Hexaazatriphenylene Hexacarbonitrile Research Articles

Multiple Redox‐Active Cyano‐Substituted Organic Compound Integrated with MXene Nanosheets for High‐Performance Flexible Aqueous Zn‐Ion Battery

AbstractAn eco‐friendly organic compound, with rich redox sites, considered a promising cathode material for aqueous zinc‐ion batteries (AZIBs). Despite its potential, limited specific capacity and cycle instability impede its practical application. Herein, an organic compound, hexaazatriphenylene hexacarbonitrile (6CN‐HAT), is designed with a π–π conjugated aromatic structure, and integrated with MXene nanosheets to construct a flexible self‐supporting electrode (6CN‐HAT@MXene). Ex‐situ characterizations and theoretical calculations verify that the charge storage mechanism predominantly involves coordination and non‐coordination reactions between reactive C═N and ─CN sites with cations. The introduction of MXene nanosheets not only bolster the stability and electronic conductivity of the 6CN‐HAT@MXene but also expose additional active sites for cation coordination. As a cathode material in AZIBs, 6CN‐HAT@MXene exhibits an outstanding discharge specific capacity of 413 mAh g−1 at 0.05 A g−1. Remarkably, even after 5000 cycles at 5 A g−1, the discharge capacity retained 91%. Furthermore, based on the 6CN‐HAT@MXene electrode, a flexible micro‐zinc‐ion batteries with high area capacity of 257.4 mF cm−2 is prepared using laser cutting technology, highlighting its potential for future applications in portable and wearable electronic devices.

Impact of Varying Position and Ratio of Charge Generation Layer on Performance Parameters of Organic Photodiode

Organic photodiodes have emerged as the best alternative to inorganic devices during the last decade. Herein, a highly efficient organic photodiode having charge generation layer (CGL) is demonstrated. This charge generation layer is a combination of HAT-CN (hexaazatriphenylene-hexacarbonitrile) and TAPC (1,1-bis[(di-4-tolyamino)phenyl)]cyclohexane) materials which generate electrons and holes, correspondingly. Moreover, in this work, the proposed device (D2) is compared with other four non-CGL (D1) and CGL based (D3, D4 and D5) devices. In all the CGL based devices, positional variation of the CGL layer is incorporated. In the proposed device (D2), the CGL is situated outside the active layer in such a manner like HAT-CN is placed near acceptor and TAPC is near donor layer. In this way, the proposed device is showing the remarkable improvements in terms of photocurrent and dark current as 134.2 nA and 10.2 nA, respectively. The value of photocurrent of D2 is 34 times increased of the reference device (D1). Furthermore, on comparing with other CGL based devices D3, D4 and D5, photocurrent of D2 is approx 1.6, 1.4 and 9 times enhanced, correspondingly. Moreover, the thickness optimization and internal analysis of the proposed device are also performed to show the novelty of the presented work.

Rare Guest-Induced Electrical Conductivity of Zn-Porphyrin Metallacage Inclusion Complexes Featuring π-Donor/Acceptor/Donor Stacks.

Charge-transfer (CT) interactions between co-facially aligned π-donor/acceptor (π-D/A) arrays engender unique optical and electronic properties that could benefit (supra)molecular electronics and energy technologies. Herein, we demonstrate that a tetragonal prismatic metal-organic cage (MOC18+) having two parallel π-donor tetrakis(4-carboxyphenyl)-Zn-porphyrin (ZnTCPP) faces selectively intercalate planar π-acceptor guests, such as hexaazatriphenylene hexacarbonitrile (HATHCN), hexacyanotriphenylene (HCTP), and napthanelediimide (NDI) derivatives, forming 1:1 πA@MOC18+ inclusion complexes featuring supramolecular π-D/A/D triads. The π-acidity of intercalated π-acceptors (HATHCN ≫ HCTP ≈ NDIs) dictated the nature and strength of their interactions with the ZnTCPP faces, which in turn influenced the binding affinities (Ka) and optical and electronic properties of corresponding πA@MOC18+ inclusion complexes. Owing to its strongest CT interaction with ZnTCPP faces, the most π-acidic HATHCN guest enjoyed the largest Ka (5 × 106 M-1), competitively displaced weaker π-acceptors from the MOC18+ cavity, and generated the highest electrical conductivity (2.1 × 10-6 S/m) among the πA@MOC18+ inclusion complexes. This work demonstrates a unique through-space charge transport capability of πA@MOC18+ inclusion complexes featuring supramolecular π-D/A/D triads, which generated tunable electrical conductivity, which is a rare but much coveted electronic property of such supramolecular assemblies that could further expand their utility in future technologies.

An In-Depth Analysis of Variation in Characteristic Performance of OLED with Respect to Position of Charge Generation Layer

In this paper, a high performance blue organic light emitting diode having a charge generation layer (CGL) is proposed and compared with the other five CGL and non-CGL based devices. The utilized CGL layer in the different structure consists of two materials; HAT-CN (hexaazatriphenylene-hexacarbonitrile) and TAPC (1,1-bis[(di-4-tolyamino)phenyl)]cyclohexane,) for electrons and holes generation, correspondingly. In the proposed novel structure, the CGL layer is incorporated outside of the emissive layer (EML) which significantly enhances the device performance in terms of current and luminescence. The device exhibits luminescence and current values as 3636.3 cd m−2 and 0.44 A, respectively. Furthermore, this paper represents in-depth internal analysis of the six devices (D1-D6). This analysis is provided by drawing horizontal and vertical cutlines inside the devices. The proposed device is analysed and compared with other mentioned devices in terms of several parameters such as Langevin recombination rate, electron concentration, hole concentration, band energy, total current density, electron affinity, hole QFL (quasi-Fermi level), conduction current density, potential distribution and electron/hole mobility. In comparison with D1, D2, D3, D4 and D5, the current of the proposed device (D6) is about 16.9, 2.2, 1.7, 3 and 1.6 times improved, correspondingly. Moreover, structural analysis is also included to understand the performance of the devices more precisely.

Application of Thermal Response Measurements to Investigate Enhanced Water Adsorption Kinetics in Ball-Milled C2 N-Type Materials.

Sorption-based water capture is an attractive solution to provide potable water in arid regions. Heteroatom-decorated microporous carbons with hydrophilic character are promising candidates for water adsorption at low humidity, but the strong affinity between the polar carbon pore walls and water molecules can hinder the water transport within the narrow pore system. To reduce the limitations of mass transfer, C2 N-type carbon materials obtained from the thermal condensation of a molecular hexaazatriphenylene-hexacarbonitrile (HAT-CN) precursor were treated mechanochemically via ball milling. Scanning electron microscopy as well as static light scattering reveal that large pristine C2 N-type particles were split up to a smaller size after ball milling, thus increasing the pore accessibility which consequently leads to faster occupation of the water vapor adsorption sites. The major aim of this work is to demonstrate the applicability of thermal response measurements to track these enhanced kinetics of water adsorption. The adsorption rate constant of a C2 N material condensed at 700 °C remarkably increased from 0.026 s-1 to 0.036 s-1 upon ball milling, while maintaining remarkably high water vapor capacity. This work confirms the advantages of small particle sizes in ultramicroporous materials on their vapor adsorption kinetics. It is demonstrated that thermal response measurements are a valuable and time-saving method to investigate water adsorption kinetics, capacities, and cycling stability.

Synthesis of a Co-Nx type catalyst derived from the pyrolysis of a covalent triazine-based framework for oxygen reduction reaction

• A Co N C catalyst had been developed using an inexpensive and N -rich precursor. • The covalent triazine-based framework provided high density and evenly distributed M N C sites. • The HAT-CN-Co/C-800 catalyst showed the highest ORR activity close to Pt/C. The preparation of non-noble metal catalysts with performance in the oxygen reduction reaction (ORR) comparable or superior to platinum-based catalysts remains challenging. In the present study, hexaazatriphenylenehexacarbonitrile (HAT-CN), which is rich in both cyano groups and pyrazine units, was used as the precursor and then cyclotrimerized into a covalent triazine-based framework with a macrocyclic structure containing abundant complexation sites for transitional metal ions. Subsequently, a series of non-platinum Co N C type catalysts (HAT-CN-Co/C) were prepared, and then pyrolyzed at different temperatures (700 °C, 800 °C, and 900 °C). The pyrolysis treatment endowed the catalysts with activated Co-N x sites, large pore sizes and high specific surface areas, which can promote oxygen transfer and accelerate the ORR catalytic process. It is found that the catalyst (HAT-CN-Co/C-800) obtained from pyrolysis at 800 °C possessed the best ORR activity and followed the four- electrons transfer pathway; the onset potential of ORR was determined as 0.972 V vs reversible hydrogen electrode (RHE), very close to that of Pt/C (0.993 V vs RHE), and the half-wave potential (0.895 V vs RHE) was significantly higher than that of Pt/C (0.859 V vs RHE). Furthermore, the HAT-CN-Co/C-800 catalyst showed good durability (83.2 % current retention after 28000 s) and significant methanol tolerance with good application potential as a substitute for the platinum-based ORR catalyst in fuel cell.

Cobalt(II)‐Hexaazatriphenylene Hexacarbonitrile Coordination Compounds Based Cathode Materials with High Capacity and Long Cycle Stability

AbstractOrganic cathode materials are plagued by their low cycle stability and poor electronic conductivity, even though they have attracted increasing attention in the context of lithium‐ion batteries (LIBs). Herein, a coordination polymer cobalt‐hexaazatriphenylene hexacarbonitrile (Co(HAT‐CN)) is prepared via a facile solvothermal method, which is composed of the redox‐active HAT‐CN linker and the Co(II) ion center. The fabricated material shows excellent structural stability and high conductivity. Moreover, graphene oxide (GO) is introduced as a substrate, and in‐situ loading of Co(HAT‐CN) on its surface shows enhanced cycling stability. For Co(HAT‐CN)/GO, a high specific capacity of 204 mAh g–1 can be retained even after 200 cycles at a current density of 40 mA g–1 in a voltage window of 1.2–3.9 V. Ex situ and in situ analyses are applied to probe the reversibility of the pyrazine redox‐active center during the cycling process and the lithium storage process. Density functional theory calculations reveal that the high conductivity of Co(HAT‐CN) should be ascribed to the narrow LUMO‐HOMO gap (0.61 eV), and strong binding of lithiated molecules.

Enhanced Hole Injection Characteristics of a Top Emission Organic Light-Emitting Diode with Pure Aluminum Anode.

A top emitting organic light-emitting diode (OLED) device with pure aluminum (Al) anode for high-resolution microdisplays was proposed and fabricated. The low work function of the Al anode, even with a native oxide formed on the Al anode surface, increases the energy barrier of the interface between the anode and hole injection layer, and has poor hole-injection properties, which causes the low efficiency of the device. To enhance the hole-injection characteristics of the Al anode, we applied hexaazatriphenylene hexacarbonitrile (HATCN) as the hole-injection layer material. The proposed OLED device with a pure Al anode and native oxide on the anode surface improved efficiency by up to 35 cd/A at 1000 nit, which is 78% of the level of normal OLEDs with indium tin oxide (ITO) anode.

Understanding Structure–Property Relationships under Experimental Conditions for the Optimization of Lithium‐Ion Capacitor Anodes based on All‐Carbon‐Composite Materials

The nanoscale combination of a conductive carbon and a carbon‐based material with abundant heteroatoms for battery electrodes is a method to overcome the limitation that the latter has high affinity to alkali metal ions but low electronic conductivity. The synthetic protocol and the individual ratios and structures are important aspects influencing the properties of such multifunctional compounds. Their interplay is, herein, investigated by infiltration of a porous ZnO‐templated carbon (ZTC) with nitrogen‐rich carbon obtained by condensation of hexaazatriphenylene‐hexacarbonitrile (HAT‐CN) at 550–1000 °C. The density of lithiophilic sites can be controlled by HAT‐CN content and condensation temperature. Lithium storage properties are significantly improved in comparison with those of the individual compounds and their physical mixtures. Depending on the uniformity of the formed composite, loading ratio and condensation temperature have different influence. Most stable operation at high capacity per used monomer is achieved with a slowly dried composite with an HAT‐CN:ZTC mass ratio of 4:1, condensed at 550 °C, providing more than 400 mAh g−1 discharge capacity at 0.1 A g−1 and a capacity retention of 72% after 100 cycles of operation at 0.5 A g−1 due to the homogeneity of the composite and high content of lithiophilic sites.

Understanding the Charge Storage Mechanism to Achieve High Capacity and Fast Ion Storage in Sodium‐Ion Capacitor Anodes by Using Electrospun Nitrogen‐Doped Carbon Fibers

AbstractMicroporous nitrogen‐rich carbon fibers (HAT‐CNFs) are produced by electrospinning a mixture of hexaazatriphenylene‐hexacarbonitrile (HAT‐CN) and polyvinylpyrrolidone and subsequent thermal condensation. Bonding motives, electronic structure, content of nitrogen heteroatoms, porosity, and degree of carbon stacking can be controlled by the condensation temperature due to the use of the HAT‐CN with predefined nitrogen binding motives. The HAT‐CNFs show remarkable reversible capacities (395 mAh g−1 at 0.1 A g−1) and rate capabilities (106 mAh g−1 at 10 A g−1) as an anode material for sodium storage, resulting from the abundant heteroatoms, enhanced electrical conductivity, and rapid charge carrier transport in the nanoporous structure of the 1D fibers. HAT‐CNFs also serve as a series of model compounds for the investigation of the contribution of sodium storage by intercalation and reversible binding on nitrogen sites at different rates. There is an increasing contribution of intercalation to the charge storage with increasing condensation temperature which becomes less active at high rates. A hybrid sodium‐ion capacitor full cell combining HAT‐CNF as the anode and salt‐templated porous carbon as the cathode provides remarkable performance in the voltage range of 0.5–4.0 V (95 Wh kg−1 at 0.19 kW kg−1 and 18 Wh kg−1 at 13 kW kg−1).

High-Performance Organic Light-Emitting Diode with Substitutionally Boron-Doped Graphene Anode.

The hole-injection barrier between the anode and the hole-injection layer (HIL) is of critical importance to determine the device performance of organic light-emitting diodes (OLEDs). Here, we report on a record-high external quantum efficiency (EQE) (24.6% in green phosphorescence) of OLEDs fabricated on both rigid and flexible substrates, with the performance enhanced by the use of nearly defect-free and high-mobility boron-doped graphene as an effective anode and hexaazatriphenylene hexacarbonitrile as a new type of HIL. This new structure outperforms the existing graphene-based OLEDs, in which MoO3, AuCl3, or bis(trifluoromethanesulfonyl)amide are typically used as a doping source for the p-type graphene. The improvement of the OLED performance is attributed mainly to the appreciable increase of the hole conductivity in the nearly defect-free boron-doped monolayer graphene, along with the high work function achieved by the use of a newly developed hydrocarbon precursor containing boron in the graphene growth by chemical vapor deposition.

Energy level alignment at the interface of NPB/HAT-CN/graphene for flexible organic light-emitting diodes

Graphene is highly promising as an electrode for flexible optoelectronic devices due to its excellent conductivity and transparency. However, it is necessary to tailor its work function with a charge injection layer in order to obtain favorable energy level alignment for efficient charge injection. An adequate charge injection layer can only be chosen with the understanding of the interfacial electronic structure between a charge transport layer and an electrode. In this study, we investigated the energy level alignment of N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB)/hexaazatriphenylene hexacarbonitrile (HAT-CN)/graphene using in situ ultraviolet and X-ray photoelectron spectroscopy measurements. The effective work function of graphene was significantly increased by 0.94eV by the HAT-CN hole injection layer (HIL) due to the interface dipole formation. In addition, the charge generation barrier (CGB) between NPB and HAT-CN, which plays a decisive role in charge injection efficiency with a charge generation HIL, was measured to be 0.66eV. This CGB on graphene is the same as the CGBs on other electrodes, and smaller than that of the widely-used MoO3 HIL. Therefore, HAT-CN could be a promising HIL for efficient flexible organic light-emitting diodes with a graphene anode.

Impacts of Molecular Orientation on the Hole Injection Barrier Reduction: CuPc/HAT-CN/Graphene

The molecular orientation affected by the interaction between a substrate and deposited molecules plays an important role in device performance. It is known that the molecular orientation influences not only the charge transport property but also its electronic structure. Therefore, the combined study of morphology and electronic structure is of high importance for device application. As a transparent electrode, graphene has many promising advantages. However, graphene itself does not have an adequate work function for either an anode or a cathode, and thus the insertion of a charge injection layer is necessary for it to be used as an electrode. In this study, the hole injection barrier (HIB) reduction was investigated at the interface of copper phthalocyanine (CuPc)/graphene with the insertion of a hexaazatriphenylene hexacarbonitrile (HAT-CN) layer between them. The insertion of the HAT-CN layer roughens the originally flat graphene surface and it weakens the π-interaction between CuPc and of graphene. ...

A surface modification layer capable of tolerating substrate contamination on transparent electrodes of organic electronic devices

An organic molecule, hexaazatriphenylene hexacarbonitrile (HAT-CN), is found that it can be used not only as a hole-injecting material but also a surface modification material to clean contaminated substrate electrodes for the fabrication of organic electronic devices. As an example, HAT-CN can modify or “clean” indium-tin-oxide (ITO) anode surface in organic light-emitting diodes (OLEDs). Negative effect from ITO surface contamination on the electroluminescence performance of OLEDs can be dramatically reduced with this modification layer. As a result, the OLEDs with the same device architecture but with different ITO surface conditions, even with intentional contamination, can all exhibit substantially identical and superior electroluminescence performance. The surface modification function of this material is feasibly useful for the real fabrications of OLEDs as well as for advanced research on other organic electronic devices.

Initial stages of organic film growth characterized by thermal desorption spectroscopy

In the wake of the increasing importance of organic electronics, a more in-depth understanding of the early stages of organic film growth is indispensable. In this review a survey of several rod-like and plate-like organic molecules (p-quaterphenyl, p-sexiphenyl, hexaazatriphenylene–hexacarbonitrile (HATCN), rubicene, indigo) deposited on various application relevant substrates (gold, silver, mica, silicon dioxide) is given. The focus is particularly put on the application of thermal desorption spectroscopy to shed light on the kinetics and energetics of the molecule–substrate interaction. While each adsorption system reveals a manifold of features that are specific for the individual system, one can draw some general statements on the early stages of organic film formation from the available datasets. Among the important issues in this context is the formation of wetting layers and the dewetting as a function of the substrate surface conditions, organic film thickness and temperature.

HATCN-based charge recombination layers as effective interconnectors for tandem organic solar cells.

A comprehensive understanding of the energy-level alignment at the organic heterojunction interfaces is of paramount importance to optimize the performance of organic solar cells (OSCs). Here, the detailed electronic structures of organic interconnectors, consisting of cesium fluoride-doped 4,7-diphenyl-1,10-phenanthroline and hexaazatriphenylene-hexacarbonitrile (HATCN), have been investigated via in situ photoemission spectroscopy, and their impact on the charge recombination process in tandem OSCs has been identified. The experimental determination shows that the HATCN interlayer plays a significant role in the interface energetics with a dramatic decrease in the reverse built-in potential for electrons and holes from stacked subcells, which is beneficial to the charge recombination between HATCN and the adjacent layer. In accordance with the energy-level alignments, the open-circuit voltage of tandem OSC incorporating a HATCN-based interconnector is almost 2 times that of a single-cell OSC, revealing the effectiveness of the HATCN-based interconnectors in tandem organic devices.

Tuning the Work Function of Graphene-on-Quartz with a High Weight Molecular Acceptor

Ultraviolet and X-ray photoelectron spectroscopies in combination with density functional theory (DFT) calculations were used to study the change in the work function (Φ) of graphene, supported by quartz, as induced by adsorption of hexaazatriphenylene–hexacarbonitrile (HATCN). Near edge X-ray absorption fine structure spectroscopy (NEXAFS) and DFT modeling show that a molecular-density-dependent reorientation of HATCN from a planar to a vertically inclined adsorption geometry occurs upon increasing surface coverage. This, in conjunction with the orientation-dependent magnitude of the interface dipole, allows one to explain the evolution of graphene Φ from 4.5 eV up to 5.7 eV, rendering the molecularly modified graphene-on-quartz a highly suitable hole injection electrode.

Hole injection enhancement of a single-walled carbon nanotube anode using an organic charge-generation layer

We demonstrate significant hole injection enhancement of single-walled carbon nanotube (SWCNT) anodes in flexible organic light-emitting devices (OLEDs) by the insertion of a strong electron-accepting organic charge-generation layer (CGL), hexaazatriphenylene hexacarbonitrile (HAT–CN). To clarify the origin of hole injection improvement, we investigated interfacial electronic structures using in situ ultraviolet photoelectron spectroscopy, inverse photoelectron spectroscopy, theoretical calculations, and electrical measurements. The HAT–CN layer significantly increased the work function of SWCNT anodes and acted as an efficient CGL due to its deep-lying lowest unoccupied molecular orbital level, which arises from the strong electron-accepting characteristics of the carbonitrile endgroups. We compared the energy level alignment at the interface of the N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) hole transport layer/HAT–CN/SWCNTs with that of NPB/SWCNTs, and found that the highest occupied molecular orbital level of the NPB changed from 1.20 to 0.40eV with insertion of the HAT–CN layer. As a result, flexible OLEDs with the HAT–CN layer showed an order of magnitude larger current density and luminance than those without the HAT–CN layer.

Work function increase of transparent conductive electrodes by solution processed electron acceptor molecular monolayers

We show how the work function of transparent conductive oxide surfaces can be increased by more than 1 eV by solution-depositing strong electron acceptor monolayers comprising tetrafluoro-tetracyanoquinodimethane (F4TCNQ) or hexaazatriphenylene-hexacarbonitrile (HATCN). The effects of ambient atmosphere on the work function are investigated by comparing Kelvin probe measurements in air and ultraviolet photoelectron spectroscopy in ultrahigh vacuum. In this way, important technological issues related to the influence of ambient moisture on electrode properties are elucidated.

Linear and Hexagonal Porous Structures of an Organic Charge Acceptor Hexaaza-triphenylene-hexacarbonitrile on Au(111) with CN···CN Dipolar Interactions

Knowledge of molecular structures of emerging charge acceptors, such as hexaaza-triphenylene-hexacarbonitrile (HATCN), on metal surfaces is essential for their optoelectronic device applications. Here, we studied the two-dimensional molecular ordering of HATCN at submonolayer coverages on Au(111) using scanning tunneling microscopy (STM). Linear and hexagonal porous structures were observed at atomic steps and terraces, respectively, and our density functional theory calculations revealed that the structures were stabilized with CN···CN dipolar interactions. The hexagonal porous structures possess chirality, and they form only small (<1000 nm2) phase-separated chiral domains that easily change their structures in subsequent STM images at 80 K, which explains the no electron diffraction pattern reported previously.