Hole-transporting Polymers Research Articles

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.

Synthesis and characterization of novel photoconducting carbazole derivatives in main-chain polymers for photorefractive applications

We have prepared hole-transporting polymers that have carbazole and 3,3′-dicarbazole in the main chain by polycondensation based on Fridel–Craft reaction via cations generated by proton of p-toluene sulfonic acid catalyst. In the device, they display high diffraction efficiency at low external electric field. The DiCz composite had a high diffraction efficiency of 82.4% at 52 V/μm and a photorefractive response time constant of 1.18 s at an electric field of 50 V/μm and a writing intensity of 60 mW/cm 2. The samples have excellent properties with respect to optical quality and shelf-lifetime.

Novel Photo-Cross-Linkable Hole-Transporting Polymers: Synthesis, Characterization, and Application in Organic Light Emitting Diodes

Novel polymeric hole-transporters P1 through P4 were synthesized based on triarylamine units in the backbone with pendant oxetane groups which can be used for photo-cross-linking. These polymers were characterized by NMR spectroscopy, GPC, IR spectroscopy, and DSC. Their electrochemical properties were investigated by means of cyclic voltammetry. Multilayer organic light emitting devices were fabricated layer by layer using inexpensive solution based methods like spin-coating followed by a cross-linking step. UV spectroscopy was used to prove that the spin-coated layers are totally insoluble after the cross-linking process. The hole-transport capabilities of the polymers were evaluated in hole-only devices and finally multilayer OLEDs were fabricated to test the performance of the synthesized compounds.

Comparison of blended versus layered structures for poly(p-phenylene vinylene)-based polymer photovoltaics

We characterize and compare blended and bilayered heterojunctions of polymer photovoltaic devices using poly[oxa-1,4-phenylene-1,2-(1-cyano)-ethenylene-2,5-dioctyloxy-1,4-phenylene-1,2-(2-cyano)-ethenylene-1,4-phenylene] (CN-ether-PPV) and poly[2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-1,2-ethenylene] (M3EH-PPV) as electron- and hole-transporting polymers, respectively. We find that both blended and bilayered structures have substantially improved current densities (>3mA∕cm2) and power efficiencies (∼1% under white light) over neat films. Improved exciton dissociation at multiple interfaces and reduced recombination due to energy and charge transfers increases the charge-carrier collection in both types of heterojunction devices, but low electron mobilities in the polymers lead to low fill factors and reduced quantum efficiency (∼20%) that limit the power efficiency. Time-resolved photoluminescence reveals that for blended structures both the hole and electron-transporting polymers undergo efficient quenching with the exciton decay being dominated by the existence of two fast decay channels of 0.12 and 0.78ns that are assigned to interspecies charge transfer and account for the increased short-circuit current observed. For layers, these components are not as prevalent. This result indicates that greater exciton generation at the dissociating interface and more efficient charge collection in the thin layers is primarily responsible for the improved short-circuit current, a conclusion that is further supported by numerical simulations of the exciton generation rate and charge collection. We also report evidence for an intermediate exciplex state in both types of structures with the greatest yield for blends with 50wt% of CN-ether-PPV. Overall, the improved performance is due to different processes in the two structures; efficient bulk exciton quenching and charge transfer in blends and enhanced exciton generation and charge collection in layers. The optimization of each photovoltaic heterostructured device relies on this understanding of the mechanisms by which each material architecture achieves high power efficiencies.

Novel Families of Hole-Transporting Monomers and Polymers

Abstract The novel families of hole transporting monomers and polymers containing hydrazone moieties are reported. The polymers were prepared in polyaddition reaction of hydrazone-containing diepoxides with 4,4′-thiobisbenzenethiol. The hole drift mobilities in the newly synthesized polymers exceed 10−4 cm2 V−1s−1 and in the compositions of the monomers with polymeric binder exceed 10−6 cm2 V−1s−1 at an electric field of 106 V cm−1 as characterized by the xerographic time of flight technique.

Interface Engineering for Solid‐State Dye‐Sensitized Nanocrystalline Solar Cells: The Use of Ion‐Solvating Hole‐Transporting Polymers

AbstractThe control of interfacial charge transfer is central to the design of photovoltaic devices. This charge transfer is strongly dependent upon the local chemical environment at each interface. In this paper we report a methodology for the fabrication of a novel nanostructured multicomponent film, employing a dual‐function supramolecular organic semiconductor to allow molecular‐level control of the local chemical composition at a nanostructured inorganic/organic semiconductor heterojunction. The multicomponent film comprises a lithium ion doped dual‐functional hole‐transporting material (Li+–DFHTM), sandwiched between a dye‐sensitized nanocrystalline TiO2 film and a mono‐functional organic hole‐transporting material (MFHTM). The DFHTM consists of a conjugated organic semiconductor with ion supporting side chains, designed to allow both electronic and ionic charge transport properties. The Li+–DFHTM layers provide a new and versatile way to control the interface electrostatics, and consequently the charge transfer, at a nanostructured dye‐sensitized inorganic/organic semiconductor heterojunction.

Development of a new class of hole-transporting and emitting vinyl polymers and their application in organic electroluminescent devices

Abstract A new class of hole-transporting vinyl polymers, poly{4-vinyl-4 ′ -[bis(4 ′ - tert -butylbiphenyl-4-yl)amino]biphenyl} (PVBAB) and poly{4-vinyl-4 ′ -[ N , N -bis(9,9-dimethylfluoren-2-yl)amino]biphenyl} (PVFAB), and a new emitting vinyl polymer, poly(2-{4-[4-vinylphenyl(4-methylphenyl)amino]phenyl}-5-dimesitylborylthiophene) (PVPhAMB-1T), were designed and synthesized. These new vinyl polymers form smooth amorphous films with high glass-transition temperatures of ca. 200 °C. PVBAB and PVFAB possess electron-donating properties, and PVPhAMB-1T possesses bipolar character with both electron-donating and accepting properties, exhibiting strong fluorescence in solution and as films. Organic electroluminescent devices using PVBAB or PVFAB as a hole-transport layer and N , N ′ -dimethylquinacridone-doped tris(8-quinolinolato)aluminum as an emitting layer were thermally stable and exhibited very high performance. The use of PVPhAMB-1T as an emitting material also permitted the fabrication of a high-performance, green-emitting organic EL device.

Synthesis and characterization of new 4‐tolyldiphenylamine derivatives for hole transporting polymers

AbstractNew hole transport polymers have been synthesized by condensation polymerization of 4‐tolyldiphenylamine (TDPA) with various types of aldehyde. The reaction conditions have been investigated to yield polymers with high molecular weight. It is found that the molecular weight and yield of the TDPA–aldehyde polymers strongly depend on the electron donor–acceptor nature of the substituent on the aromatic ring of the aldehyde monomer. Structural characterization by 1H NMR spectroscopy shows that the addition condensation reaction occurs exclusively at the para position of TDPA. The electrochemical and optical properties of polymers have been investigated by cyclic voltammetry and UV–vis spectroscopy. Cyclic voltammograms of all polymers show well‐defined pairs of reduction and oxidation peaks, indicating that the polymers are electrochemically active. All polymers show low conductivities of magnitude 10−14 S cm−1. Differential scanning calori‐metry measurements reveal that TDPA–aldehyde polymers exhibit glass transitions in the range 170–230 °C. These polymers possess good solubility and the films show sufficient morphological stability.© 2001 Society of Chemical Industry

Crosslinkable hole-transporting polymers by palladium-catalyzed C—N-coupling reaction

Combination of spin-coating and crosslinking allows low-cost fabrication of large area displays with multiple layers by simple solution processing. For this purpose, a series of novel crosslinkable polymers containing hole-transporting triarylamine units in the main chain were synthesized via palladium-catalyzed C—N-coupling reaction. Additionally, they contain varying amounts of polymerizable oxetane groups as side chains. The polymers were photo-crosslinked to yield absolutely insoluble networks. Thin films were used as hole-transport layer in two-layer blue light-emitting diodes.

Crosslinkable hole-transporting polymers by palladium-catalyzed C—N-coupling reaction

Combination of spin-coating and crosslinking allows low-cost fabrication of large area displays with multiple layers by simple solution processing. For this purpose, a series of novel crosslinkable polymers containing hole-transporting triarylamine units in the main chain were synthesized via palladium-catalyzed C-N-coupling reaction. Additionally, the contain varying amounts of polymerizable oxetane groups as side chains. The polymers were photo-crosslinked to yield absolutely insoluble networks. Thin films were used as hole-transport layer in two-layer blue light-emitting diodes. Absorption spectrum of a films of 8c crosslinked on ITO and cured at 150°C before and after washing with THF. Crosslinking was carried out in bulk with 2 wt.-% of photoacid 4-(thio-phenoxyphenyl)dephenylsulfonium hexafluoroantimonate 18) by irradiation with UV light (>280nm) for 10 s

Organic Two-Layer Light-Emitting Diodes Based on High-Tg Hole-Transporting Polymers with Different Redox Potentials

A series of soluble arylamine-based hole-transporting polymers with glass transition temperatures in the range of 130−150 °C have been synthesized. The synthetic methodology allows facile substitution of the aryl groups on the amine with electron-withdrawing and electron-donating moieties, which permits tuning of the redox potential of the polymer. These polymers have been used as hole-transport layers (HTLs) in two-layer light-emitting diodes ITO/HTL/Alq/Mg [ITO = indium tin oxide, Alq = tris(8-quinolinato)aluminum]. The maximum external quantum efficiency of the device increases if the redox potential of the HTL is increased to facilitate reduction of the positive charge carriers at the HTL/Alq interface. A fluorinated hole-transport polymer with a relatively large redox potential (390 mV vs ferrocenium/ferrocene) yielded the device with the highest external quantum efficiency of 1.25% photons/e-. The device stability, however, follows the opposite trend. The device with the most electron-rich HTL exhibited the best performance after prolonged usage.

Light-Emitting and Hole-Transporting Polymers for LEDs

AbstractVarious copolymers of arylene vinylenes, having strong fluorescence, showed predominantly the emission in the multi-layer device using an electron-transporting material(ETM) such as tris(8-quinolinolato)aluminum(Alq3). The emission from Alq3 was suppressed due to the high hole-injection barrier from the copolymers to ETM in spite of low or no barriers of electron injection from ETM to the copolymers. We have successfully prepared highly hole-transporting polysilane having a triphenylamine group as a side chain(TPA-PS). The hole mobility as high as 10 cm3cm2/Vs is attributable to the intermolecular hopping process facilitated by the interaction between the polysilane backbone and the triphenylamine group. The polysilane is effectively used as a hole transporting material. The bilayer LED device consisting of TPA-PS and Akb3 showed high luminance (2000cd/m2) and high efficiency (4cd/A).