Highly emissive white single-molecular material towards organic light-emitting transistors

Organic light-emitting transistors(OLETs)are miniaturized electroluminescent devices,and they simultaneously integrate the dual functionality of switching in organicfield-effect transistors and emission in organic light-emitting diodes,which have recently aroused interest from scientists for the next-generation of display applications[1–3].Notably,white organic light-emitting transistors(WOLETs)have gained much attention for their potential applications in sensors,switches,and light sources,including indoor lighting,street lighting andflood lighting[4].Moreover,the Commission Internationale de l’Elcairage(CIE)standard coordinates are precisely defined as(0.33,0.33)of pure white emission,providing a universal reference for evaluating white light accuracy and consistency across lighting and display technologies[5].To meet the requirements of high color-purity,most of the reported white emissive materials and WOLETs have been achieved by rational combination of red,green,blue for three primary colors or blue and orange for two complementary colors emitters[6],such as doping an emitter into an appropriate host and employing the multi-component active layers with a stacked configuration[7].Although a minority of doped electroluminescent devices have the capability of good exciton utilization to realize the white emission,the multi-component active layer is inherently prone to phase separation,which is harmful for the optoelectronic devices[4].Therefore.

Bipolar Thermally Activated Delayed Fluorescence Emitter with Balanced Carrier Transport for High-Efficiency Nondoped Green Electroluminescent Devices

High-efficiency electroluminescent devices featuring simplified architecture have received considerable attention due to significant advantages in construction procedures and commercialized applications.However,there still remains a critical challenge with regard to the lack of organic semiconductors that simultaneously possess high luminescent efficiency and balanced carrier-transporting abilities.Herein,we design a thermally activated delayed fluorescence(TADF)emitter 4-(9,9-dimethyl-9,10-dihydroacridine)-4′-triphenylphosphineoxide-benzophenone(DMAC-BPTPO)by incorporating triphenylphosphine oxide into the donor–acceptor skeleton.The accessional electrontransporting moiety,rod-like dimer,and horizontally packing model synergistically enable DMAC-BP-TPO which possesses an excellent photoluminescence quantum yield of nearly 90%with a reverse intersystem crossing rate constant of 2.0×106 s−1,horizontal dipole ratio of 89%,and a balanced electron and hole mobilities with a small constrast ratio of 1.08.Eventually,simplified electroluminescent devices including organic lightemitting diodes(OLEDs)and organic light-emitting transistors(OLETs)incorporating DMAC-BP-TPO-based nondoped film are demonstrated due to their superior integrated optoelectronic properties along with preferable horizontal dipole orientation.A record-high external quantum efficiency value of 21.7%and 4.4%are finally achieved in the simplified nondoped OLED and OLET devices,which are among the highest values in the related research fields.This work provides a new avenue to develop a high-efficiency bipolar TADF emitter to advance the simplified electroluminescent devices.

可控掺杂双极性半导体聚合物应用于简化构筑综合性能优异的有机逻辑电路

有机电子学的最终目标是实现简单地构筑高性能逻辑电路以满足各种应用需求.双极性有机半导体,特别是双极性共轭聚合物,在制备可溶液印刷、低成本和大面积的有机电路方面具有独特的优势.然而,本征双极性聚合物的窄带隙导致其电流开关比低(通常为10~2-10~3),阻碍了输出信号的高精度和抗干扰性,而这是潜在逻辑电路应用的关键要求.本文中,基于可控掺杂的工艺,本征平衡双极性聚合物实现了准单极传输特性,其p沟道和n沟道薄膜晶体管的电流开关比均显著提高至10~5-10~7.此外,可控掺杂的有机逻辑电路如非门、或非门、与非门通过直写印刷技术构建,其具有优异的综合性能,高达150的增益值和68%的信号噪声容限以及快速响应.本工作通过掺杂策略显著地提高了双极性材料的开关比,可为双极性材料在印刷集成电路中的实际应用提供理论基础.

Highly Fluorescent Semiconducting Two-Dimensional Conjugated Polymer Films Achieved by Side-Chain Engineering Showing Large Exciton Diffusion Length

Semiconducting two-dimensional conjugated polymers(2DCPs)with strong fluorescence emission have great potential for various optoelectronic applications.However,it is enormously challenging to achieve this goal due to the significant compact interlayerπ-πstacking-induced quenching effect in these systems.In this work,we found that highly fluorescent semiconducting 2DCPs can be prepared through an effective side-chain engineering approach in which interlayer spacers are introduced to reduce the fluorescence quenching effect.The obtained two truxene-based 2DCP films that,along with-C6H13 and-C_(12)H_(25)alkyl side chains as interlayer spacers both demonstrate superior fluorescence properties with a high photoluminescence quantum yield of 5.6%and 14.6%,respectively.These are among the highest values currently reported for 2DCP films.Moreover,an ultralong isotropic quasi-twodimensional exciton diffusion length constrained in the plane with its highest value approaching 110 nm was revealed by the transient photoluminescence microscopy technique,suggesting that theπ-conjugated structure in these truxene-based 2DCP films has effectively been extended.This work can enable a broad exploration of highly fluorescent semiconducting 2DCP films for more deeply fundamental properties and optoelectronic device applications.

High carrier mobility and strong fluorescence emission: Toward highly sensitive single-crystal organic phototransistors

Organic single crystals(OSCs)offer a unique combination of both individual and collective properties of the employed molecules,but it remains highly challenging to achieve OSCs with both high mobilities and strong fluorescence emissions for their potential applications in multifunctional optoelectronics.Herein,we demonstrate the design and synthesis of two novel triphenylamine-functionalized thienoacenes-based organic semiconductors,4,8-distriphenylamineethynylbenzo[1,2-b:4,5-b′]dithiophene(4,8-DTEBDT)and 2,6-distriphenylamineethynylbenzo[1,2-b:4,5-b′]dithiophene(2,6-DTEBDT),with high-mobility and strong fluorescence emission.The two compounds show the maximum mobilities up to 0.25 and 0.06 cm^(2) V^(-1) s^(-1),the photoluminescence quantum yields(PLQYs)of 51% and 45%,and the small binding energies down to 55.13 and 58.79 meV.The excellent electrical and optical properties ensured the application of 4,8-DTEBDT and 2,6-DTEBDT single crystals in ultrasensitive UV phototransistors,achieving high photoresponsivity of 9.60×105 and 6.43×10^(4) AW^(-1),and detectivity exceeding 5.68×10^(17) and 2.99×10^(16) Jones.

太阳光照下酞菁类有机半导体光催化C-H活化合成联芳基功能材料

有机共轭功能材料由于具有优异的光学和电学性能在有机光电子学领域备受关注和研究.发展简单、高效、绿色的有机功能材料合成方法是该领域研究中的一个重要课题.本研究发展了一种通过酞菁类有机半导体材料作为催化剂光催化C–H活化合成联芳基类功能材料的绿色方法.以酞菁类半导体材料为光催化剂,采用日常生活中最常见的清洁能源太阳光为光源,实现了室温下通过光催化直接C–H活化的方式合成联芳基化合物.研究发现, TiOPc(酞菁氧钛)半导体材料的催化活性最高,且对不同的芳基功能团展现了良好的催化活性.并以TiOPc作为光催化剂,合成了具有常见蒽类骨架结构的半导体功能材料,拓展了有机半导体功能材料的合成途径.

Molecular-scale integrated multi-functions for organic lightemitting transistors

Organic light-mitting transistors(OLETs)integrate the functions of light-emitting diodes and field-effect transistors into a unique device,opening a new door for optoelectronics.However,there is still a challenge due to the absence of high quality organic semiconductors for OLETs.Herein,we reported a novel molecule 2,6-di(anthracen-2-yl)naphthalene(2,6-DAN),which exhibited mobility of up to 19 cm2:V'-s'and an absolute fluorescence quantum yield of 37.09%,which are good values for organic semiconductors.Moreover,OLETs based on 2,6-DAN single crystals showed bright yellowish-green emission and well-balanced ambipolar charge transport.The excellent ratio of hole to electron mobilty can reach up to 0.86,which is superior to most single component OL ETs in typical device configurations reported so far.

High performance organic transistors and phototransistors based on diketopyrrolopyrrole-quaterthiophene copolymer thin films fabricated via low-concentration solution processing

Conjugated polymers have received considerable attentions over the past years due to their large-area potential applications via low-cost solution processing. Improving crystallinity of conjugated polymer molecules in solution-processed thin films is crucial for their efficient charge transport and thus high performance optoelectronic devices. Herein, with diketopyrrolopyrrole-quaterthiophene （PDQT） copo/ymer as an example, it is found that by simply reducing the solution concentration for spincoating meanwhile with the assistance of post-annealing, significantly enhanced film crystallinity with formation of typical single crystalline domains is obtained, which benefits from the enough space for better molecular assembly especially at the semiconductor/dielectric interface. High performance polymer transistors and phototransistors were finally constructed based on the optimal lowconcentration （2 mg/mL） spin-coated PDQT films （～12 nm）, which giving a high charge carrier mobility of 2.28 cm2 V-1 s-1 and a photoresponse on/off ratio of 2.1 ×107 at VG = 0 V under white light irradiation of 6mW/cm2. The results suggest that the bright future of PDQT crystalline films for large-area flexible integrated optoelectronic devices and the application of effective low-concentration processing approach in solution-processed organic electronics with reduced material waste.

Multi-walled carbon nanotubes covalently functionalized by axially coordinated metal-porphyrins： Facile syntheses and temporally dependent optical performance

Axially coordinated metal-porphyrin-functionalized multi-walled carbon nanotube （MWCNT） nanohybrids were prepared via two different synthetic approaches （a one-pot 1,3-dipolar cycloaddition reaction and a stepwise approach that involved 1,3-dipolar cycloaddition followed by nucleophilic substitution）, and characterized through spectroscopic techniques. Attachment of the tin porphyrins to the surface of the MWCNTs significantly improves their solubility and ease of processing. These axially coordinated （5,10,15,20-tetraphenylporphyrinato）tin（Ⅳ） （SnTPP）- MWCNTs exhibit significant fluorescence quenching. The third-order nonlinear optical properties of the resultant nanohybrids were studied by using the Z-scan technique at 532 nm with both nanosecond and picosecond laser pulses. The results show that the nanohybrids exhibit significant reverse saturable absorption or saturable absorption when nanosecond or picosecond pulses, respectively, are employed. Improvement in the nanosecond regime nonlinear absorption is observed on proceeding to the nanohybrids and is ascribed to a combination of the outstanding properties of MWCNTs and the chemically attached metal-porphyrins.

Organic single-crystal phototransistor with unique wavelength-detection characteristics

Organic phototransistors based on high-quality 2,8-dichloro-5,11-dihexyl-indolo[3,2-b]carbazo(CHICZ)single crystals show the highest photoresponsivity of 3×10^3 A W^-1, photosensitivity of 2×10^4 and the detectivity can achieve 8.4×10^14 Jones. We also discovered good linear dependence of log(photosensitivity) versus the wavelength when the devices were illuminated with a series of sameintensity but different-wavelength lights. The organic phototransistors based on CHICZ single crystal have potential applications in wavelength-detection.

Well-balanced ambipolar diketopyrrolopyrrole-based copolymers for OFETs,inverters and frequency doublers

Conjugated polymers with well-balanced ambipolar charge transport is essential for organic circuits at low cost and large area with simplified fabrication techniques.Aiming at this point,herein,a novel asymmetric thiophene/pyridine-flanked diketopyrrolopyrrole-based copolymer(PPyTDPP-2FBT)is designed and synthesized.Due to the effect of incorporating F atoms on molecular energy alignment and conjugation conformation,the PPyTDPP-2FBT copolymer exhibits typical V-shaped ambipolar field-effect transfer characteristics with well-balanced hole and electron mobilities of 0.64 and 0.46 cm^(2)V^(−1)s^(−1),respectively.Furthermore,organic digital and analog circuits such as inverters and frequency doublers are successfully constructed based on solution-processed films of the PPyTDPP-2FBT copolymers which show a typical circuit operating mode with a high gain of 133 due to the well-balanced electrical properties.In addition,PPyTDPP-2FBT-based devices also demonstrate good stability and batch repeatability,suggesting their great potential applications in organic integrated electronic circuits.

Ultrathin silica film derived with ultraviolet irradiation of perhydropolysilazane for high performance and low voltage organic transistor and inverter

In recent years, organic electronic devices have become more and more popular, such as organic solar cell （OSC） [1-4], organic light emitting diode （OLED） [5-7] and organic thin film transistor （OTFT） [8-11] by virtue of their light weight, easy-processing and flexibility.

Carbon nanotubes assisting interchain charge transport in semiconducting polymer thin films towards much improved charge carrier mobility

Conjugated polymers attracted much attention in the past few decades due to their wide applications in various optoelectronic devices and circuits. The charge transport process in conjugated polymers mainly occurs in the intrachain and interchain parts, where the interchain charge transport is generally slower than intrachain transport and may slow down the whole charge transport properties. Aiming at this issue, herein we employ semiconducting single-walled carbon nanotubes(s-SWNTs) as efficient charge-transporting jointing channels between conjugated polymer chains for improving the charge transport performance. Taking the typical conjugated polymer, ploy-N-alkyl-diketopyrrolopyrrole-dithienylthieno[3,2-b]thiophene(PDPP-TT) as an example, polymer thin film transistors(PTFTs) based on the optimized blended films of PDPP-TT/s-SWNTs exhibit an obviously increasing device performance compared with the devices based on pure PDPP-TT films, with the hole and electron mobility increased from 2.32 to 12.32 cm^2 V^-1 s^-1 and from 2.02 to 5.77 cm^2 V^-1 s^-1, respectively. This result suggests the importance of forming continuous conducting channels in conjugated polymer thin films, which can also be extended to other polymeric electronic and optoelectronic devices to promote their potential applications in large-area, low-cost and high performance polymeric electronic devices and circuits.

Polymorph and anisotropic Raman spectroscopy of Phz-Hca cocrystals

The nucleation and growth mechanism and polymorph-property correlations in the molecular cocrystal field are widely sought but currently remain unclear. Herein, a new wire-like morphology of phenazine(Phz)-chloranilic acid(H2ca) cocrystal(PHC) is demonstrated for the first time, and the self-assembly of Phz and H2ca is controlled to selectively prepare kinetically stable wires and thermodynamically stable plates. Specifically, low precursor concentration is beneficial for one-dimensional(1D) self-assembly along the [010] crystallographic direction, while only supersaturation can trigger 2D self-assembly along the [100] and [010] directions, respectively. This is understandable in terms of the(020) face showing the largest attachment energy(Eatt) and the(002) face possessing the smallest surface energy(Esurf). Moreover, anisotropic Raman spectra related to the mode symmetry and atomic displacements in two types of PHCs are revealed, and the same Raman-active vibrational bands of PHC wire and plate show different polarization responses, which is intrinsically ascribed to their different molecular orientations.Overall, this is the first case that morphologies of cocrystal are precisely tuned with comprehensive investigations of their anisotropic vibrational characteristics.

Vertical‐organic‐nanocrystal‐arrays for crossbar memristors with tuning switching dynamics toward neuromorphic computing

Memristors proposed by Leon Chua provide a new type of memory device for novel neuromorphic computing applications.However,the approaching of distinct multi‐intermediate states for tunable switching dynamics,the con-trolling of conducting filaments(CFs)toward high device repeatability and reproducibility,and the ability for large‐scale preparation devices,remain full of challenges.Here,we show that vertical‐organic‐nanocrystal‐arrays(VONAs)could make a way toward the challenges.The perfect one‐dimensional structure of the VONAs could confine the CFs accurately with fine‐tune resistance states in a broad range of 103 ratios.The availability of large‐area VONAs makes the fabrication of large‐area crossbar memristor arrays facilely,and the analog switching characteristic of the memristors is to effectively imitate different kinds of synaptic plasticity,indicating their great potential in future applications.

Unveiling the role of Fe_(3)O_(4)in polymer spin valve near Verwey transition

The spinterface formed between ferromagnetic(FM)electrode and organic materials is vital for performance optimization in organic spin valve(OSV).Half-metallic Fe_(3)O_(4)with drastic change in structure,conductivity and magnetic property near Verwey transition can serve as an intrinsic spinterface regulator.However,such modulating effect of Fe_(3)O_(4)in OSV has not been comprehensively investigated,especially below the Verwey transition temperature(Tv).Here,we highlight the important role of Fe_(3)O_(4)electrode in reliable-working and controllable Fe_(3)O_(4)/P3HT/Co polymer spin valves by investigating the magnetoresistance(MR)above and below 7V.In order to distinguish between different contributions to charge transport and related MR responses,the systematic electronic and magnetic characterizations were carried out in full temperature range.Particularly,the first-order metal-insulator transition in Fe_(3)O_(4)has a dramatic effect on the MR enhancement of polymer spin valves at 7V.Moreover,both the conducting mode transformation and MR line shape modulation could be accomplished across 7V.This research renders unique scenario to multimodal storage by external thermodynamic parameters,and further reveals the importance of spin-dependent interfacial modification in polymer spin valves.

Comparable charge transport property based on S…S interactions with that of π-π stacking in a bis-fused tetrathiafulvalene compound

Compact molecular packing with short π-π stacking and large π-overlap in organic semiconductors is desirable for efficient charge transport and high carrier mobility. Thus charge transport anisotropy along different directions is commonly observed in organic semiconductors. Interestingly, in this article, we found that comparable charge transport property were achieved based on the single crystals of a bis-fused tetrathiafulvalene derivative （EM-TTP） compound along two interaction directions, that is, the multiple strong S…S intermolecular interactions and the π-π stacking direction, with the measured electrical conductivity and hole mobility of 0.4 S cm-1, 0.94 cm2 V i s 1 and 0.2 S cm-1, 0.65 cm2 V-1 s-1, respectively. This finding provides us a new molecular design concept for developing novel organic semiconductors with isotropic charge transport property through the synergistic effect of multiple intermolecular interactions （such as π-π interactions） and π-π stacking.

Two-dimensional conjugated polymers synthesized via on-surface chemistry

Two-dimensional materials(2DMs)are an important subject in material science that have many interesting physical properties and significant potential applications in various technological areas[1,2].

Hexyl substitution of pentathienoacene toward a significant improvement in charge transport

A novel semiconductor, dihexyl-substituted pentathienoacene(C6-PTA) is designed and synthesized in five steps with the total yield up to 25.2%. The introduction of hexyl chains endow the thin film semiconductor with about threefold increase in carrier mobility and one to three orders of magnitude improvement in current on/off ratio. Furthermore, single crystal FETs based on C6-PTA exhibited mobility up to 0.64 cm^2 V^(-1) s^(-1), which is over 50 times higher than the thin film counterpart. The results indicate clearly that C6-PTA is a promising organic semiconductor with high stability.

Tuning the aggregation structure and electrical property of 2.6-diphenyl-anthracene by the density of octadecyltrichlorosilane

The physical and chemical properties of organic semiconductors are closely related to their aggregation structure. Tuning of aggregation structure and electrical property is important for the application in organic electronics. In this study, a facile way to tune the aggregation structure and electrical property of 2.6-diphenyl-anthracene(DPA) is realized by using the octadecyltrichlorosilane(OTS) modification layer with different density which is fabricated by controlling reaction temperature and time.Compared with low density OTS, DPA forms larger grain size, less grain boundaries, and better molecular ordering on high density OTS surface. As a result, the charge transporting mobility of DPA film on high density OTS surface is about two orders of magnitude higher than that on low density OTS surface. The tunable aggregation structure and electrical property of DPA demonstrated here would be meaningful for the application of DPA in organic electronics.