High Hole Drift Mobility Research Articles

Differently substituted benzothiadiazoles as charge-transporting emitters for fluorescent organic light-emitting diodes

Carbazolyl- and 1,2,3,4-tetrahydrocarbazolyl-substituted benzothiadiazoles were prepared by Pd-catalyzed Buchwald-Hartwig and Heck reactions. Photophysical, electrochemical, thermal, charge-transporting properties, and performance in organic light emitting diodes (OLEDs) of the derivatives with donor-π-acceptor-π-donor and donor-acceptor-donor structures are discussed. Photo- and electroluminescent properties of the studied compounds of carbazole and benzothiadiazole are very sensitive to their molecular structures. Their glass transition temperatures range from 145 to 191 °C. Investigation of photophysical properties revealed importance of intramolecular twisting on excited state deactivation. Emission of dilute solutions of the compounds in nonpolar solvents appears in the orange region with fluorescence quantum yields up to 0.6.4,7-(Di (1,2,3,4-tetrahydro)carbazolyl)-[2,1,3]-benzothiadiazole demonstrates phosphorescence and delayed fluorescence at room temperature. Solid-state ionization potentials of the materials range from 5.64 to 5.82 eV. The layer of 4,7-(di (tert-butyl)carbazolyl)-[2,1,3]-benzothiadiazole shows high hole drift mobility of 1.7 × 10−3 cm2/V·s at an electric field of 5.3 × 105 V/cm and relatively high electron drift mobility of 5.7 × 10−5 cm2/V·s at an electric field of 5.8 × 105 V/cm. Red OLEDs based of singlet emission with maximum external quantum efficiency values of 1.3 and 0.13% were achieved using new emitters. Much better electroluminescent performance was observed for the compound having donor-acceptor-donor structure relative to the compound with donor-π-acceptor-π-donor structure.

Naphthyl substituted triphenylamine derivatives as hole transporting materials for efficient red PhOLEDs

Naphthyl substituted triphenylamine and its derivatives with bromine atoms were synthesized and investigated. The respective glass transition temperatures of the materials were estimated to be in a range 65–137 °C, which can provide morphologically-stable amorphous films for applications in organic light emitting diodes. The compounds possess adequate ionization potentials (5.5–5.75 eV), high hole drift mobilities (>10−3 cm2/V·s) and suitable triplet energies (∼2.4 eV), which make them suitable hole transporting materials for use in red phosphorescent organic light-emitting diodes. A superior peak efficiency of 17.9% (31.4 cd/A and 26.9 lm/W) was achieved in a device having hole transporting layer of tris[4-(1-naphthyl)phenyl]amine. Furthermore, the device gave efficiencies of 17.7% and 16.6% recorded at luminance levels of 102 and 103 cd/m2. The efficiency drop from the maximum to the value recorded at the luminance of 103 cd/m2 for the device was only 7%.

9,9′-bis(2,2-diphenylvinyl)[3,3′]bicarbazole as low cost efficient hole transporting material for application in red PhOLEDs

Low-cost bicarbazole-based hole transporting derivative with diphenylvinyl substitutions was synthesized by simple procedure and characterized. The respective glass transition temperature of the material was estimated to be 81 °C, which can provide morphologically-stable amorphous films for applications in organic light emitting diodes. The compound possesses an adequate ionization potential, suitable triplet energy and high hole drift mobility of 5.54 eV, 2,61 eV and of 2 × 10−3 cm2/V·s, respectively, which make it a suitable hole transporting material for use in red phosphorescent organic light-emitting diodes. The respective peak efficiency of the red device with the p-type dopant was recorded at 8.3% (5.2 cd/A and 3.3 lm/W) and at 7.8% (4.9 cd/A and 1.9 lm/W) for 100 cd/m [2] brightness, demonstrating high potential of the material for applications in light emitting diodes. The characteristics indicated that device with the bicarbazole-based compound exhibited better performance than those of widely used 1,1-bis [(di-4-tolylamino)phenyl]cyclohexane (TAPC) -based device.

Very high hole drift mobility in neat and doped molecular thin films for normal and inverted perovskite solar cells

Hole transporting layers (HTLs) have critical roles in the performance of perovskite solar cells. In this study, films of the vacuum-deposited small molecule of Tris[4-(5-phenylthiophene-2-yl)phenyl]amine (TPTPA) are demonstrated as efficient HTL materials for perovskite solar cells. The horizontal molecular stacking of the TPTPA neat film leads to the exceptionally high hole drift mobility of 7 × 10−3cm2V−1s−1, among the highest values observed in the organic molecular neat films. By doping with MoO3, a clear charge transfer state is formed and the hole mobility further increases to 3.6 × 10−2cm2V−1s−1. Both normal- and inverted-structured perovskite solar cells utilizing these HTLs are prepared and optimized; they show high power conversion efficiencies of 17–18%.

Synthesis and Investigation of the V-shaped Tröger's Base Derivatives as Hole-transporting Materials.

V-shaped Tröger's base core has been investigated as a central linking unit in the synthesis of new charge-transporting materials for optoelectronic applications. The studied molecules have been synthesized in two steps from relatively inexpensive starting materials, and demonstrate high glass transition temperatures, good stability of the amorphous state, and comparatively high hole drift mobility (up to 0.011 cm(2) V(-1) s(-1) ).

Impact of non-symmetric 2,9,10-aryl substitution on charge transport and optical properties of anthracene derivatives

A new methodology for the synthesis of non-symmetric 2,9,10-arylanthracenes is proposed. The anthracenes were intentionally decorated with non-symmetric aryls to improve charge transport properties. The impact of non-symmetric aryl substituents on optical and electrical properties was thoroughly studied. Non-symmetric 9,10-aryl substituents ensured blue emission in the range of 422–436 nm and fluorescence quantum efficiency of ca. 0.45, while the type of substituents had a minor impact on excited state deactivation due to their twisted configuration. Optical properties of the compounds obtained in dilute solution and in a rigid polymer matrix revealed the dominating non-radiative decay mechanism to be due to the intersystem crossing (ISC), which was mainly governed by 2-phenyl substitution. Favourable alignment of the singlet and triplet energy levels for efficient ISC was confirmed by density functional theory calculations. Some of the non-symmetrically substituted anthracene derivatives showed very high hole drift mobilities reaching 10−2 cm2/Vs in solution-processed neat films.

1,3-Bisdiphenylethenyl-substituted Carbazolyl Derivatives as Charge Transporting Materials

Synthesis of 1,3-diphenylethenylcarbazolyl-based charge transporting materials involving electron donating hydrazone moieties and an electron withdrawing 1,3-indandione moiety is reported. The obtained materials were examined by various techniques, including differential scanning calorimetry, UV-Vis spectroscopy, xerographic time of flight technique and the electron photoemission in air method. Photoemission spectra of the amorphous films of the investigated compounds showed ionization potentials of 5.54–5.90 eV. The hole drift mobility was measured by the xerographic time of flight technique. The highest hole drift mobility, exceeding 10−5 cm2/V·s at 6.4 × 105 V/cm electric field, was observed for the 1,3-diphenylethenylcarbazolyl derivative molecularly doped with a N,N-diphenylhydrazone moiety in the polymeric host bisphenol-Z polycarbonate (PC-Z).

Performance of blue fluorescence and red phosphorescent organic light‐emitting diodes using a molecular material with high hole drift mobility

AbstractThis study focuses on the carrier balance factor and transient characteristics of organic light‐emitting diodes (OLEDs) utilizing tris[4‐(5‐phenylthiophen‐2‐yl)phenyl] amine (TPTPA) as a blue emissive material or a host material of a red phosphorescent dye, which exhibits the highest level of hole drift mobility (µ = 1.0×10‐2 cm2V‐1s‐1) among those reported for organic disordered systems. We investigated the doping effect of a red phos‐phorescent material in the TPTPA. The peak wavelengths and the shape of the electroluminescent (EL) spectra agree with those of the photoluminescent spectra, which indicate that the EL originates from the excited state of the TPTPA and dopant. The maximum luminance of approximately 11,000 and 2,000 cd/m2 were achieved for devices without and with dopant. While TPTPA device achieved good carrier balance, the hole current was decreased by doping a red phosphorescent material. Compared with the short response times of TPTPA device, relatively long response times of doped device was observed owing to phosphorescent recombination lifetime of a dopant. The TPTPA device exhibited the relatively high light outcoupling efficiency of approximately 34% (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis of Triphenylamine Copolymers and Effect of Their Chemical Structures on Physical Properties

A series of charge transporting triphenylamine (TPA) polymers containing 2,1,3-benzothiadiazole (BTH) and/or 3,4-ethylenedioxythiophene (EDOT) unit(s) in the backbone were synthesized via C–N coupling polymerization using a palladium catalyst system. The preparation of the diblock copolymers based on the TPA-polymers was achieved by introducing poly(ethylene oxide) (PEO) at the terminal. Furthermore, the block copolymers selectively functionalized by BTH at the junction point were also prepared. In order to investigate the structural and morphological effect on physical properties, the optical and electrical properties were measured and compared among the homopolymers, random copolymers, and block copolymers. The photoluminescent (PL) spectra of TPA-polymers containing BTH unit were tunable from blue to red-violet color by the amount of BTH unit. The EDOT-containing polymers showed high hole drift mobility up to 1 × 10–3 cm2 V–1 s–1. On the other hand, the mobility of the BTH-containing polymers was affected by the position of the BTH unit in the polymer structure. The polymers with BTH unit randomly involved in the backbone showed low mobility in the order of 10–6–10–5, whereas no decrease in the mobility was observed for the polymers modified by BTH unit at the junction point.

Performance of Organic Light-Emitting Diodes Using an Emissive Material with High Hole Drift Mobility

This study focuses on the performance of organic light-emitting diodes (OLEDs) using an emissive material with high hole drift mobility, tris[4-(5-phenylthiophen- 2-yl)]amine (TPTPA), which exhibits the highest level of hole drift mobility (1.0 × 10−2 cm2 V−1 s−1) among those reported for organic disordered systems. Clear blue emission was observed from TPTPA which was used as the hole transporting and emissive layer in the OLEDs. The maximum luminance of 1.2 × 104 cd/m2, and the maximum current efficiency of 3.9 cd/A were achieved. The short response times of electroluminescence (ca. 10 ns) were achieved under the application of rectangular-shaped voltages.

One small step in synthesis, a big leap in charge mobility: diphenylethenyl substituted triphenylamines

Star-shaped charge transporting materials with a triphenylamine core and a varying number of diphenylethenyl sidearms, obtained using a one step synthesis procedure from commercially available and relatively inexpensive starting materials and possessing comparatively high hole drift mobility (up to 0.017 cm(2) V(-1) s(-1)), are reported.

High‐Performance Organic Photovoltaic Devices Using a New Amorphous Molecular Material with High Hole Drift Mobility, Tris[4‐(5‐phenylthiophen‐2‐yl)phenyl]amine

AbstractA new amorphous molecular material, tris[4‐(5‐phenylthiophen‐2‐yl)phenyl]amine (TPTPA), is synthesized and characterized. TPTPA forms a stable amorphous glass with a glass‐transition temperature of 83 °C when the melt sample is cooled. It also forms amorphous thin films by a thermal deposition technique. TPTPA exhibits a hole drift mobility of 1.0 × 10−2 cm2 V−1 s−1 at an electric field of 1.0 × 105 V cm−1 and at 293 K, as determined by the time‐of‐flight method, which is of the highest level among those of amorphous molecular materials. pn‐Heterojunction organic photovoltaic devices (OPVs) using TPTPA as an electron donor and C60 or C70 as an electron acceptor exhibit high performance with fill factors of 0.66∼0.71 and power conversion efficiencies of 1.7∼2.2% under air‐mass (AM) 1.5G illumination at an intensity of 100 mW cm−2, which are of the highest level ever reported for OPVs using amorphous molecular materials.

High performance organic photovoltaic devices using amorphous molecular materials with high charge-carrier drift mobilities

p n -Heterojunction organic photovoltaic devices (OPVs) using amorphous molecular materials with high hole drift mobilities of 10−2 cm2 V−1 s−1, tris[4-(2-thienyl)phenyl]amine and tris[4-(5-phenylthiophen-2-yl)phenyl]amine, as electron donors and fullerene as an electron acceptor were fabricated. In spite of the use of amorphous materials instead of crystalline materials, the devices exhibited high performance with fill factors of 0.62–0.71 and power conversion efficiencies of 1.5%–1.7% under air-mass 1.5 G illumination at an intensity of 100 mW cm−2.

A thermally cured 9,9-diarylfluorene-based triaryldiamine polymer displaying high hole mobility and remarkable ambient stability

We have synthesized and characterized a novel thermally polymerizable triaryldiamine monomer (VB-FNPD) possessing a styrene-functionalized 9,9-diarylfluorene core and have used time-of-flight transient photocurrent techniques to investigate the hole transport properties of its solution-processed and subsequently thermally cured (170 °C) polymer films. This novel polymeric material exhibits non-dispersive hole transport behavior with a high hole drift mobility (up to 10−4 cm2V−1 s−1). The film displayed remarkable ambient stability, even when exposed to air for one month. We tested the thermally generated polymer film as a hole transport material in organic light-emitting diodes incorporating tris(8-hydroxyquinolate) aluminium (Alq3) as the emission and electron transport layer. The device exhibited a maximum external quantum efficiency (ηex) of 1.4%, significantly better than that of the device prepared using the corresponding model compound VB-model (ηex = 1.1%).

Carbazole-based bis(enamines) as effective charge-transporting amorphous molecular materials

A series of carbazole-based bis(enamines) as glass-forming hole transport materials has been synthesized and characterized. The amorphous films of the reported compounds demonstrate extraordinarily high hole-drift mobilities reaching 5 × 10 −2 cm 2/V s at high electric fields. To our knowledge this is one of the highest values observed to date for amorphous molecular p-type semiconductors. The reported compounds constitute materials with high thermal stability with five percent weight loss temperatures exceeding 370 °C as characterised by thermogravimetric analysis. They form glasses with the glass transition temperatures ranging from 83 to 126 °C as established by differential scanning calorimetry. Photoelectric properties of the materials were examined by electron photoemission and time of flight technique. The electron photoemission spectra of the layers revealed the ionization potentials as low as 4.98–5.15 eV.

Novel Charge Transporting Materials Containing Phenyl-1,2,3,4-Tetrahydroquinoline Moieties

New synthesized monohydrazone and dihydrazone containing 1-phenyl-1,2,3,4-tetrahydroquinoline moiety were investigated. The materials were examined by various techniques including differential scanning calorimetry (DSC), UV spectrometry, electron photoemission and xerographic time of flight (XTOF) techniques. The highest hole drift mobility 10−5 cm2V−1s−1 at an electric field of 106 Vcm−1 was observed for the dihydrazone.

Novel dihydrazone based polymers for electrophotography

The novel family of hole-transporting polymers containing hydrazone moieties is reported. The polymers were prepared in polyaddition reaction of dihydrazone-containing diepoxides with bifunctional nucleophilic linking agents in the presence of catalyst triethylamine. Obtained polymers were found to constitute novel polymeric hole transporting materials characterized by differential scanning calorimetry and time of flight method. The highest hole drift mobility in the newly synthesized polymers exceed 10 −5 cm 2 V −1 s −1 at an electric field of 10 6 V cm −1.

Highly transparent microcrystalline silicon carbide grown with hot wire chemical vapor deposition as window layers in n-i-p microcrystalline silicon solar cells

Microcrystalline silicon carbide (μc-SiC) films were prepared using hot wire chemical vapor deposition at low substrate temperature. The μc-SiC films were employed as window layers in microcrystalline silicon (μc-Si:H) n-i-p solar cells. Quantum efficiency (QE) and short circuit current density (JSC) in these n-side illuminated n-i-p cells were significantly higher than in standard p-i-n cells. A high QE current density of 26.7mA∕cm2 was achieved in an absorber layer thickness of 2μm. The enhanced JSC was attributed to the wide band gap of the μc-SiC layer and a sufficiently high hole drift mobility in μc-Si:H absorber layer.

Novel hydrazone moieties containing polymers for optoelectronics

The novel family of hole transporting polymers containing hydrazone moieties is reported. The polymers were prepared in polyaddition reaction of hydrazone-containing diepoxydes with 2,5-dimercapto-1,3,4-thiadiazole in the presence of catalyst triethylamine (TEA). Obtained polymers were found to constitute novel polymeric hole transporting materials (TM) characterized by differential scanning calorimetry (DSC) and time of flight method. The highest hole-drift mobility in the newly synthesized polymers exceed 10 −5 cm 2 V −1 s −1 at an electric field of 10 6 V cm −1 was observed in the TM with triphenylamine moieties. The electron photoemission spectra of the obtained polymers have been recorded and the ionization potentials of 5.24–5.33 eV have been determined.

Novel hydrazone based polymers as hole transporting materials

The novel family of hole transporting polymers containing hydrazone moieties is reported. The polymers were prepared in polyaddition reaction of hydrazone-containing diepoxydes with 4,4′-thiobisbenzenethiol in the presence of catalyst triethylamine (TEA). Obtained polymers were found to constitute novel polymeric hole transporting materials (TM) characterized by differential scanning calorimetry and time of flight method. The highest hole drift mobility in the newly synthesized polymers exceed 10−4cm2V−1s−1 at an electric field of 106Vcm−1 was observed in the TM with triphenylamine moieties.