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.     

氮杂苯并菲类n-型有机半导体材料研究进展

苯并菲盘状液晶是一类新型的有机电子学材料.该类材料多数以空穴传输功能为主,能传输电子的n-型材料较少.氮杂苯并菲是与苯并菲衍生物非常相似的一种杂环化合物,材料结构中引入了氮原子,吸电子能力得到增强,是潜在的n-型有机半导体材料,具有重要的应用价值.本文系统回顾了氮杂苯并菲类盘状液晶材料的研究进展,分类讨论了材料的分子结构,其中包括二、四、六氮杂苯并菲,以及它们的合成方法和物理化学性能,论述了材料在光电子领域的最新使用进展,并在此基础上,对该类液晶材料作为n-型有机半导体在光电子器件领域的应用前景进行了展望.     

Imide-Functionalized Polymer Semiconductors

Imide-functionalized π-conjugated polymer semiconductors have received a great deal of interest owing to their unique physicochemical properties and optoelectronic characteristics, including excellent solubility, highly planar backbones, widely tunable band gaps and energy levels of frontier molecular orbitals, and good film morphology. The organic electronics community has witnessed rapid expansion of the materials library and remarkable improvement in device performance recently. This review summarizes the development of imide-functionalized polymer semiconductors as well as their device performance in organic thin-film transistors and polymer solar cells, mainly achieved in the past three years. The materials mainly cover naphthalene diimide, perylene diimide, and bithiophene imide, and other imide-based polymer semiconductors are also discussed. The perspective offers our insights for developing new imide-functionalized building blocks and polymer semiconductors with optimized optoelectronic properties. We hope that this review will generate more research interest in the community to realize further improved device performance by developing new imide-functionalized polymer semiconductors.     

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.     

Solution-processable precursor route for fabricating ultrathin silica film for high performance and low voltage organic transistors

In this paper, we introduce a simple solution spin-coating method to fabricate silica thin film from precursor route in the condition of low temperature and atmospheric environment, which possesses a low leakage current, high capacitance, and low surface roughness. With silica film (~ 50 nm), high performance and low voltage (< 4 V) p-/n-type organic transistors are fabricated. This method shows great potential for industrialization owing to its characteristic of low consumption and energy saving, time-saving and easy to operate.     

基于蒽衍生高迁移率发光材料的研究进展

高迁移率发光有机半导体材料是实现有机发光场效应晶体管(OLETs)的重要材料, 但其设计合成面临巨大挑战. 本文综合评述了近年来高迁移率发光材料, 特别是基于蒽的高迁移率发光材料的研究进展, 重点介绍了目前报道的20余种基于蒽的高迁移率发光有机半导体材料, 包括分子的设计策略、 相关的光电性能及其在OLETs器件方面的应用研究, 以便为进一步的相关研究提供有意义的指导和借鉴. 本文还对该领域未来发展的挑战、 发展方向及机遇进行了简单评述.     

Quinoid-Aromatic Resonance for Very Small Optical Energy Gaps in Small-Molecule Organic Semiconductors: A Naphthodithiophenedione-oligothiophene Triad System

Organic semiconductors with very small optical energy gaps have attracted a lot of attention for near-infrared-active optoelectronic applications. Herein, we present a series of donor-acceptor-donor (D−A−D) organic semiconductors consisting of a highly electron-deficient naphtho[1,2-b:5,6-b′]dithiophene-2,7-dione quinoidal acceptor and oligothiophene donors that show very small optical energy gaps of down to 0.72 eV in the solid state. Investigation of the physicochemical properties of the D−A−D molecules as well as theoretical calculations of their electronic structures revealed an efficient intramolecular interaction between the quinoidal acceptor and the aromatic oligothiophene donors in the D−A−D molecules; this significantly enhances the backbone resonance and thus reduces the bond length alternation along the π-conjugated backbones. Despite the very small optical energy gaps, the D−A−D molecules have low-lying frontier orbital energy levels that give rise to air-stable ambipolar carrier transport properties with hole and electron mobilities of up to 0.026 and 0.043 cm² V⁻¹ s⁻¹, respectively, in field-effect transistors.     

Theoretically Rational Designs of Transport Organic Semiconductors Based on Heteroacenes

A Marcus electron transfer theory coupled with an incoherent polaron hopping and charge diffusion model in combining with first‐principle quantum chemistry calculation was applied to investigating the effects of heteroatom on the intermolecular charge transfer rate for a series of heteroacene molecules. The influences of intermolecular packing and charge reorganization energy were discussed. It was found that the sulphur and nitrogen substituted heteroacenes were intrinsically hole‐transporting materials due to the reduced hole reorganization energy and the enhanced overlap between HOMOs. For the oxygen‐substituted heteroacene, it was found that both the electronic couplings and the reorganization energies for holes and electrons were comparative, indicating the application potential of ambipolar devices. Most interestingly, for the boron‐substituted heteroacenes, theoretical calculations predicted a promising electron‐transport material, which is rare for organic materials. These findings provide insights into rationally designing organic semiconductors with specific properties.     

High and balanced hole and electron mobilities from ambipolar thin-film transistors based on nitrogen-containing oligoacences

We demonstrate a strategy for designing high-performance, ambipolar, acene-based field-effect transistor (FET) materials, which is based on the replacement of C-H moieties by nitrogen atoms in oligoacenes. By using this strategy, two organic semiconductors, 6,13-bis(triisopropylsilylethynyl)anthradipyridine (1) and 8,9,10,11-tetrafluoro-6,13-bis(triisopropylsilylethynyl)-1-azapentacene (3), were synthesized and their FET characteristics studied. Both materials exhibit high and balanced hole and electron mobilities, 1 having μ(h) and μ(e) of 0.11 and 0.15 cm(2)/V·s and 3 having μ(h) and μ(e) of 0.08 and 0.09 cm(2)/V·s, respectively. The successful demonstration of high and balanced ambipolar FET properties from nitrogen-containing oligoacenes opens up new opportunities for designing high-performance ambipolar organic semiconductors.     

Temperature Induced Aggregation of Organic Semiconductors

One important feature of organic semiconductors is their solution processability, which allows researchers to tune their aggregation states in solution and solid states and to control the processing conditions to reach desirable electronic and optoelectronic properties. Temperature is one of the most important processing parameters of organic semiconductors and has been studied extensively particularly for those conjugated small- and macro- molecules with strong temperature-dependent aggregation properties. This minireview summarizes the temperature-induced aggregation behaviors of organic semiconductors in solution, during solution casting and upon thermal annealing post-treatment of solid-state thin films. The influences of different aggregation states on the optoelectronic properties, in particular the photovoltaic properties, are discussed. The conclusions in this work will provide a rational guide to precisely control the aggregation states of organic semiconductors to fabricate high-performance optoelectronic devices.     

Organic Ambipolar Conjugated Molecules for Electronics: Synthesis and Structure–Property Relationships

The field of organic electronics has been developed vastly in the past two decades, and the performance and lifetime of these devices are critically dependent on the materials development, device design, deposition processes, and modeling, among which the active materials of organic semiconductor play a crucial role. The unique properties of organic semiconductor are largely based on the versatility to synthesize multifunctional organic conjugated materials by judicious molecular design. To effectively adjust the optoelectronic properties, especially energy levels, of organic semiconductor, the scientists have presented a synthesis methodology of organic ambipolar conjugated molecules, in which typical p‐dope type and n‐dope type segments are incorporated into one molecule. The present review summarizes the progress on organic ambipolar conjugated molecules for electronics in the past few years. Some issues to be addressed are also highlighted and discussed.

     

All-in-one: a new approach toward robust and solution-processable copper halide hybrid semiconductors by integrating covalent,coordinate and ionic bonds in their structures

Conventional inorganic semiconductors are best known for their superior physical properties and chemical robustness, and their widespread use in optoelectronic devices. However, implementation of these materials in many other applications has been hindered by their poor solubility and/or solution-processability, a longstanding drawback that is largely responsible for issues such as high cost. While recent progress on hybrid perovskites, an important class of inorganic–organic hybrid materials, has shed light on the development of high-performance solution processable semiconductors, they rely heavily on toxic metals and generally suffer from framework instability. To address these issues, a new group of hybrid semiconductors based on anionic copper(i) halide and cationic organic ligands has been developed. These compounds are noted as All-In-One (AIO) structures as they consist of covalently bonded anionic CuX inorganic modules that form both coordinate and ionic bonds with cationic organic ligands. Studies demonstrate that framework stability and solution processibility of these materials are greatly enhanced as a result of such bonds. In the perspective, we highlight the development of this newly emerged type of materials including their crystal structures, chemical and physical properties and possible applications. The untapped potential that the AIO approach can offer for other hybrid families is also discussed.

This Perspective features the newly emerged AIO-type Cu(i)X-based hybrid semiconductors and showcases their structural diversity, solution-processability, framework stability, important photophysical properties and related potential applications.     

High Electron Mobility Hot-Exciton Induced Delayed Fluorescent Organic Semiconductors

The development of high mobility emissive organic semiconductors is of great significance for the fabrication of miniaturized optoelectronic devices, such as organic light emitting transistors. However, great challenge exists in designing key materials, especially those who integrates triplet exciton utilization ability. Herein, dinaphthylanthracene diimides (DNADIs), with 2,6-extended anthracene donor, and 3′- or 4′-substituted naphthalene monoimide acceptors were designed and synthesized. By introducing acceptor-donor-acceptor structure, both materials show high electron mobility. Moreover, by fine-tuning of substitution sites, good integration with high solid state photoluminescence quantum yield of 26 %, high electron mobility of 0.02 cm² V⁻¹ s⁻¹, and the feature of hot-exciton induced delayed fluorescence were obtained in 4′-DNADI. This work opens a new avenue for developing high electron mobility emissive organic semiconductors with efficient utilization of triplet excitons.     

Ladder‐Type Heteroarene‐Based Organic Semiconductors

The fusion of heteroaromatic rings into ladder‐type heteroarenes can stabilize frontier molecular orbitals and lead to improved physicochemical properties that are beneficial for applications in various optoelectronic devices. Thus, ladder‐type heteroarenes, which feature highly planar backbones and well‐delocalized π conjugation, have recently emerged as a promising type of organic semiconductor with excellent device performance in organic photovoltaics (OPVs) and organic field‐effect transistors (OFETs). In this Focus Review, we summarize the recent advances in ladder‐type heteroarene‐based organic semiconductors, such as hole‐ and electron‐transporting molecular semiconductors, and fully ladder‐type conjugated polymers towards their applications in OPVs and OFETs. The recent use of ladder‐type small‐molecule acceptor materials has strikingly boosted the power conversion efficiency of fullerene‐free solar cells, and selected examples of the latest developments in ladder‐type fused‐ring electron acceptor materials are also elaborated.     

有机自旋光电子学的基本过程

有机自旋光电子学的研究方向分为磁场效应和自旋注入两个方面.研究表明,外加低磁场能够显著改变非磁性有机半导体材料的光致发光、注入电流、电致发光和光电流.这称为有机半导体材料的磁场效应.近年来,非磁性有机半导体材料的磁场效应引起了广泛的关注和研究兴趣.首先,有机半导体材料的磁场效应是强有力的实验手段,用以研究有机电学、光学和光电器件中电荷传输和激发态中的有用和无用过程,为解决电荷传输和激发态过程中的瓶颈问题提供有效的实验手段,为实现磁-光-电多功能集成提供科学原理,尤其是磁场效应能够为提高能量转换效率、探测和传感光电子学器件的响应频谱范围和灵敏度提供新思路.同时利用磁电极,有机半导体材料和器件中自旋注入及其对电荷传输和激发态过程的调控可以用于发展新型功能化的自旋光电子学器件.本文综述并讨论了有机半导体材料和器件中的磁场效应和自旋注入的光电子学效应.     

Unsymmetrically Chlorinated Non-Fused Electron Acceptor Leads to High-Efficiency and Stable Organic Solar Cells

Searching the cost-effective organic semiconductors is strongly needed in order to facilitate the practice of organic solar cells (OSCs), yet to be fulfilled. Herein, we have succeeded in developing two non-fused ring electron acceptors (NFREAs), leading to the highest efficiency of 16.2 % for the NFREA derived OSCs. These OSCs exhibit the superior operational stabilities under one sun equivalent illumination without ultraviolet (UV) filtration. It is revealed that the modulation of halogen substituents on aromatic side chains, as the new structural tool to tune the intermolecular interaction and optoelectronic properties of acceptors, not only promotes the interlocked tic-tac-toe frame of three-dimensional stacks in solid, but also improves charge dynamics of acceptors to enable high-performance and stable OSCs.     

有机光催化剂用于太阳能水分解：分子水平和聚集体水平改性

利用太阳能光解水产氢是实现氢能开发最绿色且可持续的理想技术。为了提高太阳能的转换效率，设计和发展高效、稳定、宽/全光谱响应光催化产氢体系成为关键研究课题。相比于无机半导体，有机半导体具有丰富的π电子和结构可修饰性，使其光学吸收和能带结构易剪裁，光催化路径多样。但低的介电常数造成其载流子迁移率低及迁移距离短。通过有目的地改变有机分子结构，可以轻松地设计和调控有机半导体的能带位置、增加摩尔吸光系数，改善材料对于整个太阳光谱中可见光或红外光的利用；通过功能分子微纳组装或集成，可进一步获得不同组分、维度(0维、1维、2维、3维)、尺寸、晶体学取向的有机光催化剂。有机微纳/复合结构的优异的比表面积、分子排布结构或能级排列结构可进一步提高太阳能的利用率和光生电荷的传输/分离效率，从而提高整体光电转换效率和产氢效率。然而，由于复杂的反应过程和设计困难，整个有机半导体的光催化物理化学过程仍不清楚。在这里，光催化的基本原理从光捕获、光激发电荷分离、表面反应的角度进行了讨论。随后详细总结了有机半导体纳米结构的制备方法包括超分子自组装、再沉淀法、气相沉积法以及其他方法。描述了典型的有机半导体材料，包括苝二酰...     

Controlling optical properties and electronic energy structure of I–III–VI semiconductor quantum dots for improving their photofunctions

I–III–VI multinary semiconductors, which have low toxicity, are attracting much attention as quantum dot (QD) materials for replacing conventional binary semiconductors that contain highly toxic heavy metals, Cd and Pb. Recently, the inherent design flexibility of multinary QDs has also been attracting attention, and optoelectronic property control has been demonstrated in many ways. Besides size control, the electronic and optical properties of multinary QDs can be changed by tuning the chemical composition with various methods including alloying with other semiconductors and deviation from stoichiometry. Due to significant progress in synthetic methods, the quality of such multinary QDs has been improved to a level similar to that of Cd-based binary QDs. Specifically, increased photoluminescence quantum yield and recently narrowed linewidth have led to new application fields for multinary QDs. In this review, a historical overview of the solution-phase synthesis of I–III–VI QDs is provided and the development of strategies for better control of optoelectronic properties, i.e., electronic structures, energy gap, optical absorption profiles, and photoluminescence feature, is discussed. In addition, applications of these QDs to luminescent devices and light energy conversion systems are described. The performance of prepared devices can be improved by controlling the optical properties and electronic structures of QDs by changing their size and composition. Clarification of the unique features of I–III–VI QDs in detail will be the base for further development of novel applications by utilizing the complexity of multinary QDs.     

Functional Organic Semiconductors Based on Bay‐Annulated Indigo (BAI)

The advancement of organic electronics has been continually pushed by the need for stable and high performance acceptor materials. By utilizing inexpensive and stable indigo dye as a starting material, Bay‐Annulated Indigo (BAI) provides a new motif for the development of semiconducting materials. Modular and straightforward synthesis makes BAI an outstanding platform for molecular design, while excellent stability, strong absorption, and high ambipolar mobility render BAI‐based materials excellent candidates for organic electronics. BAI‐based polymers and small molecules have taken advantage of these properties to show promising results in a variety of applications.     

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.