Electron transporting semiconducting polymers in organic electronics

Significant progress has been achieved in the preparation of semiconducting polymers over the past two decades, and successful commercial devices based on them are slowly beginning to enter the market. However, most of the conjugated polymers are hole transporting, or p-type, semiconductors that have seen a dramatic rise in performance over the last decade. Much less attention has been devoted to electron transporting, or n-type, materials that have lagged behind their p-type counterparts. Organic electron transporting materials are essential for the fabrication of organic p-n junctions, organic photovoltaic cells (OPVs), n-channel organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs) and complementary logic circuits. In this critical review we focus upon recent developments in several classes of electron transporting semiconducting polymers used in OLEDs, OFETs and OPVs, and survey and analyze what is currently known concerning electron transporting semiconductor architecture, electronic structure, and device performance relationships (87 references).     

高性能双极性聚合物半导体材料与晶体管器件

有机聚合物半导体材料与晶体管器件是融合了化学、材料、半导体以及微电子等学科的前沿交叉研究方向.聚合物半导体材料分子是该领域研究的重要内容,其中双极性聚合物分子半导体材料,兼具了电子和空穴的双重载流子输运能力而受到学术界的广泛关注.本文总结了双极性聚合物半导体材料与器件的研究进展,重点介绍了我们在D-A型双极性聚合物分子半导体材料设计、加工技术与器件制备以及功能应用方面的研究工作,并论述了双极性聚合物分子半导体材料与器件研究过程中存在的科学问题及发展方向.     

Unravelling the Superiority of Nonbenzenoid Acepleiadylene as a Building Block for Organic Semiconducting Materials**

Acepleiadylene (APD), a nonbenzenoid isomer of pyrene, exhibits a unique charge-separated character with a large molecular dipole and a small optical gap. However, APD has never been explored in optoelectronic materials to take advantage of these appealing properties. Here, we employ APD as a building block in organic semiconducting materials for the first time, and unravel the superiority of nonbenzenoid APD in electronic applications. We have synthesized an APD derivative (APD-IID) with APD as the terminal donor moieties and isoindigo (IID) as the acceptor core. Theoretical and experimental investigations reveal that APD-IID has an obvious charge-separated structure and enhanced intermolecular interactions as compared with its pyrene-based isomers. As a result, APD-IID displays significantly higher hole mobilities than those of the pyrene-based counterparts. These results imply the advantages of employing APD in semiconducting materials and great potential of nonbenzenoid polycyclic arenes for optoelectronic applications.     

Angular-shaped naphthalene tetracarboxylic diimides for n-channel organic transistor semiconductors

A series of compounds based on the angular-shaped naphthalene tetracarboxylic diimide core have been synthesized, characterized and used as active layers of organic field-effect transistors (OFETs). The fabricated OFET devices exhibit n-type semiconducting characteristics, demonstrating the first examples of semiconductors based on angular-shaped naphthalene tetracarboxylic diimides.     

并五苯及其衍生物在有机场效应晶体管中的应用

有机场效应晶体管（organic field—effect transistors,OFETs）是以有机半导体材料作为有源层,通过电场控制电流的电子器件．与传统的无机半导体器件相比,由于其可应用于生产大面积、柔性、低成本电子设备而备受关注,在有机存储器件、有机太阳能电池、柔性平板显示和电子纸等众多领域具有潜在而广泛的应用前景．并苯类材料因其紧密的分子堆积及优异的半导体性能被广泛研究．其中,并五苯及其衍生物在场效应晶体管中表现出良好的性质,其效果甚至可以与非晶硅相媲美,但并五苯较差的溶解性及环境稳定性阻碍了其进一步应用．科研工作者通过对分子结构进行修饰改造设计,合成了一系列并五苯的衍生物,其不仅在稳定性、电学性能和溶解性方面有很大提高,还可以将该p-型半导体材料拓展到双极性及n-型半导体材料领域．本文对并五苯及其衍生物在有机场效应晶体管中的应用进行了较为全面的综述,期望对该领域的研究起到一定的推动作用．     

High-performance and multifunctional organic field-effect transistors

Organic field-effect transistors(OFETs) refer to field-effect transistors that use organic semiconductors as channel materials. Owing to the advantages of organic materials such as solution processability and intrinsic flexibility, OFETs are expected to be applicable in emergent technologies including wearable electronics and sensors, flexible displays, internet-of-things, neuromorphic computing, etc. Improving the electrical performance and developing multifunctionalities of OFETs are two major...     

Tailoring crystal polymorphs of organic semiconductors towards high-performance field-effect transistors

As a quite ubiquitous phenomenon, crystal polymorph is one of the key issues in the field of organic semiconductors. This review gives a brief summary to the advances on polymorph control of thin film and single crystal of representative organic semiconductors towards high-performance field-effect transistors. Particularly, the relationship between crystal polymporh and charge transport behaviour has been discussed to shed light on the rational preparation of outstanding organic semiconducting materials with desired crystal polymorph.     

Rational design of diarylethylene-based polymeric semiconductors for high-performance organic field-effect transistors

Constructing planar, rigid, and high electronically delocalized π-conjugated molecular system is the most basic requirements of obtaining high-performance polymeric semiconductors for organic field-effect transistors (OFETs). In this regard, diarylethylene (DAE)-based polymers show great potential because many substantive progresses related to polymer field-effect transistors had been achieved from the kind of polymer materials in recent years. In the brief review, series of DAE-based polymer are highlighted, based on which several design strategies have been summarized by the way of comparative research method. These strategies have important guiding significance not only for further developing new DAE-based and other polymeric semiconductors for OFETs but also for developing specific polymeric semiconductors for other organic electronics, such as organic photovoltaics and organic light-emitting diodes. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 585–603     

Progresses in organic field-effect transistors and molecular electronics

In the past years, organic semiconductors have been extensively investigated as electronic materials for organic field-effect transistors (OFETs). In this review, we briefly summarize the current status of organic field-effect transistors including materials design, device physics, molecular electronics and the applications of carbon nanotubes in molecular electronics. Future prospects and investigations required to improve the OFET performance are also involved. __________ Translated from Huaxue Tongbao (Chemistry), 2006, 69(6) (in Chinese)     

A highly pi-stacked organic semiconductor for field-effect transistors based on linearly condensed pentathienoacene

We present the synthesis and characterization of a fused-ring compound, dithieno[2,3-d:2',3'-d']thieno[3,2-b:4,5-b']dithiophene (pentathienoacene, PTA). In contrast to pentacene, PTA has a larger band gap than most semiconductors used in organic field-effect transistors (OFETs) and therefore is expected to be stable in air. The large pi-conjugated and planar molecular structure of PTA would also form higher molecular orders that are conductive for carrier transport. X-ray diffraction and atomic force microscopy experiments on its films show that the molecules stack in layers with their long axis upright from the surface. X-ray photoelectron spectroscopy suggests that there are no chemical bonds at the PTA/Au interface. OFETs based on the PTA have been constructed, and their performances as p-type semiconductors are also presented. A high mobility of 0.045 cm(2)/V s and an on/off ratio of 10(3) for a PTA OFET have been achieved, demonstrating the potential of PTA for application in future organic electronics.     

Noncovalent conformational locks in organic semiconductors

Highly planar conformation is considered to be one of the most important properties for high performance organic semiconductors. Among all kinds strategies for designing highly performing materials, noncovalent conformational locks(NCLs)have been widely used to increase the planarity and rigidity for π-conjugated systems. This review summarizes π-conjugated small molecules and polymers by employing various NCLs for controlling molecular conformation in the past two years. The optoelectronic properties of the conjugated materials, together with their applications on organic field-effect transistors(OFETs)and organic photovoltaics(OPVs) are discussed. Besides, the outlook and challenges in this field are also presented. It is obvious that NCLs play an important role in the design and synthesis of high-performance organic semiconductors.     

High-performance organic field-effect transistors: molecular design, device fabrication, and physical properties

In the past decade, tremendous progress has been made in organic field-effect transistors (OFETs). Their real applications require further development of device performance. OFETs consist of organic semiconductors, dielectric layers, and electrodes. Organic semiconductors play a key role in determining the device characteristics. The properties of the organic semiconductors, such as molecular structure and packing, as well as molecular energy levels, can be properly controlled by molecular design. Therefore, we designed and synthesized a series of organic molecules. The synthesized organic semiconductors exhibit excellent field-effect properties due to strong intermolecular interactions and proper molecular energy levels. Meanwhile, the influence of the device fabrication process, organic semiconductor/dielectric layer interface, and organic layer/electrode contact on the device performance was investigated. A deep understanding of these factors is helpful to improve field-effect properties. Furthermore, single-crystal field-effect transistors are highlighted because the single-crystal-based FETs can provide an accurate conducting mechanism of organic semiconductors and higher device performance as compared with thin film FETs.     

HOMO Stabilisation in π‐Extended Dibenzotetrathiafulvalene Derivatives for Their Application in Organic Field‐Effect Transistors

Three new organic semiconductors, in which either two methoxy units are directly linked to a dibenzotetrathiafulvalene (DB‐TTF) central core and a 2,1,3‐chalcogendiazole is fused on the one side, or four methoxy groups are linked to the DB‐TTF, have been synthesised as active materials for organic field‐effect transistors (OFETs). Their electrochemical behaviour, electronic absorption and fluorescence emission as well as photoinduced intramolecular charge transfer were studied. The electron‐withdrawing 2,1,3‐chalcogendiazole unit significantly affects the electronic properties of these semiconductors, lowering both the HOMO and LUMO energy levels and hence increasing the stability of the semiconducting material. The solution‐processed single‐crystal transistors exhibit high performance with a hole mobility up to 0.04 cm² V^?1 s^?1 as well as good ambient stability.     

Functionalization of Pyrene To Prepare Luminescent Materials—Typical Examples of Synthetic Methodology

Pyrene‐based π‐conjugated materials are considered to be an ideal organic electro‐luminescence material for application in semiconductor devices, such as organic light‐emitting diodes (OLEDs), organic field‐effect transistors (OFETs) and organic photovoltaics (OPVs), and so forth. However, the great drawback of employing pyrene as an organic luminescence material is the formation of excimer emission, which quenches the efficiency at high concentration or in the solid‐state. Thus, in order to obtain highly efficient optical devices, scientists have devoted much effort to tuning the structure of pyrene derivatives in order to realize exploitable properties by employing two strategies, 1) introducing a variety of moieties at the pyrene core, and 2) exploring effective and convenient synthetic strategies to functionalize the pyrene core. Over the past decades, our group has mainly focused on synthetic methodologies for functionalization of the pyrene core; we have found that formylation/acetylation or bromination of pyrene can selectly lead to functionalization at K‐region by Lewis acid catalysis. Herein, this Minireview highlights the direct synthetic approaches (such as formylation, bromination, oxidation, and de‐tert‐butylation reactions, etc.) to functionalize the pyrene in order to advance research on luminescent materials for organic electronic applications. Further, this article demonstrates that the future direction of pyrene chemistry is asymmetric functionalization of pyrene for organic semiconductor applications and highlights some of the classical asymmetric pyrenes, as well as the latest breakthroughs. In addition, the photophysical properties of pyrene‐based molecules are briefly reviewed. To give a current overview of the development of pyrene chemistry, the review selectively covers some of the latest reports and concepts from the period covering late 2011 to the present day.     

Modelling charge transport in organic semiconductors: from quantum dynamics to soft matter

The charge carrier dynamics in organic semiconductors has been traditionally discussed with the models used in inorganic crystalline and amorphous solids but this analogy has severe limitations because of the more complicated role of nuclear motions in organic materials. In this perspective, we discuss how a new approach to the modelling of charge transport is emerging from the alliance between the conventional quantum chemical methods and the methods more traditionally used in soft-matter modelling. After describing the conventional limit cases of charge transport we discuss the problems arising from the comparison of the theory with the experimental and computational results. Several recent applications of numerical methods based on the propagation of the wavefunction or kinetic Monte Carlo methods on soft semiconducting materials are reviewed.     

Recent Advances in Isoindigo‐Inspired Organic Semiconductors

Over the past decade, isoindigo has become a widely used electron‐deficient subunit in donor‐acceptor organic semiconductors, and these isoindigo‐based materials have been widely used in both organic photovoltaic (OPV) devices and organic field effect transistors (OFETs). Shortly after the development of isoindigo‐based semiconductors, researchers began to modify the isoindigo structure in order to change the optoelectronic properties of the resulting materials. This led to the development of many new isoindigo‐inspired compounds; since 2012, the Kelly Research Group has synthesized a number of these isoindigo analogues and produced a variety of new donor‐acceptor semiconductors. In this Personal Account, recent progress in the field is reviewed. We describe how the field has evolved from relatively simple donor‐acceptor small molecules to structurally complex, highly planarized polymer systems. The relevance of these materials in OPV and OFET applications is highlighted, with particular emphasis on structure‐property relationships.     

Benzodicarbomethoxytetrathiafulvalene derivatives as soluble organic semiconductors

A series of new tetrathiafulvalene (TTF) derivatives bearing dimethoxycarbonyl and phenyl or phthalimidyl groups fused to the TTF core (6 and 15-18) has been synthesized as potential soluble semiconductor materials for organic field-effect transistors (OFETs). The electron-withdrawing substituents lower the energy of the HOMO and LUMO levels and increase the solubility and stability of the semiconducting material. Crystal structures of all new TTF derivatives are also described, and theoretical DFT calculations were carried out to study the potential of the crystals to be used in OFET. In the experimental study, the best performing device exhibited a hole mobility up to 7.5 × 10(-3) cm(2) V(-1) s(-1)).     

Organic semiconductors for solution-processable field-effect transistors (OFETs)

The cost-effective production of flexible electronic components will profit considerably from the development of solution-processable, organic semiconductor materials. Particular attention is focused on soluble semiconductors for organic field-effect transistors (OFETs). The hitherto differentiation between "small molecules" and polymeric materials no longer plays a role, rather more the ability to process materials from solution to homogeneous semiconducting films with optimal electronic properties (high charge-carrier mobility, low threshold voltage, high on/off ratio) is pivotal. Key classes of materials for this purpose are soluble oligoacenes, soluble oligo- and polythiophenes and their respective copolymers, and oligo- and polytriarylamines. In this context, micro- or nanocrystalline materials have the general advantage of somewhat higher charge-carrier mobilities, which, however, could be offset in the case of amorphous, glassy materials by simpler and more reproducible processing.     

Monolayer organic field-effect transistors

Monolayer organic field-effect transistors(OFETs) are attracting worldwide interest in device physics and novel applications due to their ultrathin active layer for two-dimensional charge transport. The monolayer films are generally prepared by thermal evaporation, the Langmuir technique or self-assembly process, etc., but their electrical performance is relatively lower than corresponding thick films. From 2011, the performance of monolayer OFETs has been boosted by using the monolayer molecular crystals(MMCs) as active channels, which opened up a new era for monolayer OFETs. In this review, recent progress of monolayer OFETs, including the preparation of monolayer films, their OFET performance and applications are summarized.Finally, perspectives of monolayer OFETs in the near future are also discussed.