficient charge transport with a highest electron mobility of 1.72 cm2 V-1 s-1 obtained for DCNBT-TPC. Blended with a polymer donor, PBDTTT-E-T, the resultant all-PSCs based on DCNBT-TPC and DCNBT-TPIC achieve remarkable power conversion efficiencies (PCEs) of 9.26% and 10.22% with short-circuit currents up to 19.44 and 22.52 mA cm-2 , respectively. This is the first example that a PCE of over 10% can be achieved using ultra-NBG polymer acceptors with a photoresponse reaching 950 nm in all-PSCs. These results demonstrate that ultra-NBG polymer acceptors, in line with nonfullerene small-molecule acceptors, are also available as a highly promising class of electron acceptors for maximizing device performance in all-PSCs.

A Conjugated Polymer Containing a B ← N Unit for Unipolar n-Type Organic Field-Effect Transistors

Solution-processed organic field-effect transistors (OFETs) have great potential for next-generation “plastic electronics”. The development of n-type polymer semiconductors still lags far behind that of p-type polymer semiconductors, including material number and device performance. Moreover, the reported high-performance n-type polymer semiconductors are mostly based on amide and imide units. To enrich the family of n-type polymers and promote the development of OFETs, we have proposed using a boron–nitrogen coordination bond (B←N) to develop n-type polymer semiconductors. In this work, we report a B←N-containing conjugated polymer, PBN-13, which is an alternating polymer of a double B←N-bridged bipyridine unit and a 5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole unit. This polymer exhibits strong aggregation ability in solution and good crystallinity in a thin film, which are very desirable for achieving good electron-transporting properties. The OFET device based on PBN-13 shows unipolar ...

Cyano-Substituted Head-to-Head Polythiophenes: Enabling High-Performance n-Type Organic Thin-Film Transistors.

Polythiophenes, built on the electron-rich thiophene unit, typically possess high-lying energy levels of the lowest unoccupied molecular orbitals (LUMOs) and show hole-transporting properties. In this study, we develop a series of n-type polythiophenes, P1-P3, based on head-to-head-linked 3,3'-dialkoxy-4,4'-dicyano-2,2'-bithiophene (BTCNOR) with distinct side chains. The BTCNOR unit shows not only highly planar backbone conformation enabled by the intramolecular noncovalent sulfur-oxygen interaction but also significantly suppressed LUMO level attributed to the cyano-substitution. Hence, all BTCNOR-based polymer semiconductors exhibit low-lying LUMO levels, which are ∼1.0 eV lower than that of regioregular poly(3-hexylthiophene) (rr-P3HT), a benchmark p-type polymer semiconductor. Consequently, all of the three polymers can enable unipolar n-type transport characteristics in organic thin-film transistors (OTFTs) with low off-currents ( Ioffs) of 10-10-10-11 A and large current on/off ratios ( Ion/ Ioffs) at the level of 106. Among them, polymer P2 with a 2-ethylhexyl side chain offers the highest film ordering, leading to the best device performance with an excellent electron mobility (μe) of 0.31 cm2 V-1 s-1 in off-center spin-cast OTFTs. To the best of our knowledge, this is the first report of n-type polythiophenes with electron mobility comparable to the hole mobility of the benchmark p-type rr-P3HT and approaching the electron mobility of the most-studied n-type polymer, poly(naphthalene diimide- alt-bithiophene) (i.e., N2200). The change of charge carrier polarity from p-type (rr-P3HT) to n-type (P2) with comparable mobility demonstrates the obvious effectiveness of our structural modification. Adoption of n-hexadecyl (P1) and 2-butyloctyl (P3) side chains leads to reduced film ordering and results in 1-2 orders of magnitude lower μes, showing the critical role of side chains in optimizing device performance. This study demonstrates the unique structural features of head-to-head linkage containing BTCNOR for constructing high-performance n-type polymers, i.e., the alkoxy chain for backbone conformation locking and providing polymer solubility as well as the strong electron-withdrawing cyano group for lowering LUMO levels and enabling n-type performance. The design strategy of BTCNOR-based polymers provides useful guidelines for developing n-type polythiophenes.

Wafer-Scale Fabrication of High-Performance n-Type Polymer Monolayer Transistors Using a Multi-Level Self-Assembly Strategy.

Wafer-scale fabrication of high-performance uniform organic electronic materials is of great challenge and has rarely been realized before. Previous large-scale fabrication methods always lead to different layer thickness and thereby poor film and device uniformity. Herein, the first demonstration of 4 in. wafer-scale, uniform, and high-performance n-type polymer monolayer films is reported, enabled by controlling the multi-level self-assembly process of conjugated polymers in solution. Since the self-assembly process happened in solution, the uniform 2D polymer monolayers can be facilely deposited on various substrates, and theoretically without size limitations. Polymer monolayer transistors exhibit high electron mobilities of up to 1.88 cm2 V-1 s-1 , which is among the highest in n-type monolayer organic transistors. This method allows to easily fabricate n-type conjugated polymers with wafer-scale, high uniformity, low contact resistance, and excellent transistor performance (better than the traditional spin-coating method). This work provides an effective strategy to prepare large-scale and uniform 2D polymer monolayers, which could enable the application of conjugated polymers for wafer-scale sophisticated electronics.

Air-Stable n-Type Polymers for Thermoelectric Applications

Polymer-based thermoelectrics have the potential for waste heat recovery and energy harvesting from temperatures less than 200°C. These devices can be fabricated via printing processes that are low cost from materials that are lightweight and flexible, with applications ranging from self-powered sensors to wearable electronics. In the past decade, significant progress has been made with high performing p-type thermoelectrics such as PEDOT-derivatives, while n-type polymers have lagged behind due to their air sensitivity and low electrical conductivity. In this work, we optimize the thermoelectric properties of metallo-organic polymers with nickel as the metal center. We report the synthesis, characterization and thermoelectric properties of poly(nickel-ethenetetrathiolate) and poly(nickel-tetrathiooxalate) that are intrinsically electrically conducting. We modify the extent of oxidation and study the role of different oxidants and counterions on tuning the electrical conductivity. Interestingly, the Seebeck coefficient (thermopower) remains largely unchanged over the course of oxidation indicating that this may be a viable technique to decouple thermopower and electrical conductivity in such materials. The temperature dependent properties for these polymers show semi-conducting behavior that is consistent with hopping transport. Film measurements by blending with an inert matrix indicate that these polymers maintain their stability in air, making them suitable for energy harvesting devices. To enhance the Seebeck coefficient, we blend the metallo-organic polymers with other materials to form composites. This enables optimization of the power factor to realize high performance n-type polymer thermoelectrics.

Nitrile-substituted thienyl and phenyl units as building blocks for high performance n-type polymer semiconductors

Conjugated polymers containing nitrile-substituted thienyl and phenyl units displayed high electron mobility under ambient conditions.

“Conformation Locked” Strong Electron-Deficient Poly(p-Phenylene Vinylene) Derivatives for Ambient-Stable n-Type Field-Effect Transistors: Synthesis, Properties, and Effects of Fluorine Substitution Position

The charge carrier mobility of p-type and ambipolar polymer field-effect transistors (FETs) has been improved substantially. Nonetheless, high-mobility n-type polymers are rare, and few can be operated under ambient conditions. This situation is mainly caused by the scarcity of strong electron-deficient building blocks. Herein, we present two novel electron-deficient building blocks, FBDOPV-1 and FBDOPV-2, with low LUMO levels down to -4.38 eV. On the basis of both building blocks, we develop two poly(p-phenylene vinylene) derivatives (PPVs), FBDPPV-1 and FBDPPV-2, for high-performance n-type polymer FETs. The introduction of the fluorine atoms effectively lowers the LUMO levels of both polymers, leading to LUMO levels as low as -4.30 eV. Fluorination endows both polymers with not only lower LUMO levels, but also more ordered thin-film packing, smaller π-π stacking distance, stronger interchain interaction and locked conformation of polymer backbones. All these factors provide FBDPPV-1 with high electron mobilities up to 1.70 cm(2) V(-1) s(-1) and good stability under ambient conditions. Furthermore, when polymers have different fluorination positions, their backbone conformations in solid state differ, eventually leading to different device performance.