Ambipolar Organic Semiconductors Research Articles

Highly Soluble Ambipolar anti-Perylene-3,4 : 9,10-bis(benzimidazole)s Stabilize a Room-Temperature Columnar Hexagonal Phase.

A new series of highly soluble perylene anti-bis(4,5-dialkoxybenzimidazole)s bearing branched flexible chains stabilizing room temperature columnar hexagonal phase and with balanced ambipolar charge carrier mobility is reported for the first time. Only the anti isomer was successfully separated and characterized. These compounds have a high extinction coefficient, small optical band gap and wide absorption range, thus making them a promising class of ambipolar organic semiconductors capable of self-organizing.

Dibenzothiophene Sulfone‐Based Ambipolar‐Transporting Blue‐Emissive Organic Semiconductors Towards Simple‐Structured Organic Light‐Emitting Transistors

AbstractThe development of blue‐emissive ambipolar organic semiconductor is an arduous target due to the large energy gap, but is an indispensable part for electroluminescent device, especially for the transformative display technology of simple‐structured organic light‐emitting transistor (SS‐OLET). Herein, we designed and synthesized two new dibenzothiophene sulfone‐based high mobility blue‐emissive organic semiconductors (DNaDBSOs), which demonstrate superior optical property with solid‐state photoluminescent quantum yield of 46–67 % and typical ambipolar‐transporting properties in SS‐OLETs with symmetric gold electrodes. Comprehensive experimental and theoretical characterizations reveal the natural of ambipolar property for such blue‐emissive DNaDBSOs‐based materials is ascribed to a synergistic effect on lowering LUMO level and reduced electron injection barrier induced by the interfacial dipoles effect on gold electrodes due to the incorporation of appropriate DBSO unit. Finally, efficient electroluminescence properties with high‐quality blue emission (CIE (0.179, 0.119)) and a narrow full‐width at half‐maximum of 48 nm are achieved for DNaDBSO‐based SS‐OLET, showing good spatial control of the recombination zone in conducting channel. This work provides a new avenue for designing ambipolar emissive organic semiconductors by incorporating the synergistic effect of energy level regulation and molecular‐metal interaction, which would advance the development of superior optoelectronic materials and their high‐density integrated optoelectronic devices and circuits.

Dibenzothiophene Sulfone-Based Ambipolar-Transporting Blue-Emissive Organic Semiconductors Towards Simple-Structured Organic Light-Emitting Transistors.

The development of blue-emissive ambipolar organic semiconductor is an arduous target due to the large energy gap, but is an indispensable part for electroluminescent device, especially for the transformative display technology of simple-structured organic light-emitting transistor (SS-OLET). Herein, we designed and synthesized two new dibenzothiophene sulfone-based high mobility blue-emissive organic semiconductors (DNaDBSOs), which demonstrate superior optical property with solid-state photoluminescent quantum yield of 46-67 % and typical ambipolar-transporting properties in SS-OLETs with symmetric gold electrodes. Comprehensive experimental and theoretical characterizations reveal the natural of ambipolar property for such blue-emissive DNaDBSOs-based materials is ascribed to a synergistic effect on lowering LUMO level and reduced electron injection barrier induced by the interfacial dipoles effect on gold electrodes due to the incorporation of appropriate DBSO unit. Finally, efficient electroluminescence properties with high-quality blue emission (CIE (0.179, 0.119)) and a narrow full-width at half-maximum of 48 nm are achieved for DNaDBSO-based SS-OLET, showing good spatial control of the recombination zone in conducting channel. This work provides a new avenue for designing ambipolar emissive organic semiconductors by incorporating the synergistic effect of energy level regulation and molecular-metal interaction, which would advance the development of superior optoelectronic materials and their high-density integrated optoelectronic devices and circuits.

Controllable-doping ambipolar conjugated polymeric semiconductors towards simplified-constructed organic logic circuits with excellent comprehensive performance

Organic electronics aims to simplify the construction of high-performance basic logic circuits for various applications. Ambipolar organic semiconductors, particularly ambipolar conjugated polymers, offer distinct advantages of easy solution-printing-based fabrication and low-cost development of large-area organic circuits. However, the narrow bandgaps of intrinsic ambipolar polymers result in the low current on/off ratio (generally 102–103), impeding the generation of output signals with high accuracy and immunity, which are critical requirements for potential logic circuit applications. The quasi-unipolar transport properties for pristine well-balanced ambipolar polymers were obtained using a controllable-doping process, which resulted in a significant increase in current on/off ratios (105–107) for both p-channel and n-channel thin-film transistors. Furthermore, large-area organic logic circuits such as NOT, NOR, and NAND gates were constructed using a direct writing technique based on the same ambipolar conjugated polymer films with superior p- and n-conducting channels by the controllable-doping process, demonstrating excellent overall performance with a high gain value of ∼150, signal noise margins of 68% and fast response to input voltages. This study provides valuable guidelines for improving the on/off ratio of ambipolar materials by implementing the doping strategy, further promoting the possibility of practical applications in solution-printed integrated organic circuits.

Complementary Inverter Based on n‐Type and p‐Type OFETs with the Same Ambipolar Organic Semiconductor and ITO S/D Electrodes

AbstractBottom‐gate and bottom‐contact n‐type and p‐type organic field‐effect transistors (OFETs) are simultaneously obtained by combining the ambipolar semiconductor film of diketopyrrolopyrrole‐based conjugated polymer (P4FTVT‐C32) with indium tin oxide (ITO) source/drain (S/D) electrodes. P4FTVT‐C32 thin film exhibits n‐type unipolar property with the low work functional (WF) ITO S/D electrodes modified by polyethylenimine ethoxylated (PEIE) and it exhibits p‐type unipolar property with the high WF ITO S/D electrodes modified by HCl:InCl3. Hence, complementary inverters with transition voltages near VDD/2 and the maximum gain of 138 converting “1” state input into “0” state output are achieved by two different modifications via screen printing on ITO electrodes and then, only one‐time bar coating of P4FTVT‐C32. To further improve the performance and the uniformity of the OFET devices, the modification of octadecyltrichlorosilane (OTS) is also introduced. This work provides an easy‐handling method for the fabrication of low‐cost, high performance organic electronic devices and integrated circuits.

基于6,13-双氰基并五苯一维滑移堆积微米带状晶体 的双极性电荷传输

Featuring small charge transport scattering, mesoscale size, and easy fabrication, one-dimensional self-assembled micro/nanomaterials (1D-MNMs) based on organic π-conjugated systems can be facilely incorporated into integrated microcircuits. Although tremendous progress has been made in 1D-MNMs based on p- or n-channel organic semiconductors, examples of lD-MNMs based on ambipolar organic semiconductors are scarce. Herein, we achieved a novel 1D-MNM based on 6,13-dicyanopentacene (DCP) with a 1D slipped stacking motif using the physical vapor transport method. The DCP-based 1D-MNM showed outstanding, well-balanced ambipolar charge transport with electron and hole mobilities of up to 0.34 and 0.38 cm2 V−1 s−1, respectively, which are among the best ambipolar transport characteristics of 1D-MNMs. Furthermore, a complementary inverter based on the ambipolar 1D-MNM of DCP was also constructed with a gain of up to 7, indicating potential application in organic logic circuits.

Recent advances in n-type and ambipolar organic semiconductors and their multi-functional applications.

Organic semiconductors have received broad attention and research interest due to their unique integration of semiconducting properties with structural tunability, intrinsic flexibiltiy and low cost. In order to meet the requirements of organic electronic devices and their integrated circuits, p-type, n-type and ambipolar organic semiconductors are all necessary. However, due to the limitation in both material synthesis and device fabrication, the development of n-type and ambipolar materials is quite behind that of p-type materials. Recent development in synthetic methods of organic semiconductors greatly enriches the range of n-type and ambipolar materials. Moreover, the newly developed materials with multiple functions also put forward multi-functional device applications, including some emerging research areas. In this review, we give a timely summary on these impressive advances in n-type and ambipolar organic semiconductors with a special focus on their synthesis methods and advanced materials with enhanced properties of charge carrier mobility, integration of high mobility and strong emission and thermoelectric properties. Finally, multi-functional device applications are further demonstrated as an example of these developed n-type and ambipolar materials.

Oxadiazole-integrated heterocoronene discotics as ambipolar organic semiconductors

Disc-shaped liquid crystals designed by introducing oxadiazole functional units into a heterocoronene system were explored in thin-film space-charge limited current (SCLC) devices. They were found to exhibit ambipolar semiconducting behavior.

Ambipolar Nickel Dithiolene Complex Semiconductors: From One- to Two-Dimensional Electronic Structures Based upon Alkoxy Chain Lengths.

Air-stable single-component ambipolar organic semiconductors that conduct both holes and electrons are highly desired but have been rarely realized. Neutral nickel bis(dithiolene) complexes are promising candidates that fulfill the stringent electronic requirements of shallow HOMO levels and deep LUMO levels, which can reduce the carrier injection barrier to overcome the work function of gold electrodes and ensure air stability. However, most nickel bis(dithiolene) analogs that have been characterized as ambipolar semiconductors have twisted molecular structures that hinder the effective intermolecular interactions required for carrier conduction. To address this issue, we synthesized planar alkoxy-substituted nickel bis(dithiolene) analogs that facilitate dense packing with effective intermolecular interactions. Remarkably, changing the methoxy substituents to ethoxy or propoxy groups led to a dramatic change in the packing mode, from one-dimensional to herringbone-like, while maintaining effective intermolecular interactions. These materials overcome the usual trade-off between crystallinity and solubility; they are highly crystalline, even in their film forms, and are highly soluble in organic solvents. They are therefore readily solution-processable to form semiconducting layers with well-defined and well-ordered structures in field-effect transistors. Devices based on these compounds exhibited efficient ambipolar characteristics, even after several months of exposure to air, achieving high carrier mobilities of up to 10-2 cm2 V-1 s-1 and large on/off ratios of up to 105, which are the top-class performances achieved for a single-component ambipolar semiconductor material driven in air.

Selective doping of a single ambipolar organic semiconductor to obtain P- and N-type semiconductors

•A well-balanced ambipolar organic semiconductor is synthesized as host semiconductor •Proper doping of the single host semiconductor yields both p- and n-type semiconductors •Organic PN homojunctions and corresponding photodiodes are constructed and characterized The idea of acquiring p- and n-type organic semiconductors (OSCs) through controllable doping of a single OSC is highly attractive. However, realization of this idea remains challenging due to the difficulties in achieving effective p- and n-doping on a single OSC simultaneously. Herein, by synthesizing a solution-processable conjugated polymer with well-balanced ambipolar transport as the host semiconductor and using appropriate dopants, we demonstrate the feasibility of obtaining p- and n-type OSCs from a single OSC. The successful doping control of the polarity and electrical property of the OSC is confirmed by electrical characterizations on doped films and devices. Then, solution-processed organic PN homojunctions based on the p- and n-doped OSC films are constructed, which provide good platforms for studying organic semiconductor physics and for fabricating functional devices like photodiodes. The results provide a paradigm for utilizing doping technique in organic semiconductor devices similar to that in silicon-based devices. The idea of acquiring p- and n-type organic semiconductors (OSCs) through controllable doping of a single OSC is highly attractive. However, realization of this idea remains challenging due to the difficulties in achieving effective p- and n-doping on a single OSC simultaneously. Herein, by synthesizing a solution-processable conjugated polymer with well-balanced ambipolar transport as the host semiconductor and using appropriate dopants, we demonstrate the feasibility of obtaining p- and n-type OSCs from a single OSC. The successful doping control of the polarity and electrical property of the OSC is confirmed by electrical characterizations on doped films and devices. Then, solution-processed organic PN homojunctions based on the p- and n-doped OSC films are constructed, which provide good platforms for studying organic semiconductor physics and for fabricating functional devices like photodiodes. The results provide a paradigm for utilizing doping technique in organic semiconductor devices similar to that in silicon-based devices.

Cyanophenoxy-Substituted Silicon Phthalocyanines for Low Threshold Voltage n-Type Organic Thin-Film Transistors

Silicon phthalocyanines (SiPcs) are a class of n-type or ambipolar organic semiconductors that have been incorporated into organic thin-film transistors (OTFTs), organic light-emitting diodes (OLEDs), and organic photovoltaics (OPVs). Despite a relatively large catalogue of previously reported SiPc materials, fabricated OTFTs with these materials typically have threshold voltages (VT) above 10 V, limiting their usage in commercial devices due to exceedingly high power consumption. Recent studies have suggested that the VT can be reduced in OTFTs prepared from phenoxy-substituted SiPcs by introducing electron-withdrawing groups onto the phenoxy moieties. Herein, we report the synthesis and characterization of three SiPcs with phenoxy axial substituents containing nitrile and fluorine functional groups. These SiPcs, along with 3,5-difluorophenoxy SiPc were evaluated as candidate materials for n-type OTFTs. We found that further increasing the electron-withdrawing character of the pendant phenoxy groups of the SiPc resulted in a significant decrease in average VT with the lowest reported value being 4.8 V, the lowest VT reported for a phenoxy-SiPc-based OTFT exceeding the previous record low of 7.8 V attributed to F10-SiPc. This decrease in VT could be directly correlated to the Hammett parameter of the axial functional groups. Furthermore, it was noted that dewetting occurred when the phenoxy pendant group of the SiPc was substituted at the para position with a nitrile group combined with ortho- or meta-substituted fluorines, which was attributed to interactions at the semiconductor/dielectric interface. Depositing these SiPcs on silane-terminated poly(styrene) brush modified substrates improved long-term stability, demonstrated by a minimal change in surface morphology according to atomic force microscopy (AFM) images.

Butterfly-like Shape Liquid Crystals Based Fused-Thiophene as Unidimensional Ambipolar Organic Semiconductors with High Mobility.

Mesomorphous butterfly-like shape molecules based on benzodithiophene, benzodithiophene-4,8-dione and cyclopentadithiophen-4-one core moieties were efficiently synthesized by the Suzuki-Miyaura coupling and Scholl oxidative cyclo-dehydrogenation reactions' tandem. Most of the butterfly molecules spontaneously self-organize into columnar hexagonal mesophase. The electron-deficient systems possess strong solvent-gelling ability but are not luminescent, whereas the electron-rich terms do not form gels but strongly emit light between 400 and 600 nm. The charge carrier mobility was also measured by time-of-flight transient photocurrent technique in the mesophases for some of the compounds. They display hole-transport performances with positive charge mobility in the 10-3 cm-2 V-1 s-1 range, consistent with the high degree of ordering and stability of the columnar superstructures. In particular, the mesogen with a benzodithiophen-4,8-dione core shows ambipolar charge carrier transport with both high electron (μe =6.6×10-3 cm-2 V-1 s-1 ) and hole (μh =4.5×10-3 cm-2 V-1 s-1 ) mobility values.

Charge transfer properties of imide-functionalized thiazole-based oligomers: Roles of oligomer length, thiophene donor, and fluorine-substitution

Three series of oligomers containing functionalized imide and thiophene rings, namely the acceptor type bisthiazole imide oligomer with different length (PBTzIn, n = 1–8), the donor-acceptor type derivatives by introducing three electron donating thiophene rings into BTzI (PBTzI3Tm, m = 1–4), and derivatives by substituting the two hydrogen of center thiophene in PBTzI3Tm with fluorine (PBTzI3T-2Fm, m = 1–4), were designed based on some experimentally synthesized oligomers to clarify the roles of oligomer length, thiophene donor, and fluorine-substitution on the charge transfer properties. The charge transfer properties of these imide-functionalized thiazole-based oligomers were systematically studied using density functional theory and traditional Marcus theory in term of geometric structures, frontier molecular orbitals, ionization potentials (IP), electron affinities (EA), reorganization energies, charge transfer integrals, crystal packing models, and charge transfer mobilities. The IP/EA decreased/increased with increasing oligomer length in PBTzIn, rendering long PBTzIn oligomers showing both p- and n-type characteristic of organic semiconductors. The orbital energy level and mobility show saturation characteristics for n = 6.PBTzI8 shows high and balanced hole/electron mobility of 1.089/0.249 cm2 V−1s−1 and thus is good ambipolar semiconductor. The introduced three thiophene rings in PBTzI3Tm (m = 1–4) enhances the backbone conjugate property and reduces the hole injection barrier. Substituting thiophene H atoms with F further enhances the interaction between the non-covalent bond N…S and S…F and thus increases the molecular planarity, rendering PBTzI3T-2Fm (m = 1–4) being better semiconductor. PBTzI3T3 is ambipolar organic semiconductor with hole/electron mobility of 11.760/1.396 cm2V−1s−1, while PBTzI3T-2F3 and PBTzI3T-2F4 show better ambipolar organic semiconductor performance with much larger hole/electron mobility of 16.325/3.674 cm2V−1s−1 and 60.019/5.086 cm2V−1s−1.

\u03c0-Extended perylene diimide double-heterohelicenes as ambipolar organic semiconductors for broadband circularly polarized light detection

Despite great challenges, the development of new molecular structures with multiple and even conflicting characteristics are eagerly pursued for exploring advanced applications. To develop high-performance chiral organic semiconducting molecules, a distorted π-system is required for strong coupling with circularly polarized light (CPL), whereas planar π-stacking systems are necessary for high charge-carrier mobility. To address this dilemma, in this work, we introduce a skeleton merging approach through distortion of a perylene diimide (PDI) core with four fused heteroaromatics to form an ortho-π-extended PDI double-[7]heterohelicene. PDI double helicene inherits a high dissymmetry factor from the helicene skeleton, and the extended π-planar system concurrently maintains a high level of charge transport properties. In addition, ortho-π-extension of the PDI skeleton brings about near-infrared (NIR) light absorption and ambipolar charge transport abilities, endowing the corresponding organic phototransistors with high photoresponsivity of 450 and 120 mA W−1 in p- and n-type modes respectively, along with a high external quantum efficiency (89%) under NIR light irradiations. Remarkably, these multiple characteristics enable high-performance broadband CPL detections up to NIR spectral region with chiral organic semiconductors.

Silicon Phthalocyanines for n-Type Organic Thin-Film Transistors: Development of Structure–Property Relationships

Silicon phthalocyanines (SiPcs) have shown great potential as n-type or ambipolar organic semiconductors in organic thin-film transistors (OTFTs) and organic photovoltaics. Although properly design...

Design and Synthesis of Annulated Benzothiadiazoles via Dithiolate Formation for Ambipolar Organic Semiconductors.

Substituted 2,1,3-benzothiadiazole (BTD) is a widely used electron acceptor unit for functional organic semiconductors. Difluorination or annulation on the 5,6-position of the benzene ring is among the most adapted chemical modifications to tune the electronic properties, though each sees its own limitations in regulating the frontier orbital levels. Herein, a hitherto unreported 5,6-annulated BTD acceptor, denoted as ssBTD, is designed and synthesized by incorporating an electron-withdrawing 2-(1,3-dithiol-2-ylidene)malononitrile moiety via aromatic nucleophilic substitution of the 5,6-difluoroBTD (ffBTD) precursor. Unlike the other reported BTD annulation strategies, this modification leads to the simultaneous decrease in both frontier orbital energies, a welcoming feature for photovoltaic applications. Incorporation of ssBTD into conjugated polymers results in materials boasting broad light absorption, dramatic solvatochromic and thermochromic responses (>100 nm shift and a band gap difference of ∼0.28 eV), and improved crystallinity in the solid state. Such physical properties are in accordance with the combined electron-withdrawing effect and significantly increased polarity associated with the ssBTD unit, as revealed by detailed theoretical studies. Furthermore, the thiolated ssBTD imbues the polymer with ambipolar charge transport property, in contrast to the ffBTD-based polymer, which transports holes only. While the low mobilities (10-4 to 10-5 cm2 V-1 s-1) could be further optimized, detailed studies validate that the thioannulated BTD is a versatile electron-accepting unit for the design of functional stimuli-responsive optoelectronic materials.

Improving Both Electron and Hole Mobilities of an Ambipolar Polymer by Integrating Sodium Sulfonate‐Tethered Alkyl Side Chains†

Summary of main observation and conclusionHigh performance ambipolar organic semiconductors are highly desirable for organic logic circuits. Herein, we demonstrate the integration of sodium sulfonate (SS)‐tethered sidechains into a diketopyrrolopyrrole‐based ambipolar polymer (PDPP3T) can simultaneously improve its hole and electron transport performances either parallel or perpendicular to polymer film. Three SS‐functionalized polymers (PDPP3T‐xSS, x = 0.025, 0.05 and 0.10) were synthesized and studied. It was found that SS functionalization can reinforce interchain π‐π interactions, slightly lower frontier orbital energy levels, produce more rod‐like structures in film, and change chain‐packing from edge‐on to face‐on fashion, but has little influence on thermal properties. More interestingly, organic field‐effect transistors reported hole mobility of 0.27 ± 0.066 cm2·V–1·s–1 and electron mobility of 0.038 ± 0.016 cm2·V–1·s–1 for PDPP3T, while increased 2.4 and 5 folds to 0.64 ± 0.087 and 0.19 ± 0.051 cm2·V–1·s–1 for PDPP3T‐0.025SS, respectively. Moreover, PDPP3T‐xSS devices displayed reduced threshold voltages for both hole and electron transports. Meanwhile, space charge‐limited current method found SS functionalization achieved an order of magnitude increase in electron mobility and slight enhancement in hole mobility transporting perpendicular to polymer film. In‐depth investigations suggest such enhancements may originate from the joint actions of chain‐stacking modulation and ionic doping effect.

A DFT study on the electronic and photophysical properties of biphenylyl/thiophene derivatives for organic light emitting transistors

A theoretical study was carried out to understand the geometrical, electronic and optical properties of bipheylyl/thiophene based molecular system. For that, density functional theory along with classical Marcus charge transfer theory and time-dependent potentials were used. The results indicate that the structure-property relationship between the molecular parameters and ionization energy, electron affinity, reorganization energy, charge transfer integrals, mobility, energy gap, optical absorption and transition dipole moments. Low lying HOMO values and lower bandgaps of the molecules offer a higher charge transport in the systems and 5,5″-bis(4-biphenylyl)-2,2′:5′,2″-terthiophene (BP3T) molecule shows the maximum hole and electron mobility, 0.81 cm2 V−1 S−1 and 0.17 cm2 V−1 S−1, respectively. The results have shown that all the title compounds can be fabricated as ambipolar organic semiconductor materials and can be considered for the fabrication of efficient organic light emitting transistors.

Ester-Flanked π-Extended Quinolines for Solution-Processable Ambipolar Organic Field-Effect Transistors

A series of π-extended quinolines with D−π–A–D and D−π–A–A architectures were designed and synthesized via the Sonagashira cross-coupling reaction to serve as ambipolar organic semiconductors for u...

Theoretical insights on the high and differential charge transfer performance of dithienyl-diketopyrrolopyrrole-based polymers as ambipolar semiconductors

Diketopyrrolopyrrole (DPP)-containing polymers are among the highest mobility semiconductors for field-effect transistor applications. The molecular geometries, electronic structures and charge transport properties as ambipolar organic semiconductors of two series of total 24 donor–acceptor dithienyl-diketopyrrolopyrrole-based oligomers mDTDPPAr and nBDTDPPAr (m = 1–4, n = 1–2, Ar = TT, BT, BDT, TVT) are investigated theoretically through density functional theory and classical Marcus charge transfer theory. The effects of oligomer length form = 1–4, different Ar groups, and different Ar position on the structures and charge transfer properties are systematically studied. It was found that expanding π-conjugate backbone is a viable method to improve their semiconductor performance. Oligomers 4DTDPPTT, 4DTDPPBT, 4DTDPPTVT possess prominent ambipolar semiconductors properties with charge transfer mobilities of 9.62, 10.73, 12.60 cm2 V−1 s−1 for hole and of 7.54, 8.06, 15.56 cm2 V−1 s−1 for electron, respectively. 4DTDPPBDT exhibits large but unbalanced ambipolar performance with hole/electron transfer mobilities of 10.86/20.17 cm2 V−1 s−1 due to the special conjugation of BDT. Changing the order and position of donor and acceptor units has less significant influence on charge transfer mobility. Anisotropic mobilities are also studied to clarify the different charge transfer directions.