Organic Electronics 2010 Volume 11 №12

Elsevier. — 163 p. — ISSN: 1566-1199.«Organic Electronics» is a journal whose primary interdisciplinary focus is on materials and phenomena related to organic devices such as light emitting diodes, thin film transistors, photovoltaic cells, sensors, memories, etc.Papers suitable for publication in this journal cover such topics as photoconductive and electronic properties of organic materials, thin film structures and characterization in the context of organic devices, charge and exciton transport, organic electronic and optoelectronic devices.«Organic Electronics» provides the forum for applied, fundamental and interdisciplinary contributions spanning the wide range of electronic properties and applications of organic materials. A Letters section is included for rapid publication of short articles announcing significant and highly original results.1877-1885
Merve Sendur, Abidin Balan, Derya Baran, Baris Karabay, Levent Toppare. Combination of donor characters in a donor–acceptor–donor (DAD) type polymer containing benzothiadiazole as the acceptor unit
Abstract:
A benzothiadiazole bearing donor–acceptor–donor (D–A–D) type monomer (M₃) was synthesized using the combination of 3, 4-ethylenedioxythiophene (EDOT) and thiophene donor units to understand the effect of donor strength on the optoelectronic and electrochemical properties. The resulting monomer was polymerized electrochemically (P₃) and compared with its symmetrical thiophene (P₁) and EDOT (P₂) bearing homologues whether there exists a combination of the electrochemical and optical characteristics. Also, copolymer studies were performed with symmetrical thiophene (M₁) and EDOT (M₂) containing monomers in order to compare the results with P₃. Cyclic voltammetry (CV) and spectroelectrochemistry results revealed that P₃ is a low band gap polymer (1,18 eV) having both p-and n-type property which is superior to the copolymers synthesized using M₁ and M₂.1886-1890
Hirotake Kajii, Yutaka Ie, Masashi Nitani, Youhei Hirose, Yoshio Aso, Yutaka Ohmori. N-channel organic field-effect transistors containing carbonyl-bridged bithiazole derivative fabricated using polyfluorene derivatives as solution-processed buffer layers
Abstract:
The effects of adding solution-processed polyfluorene derivatives as buffer layers between the polymer insulator and active layer of n-channel organic field-effect transistors (OFETs) containing a carbonyl-bridged bithiazole derivative were investigated. The surface free energy was modified by the polyfluorene derivatives. A poly(9,9-dioctylfluorene) (F8) buffer layer, which has a hydrophobic nature, a low surface free energy, and consists almost entirely of a dispersion component, improved the growth morphology of the OFET active layer. An OFET with an F8 buffer layer exhibited n-channel characteristics, and an electron field-effect mobility of 0,025 cm² V^-1 s^-1.1891-1895
Dan-Dan Zhang, Jing Feng, Yu-Qing Zhong, Yue-Feng Liu, Hai Wang, Yu Jin, Yu Bai, Qi-Dai Chen, Hong-Bo Sun. Efficient top-emitting organic light-emitting devices using Fe3O4 modified
Ag anode
Abstract:
Highly efficient top-emitting organic light-emitting devices (TOLEDs) using a Fe₃O₄ modified Ag anode have been demonstrated. The tris-(8-hydroxyquinoline) aluminum-based TOLEDs exhibit a very low turn-on voltage of 2,5 V and a high current efficiency of 8,1 cd/A. The improved properties for the TOLEDs is mainly due to the enhanced hole injection by introducing the anodic buffer. The mechanism of this enhanced hole injection is studied by the X-ray and ultra-violet photoemission spectroscopy, which demonstrated that the dipole layer is formed at the anode/organic interface and the hole-injection barrier is therefore reduced after introducing the thin Fe₃O₄ film between the Ag anode and the
hole-transport layer.1896-1900
Smita Sarkar, Jason H. Culp, Jon T. Whyland, Margret Garvan, Veena Misra. Encapsulation of organic solar cells with ultrathin barrier layers deposited by ozone-based atomic layer deposition
Abstract:
Ultrathin Al₂O₃ layers, deposited using atomic layer deposition (ALD), have been utilized as the primary barrier layers for encapsulation of organic solar cells. This work shows that the encapsulation characteristics of a barrier layer can be accentuated by replacing H₂O with O₃ as the ALD oxidant. The Al₂O₃ layers deposited using O₃ offered superior device encapsulation compared to the films deposited using H₂O. The organic solar cell efficiency has also been studied as a function of Al₂O₃ thickness and effective encapsulation has been monitored for two different ALD temperatures.1901-1908
Chung-Chia Chen, Bo-Chao Huang, Ming-Shiang Lin, Yin-Jui Lu, Ting-Yi Cho, Chih-Hao Chang, Kun-Cheng Tien, Su-Hao Liu, Tung-Hui Ke, Chung-Chih Wu. Impedance spectroscopy and equivalent circuits of conductively doped organic hole-transport materials
Abstract:
In this work, the impedance spectroscopy was adopted to characterize conductively doped organic hole-transport layers. We performed comparative studies of the impedance spectroscopy of undoped and doped hole-transport materials, by both experiment and simulation approaches. The impedance spectroscopy of the non-doped hole-transport material can be well understood by simply adopting the conventional RC equivalent circuits and considering the dielectric response frequency-independent. For the conductively doped organic hole-transport materials, however, successful modeling of the impedance spectroscopy results need to take into account the more complicated situations: including the difference between the bulk region and the depletion region near the electrode, and dispersion (i.e. frequency dependence) in the dielectric response of the conductively doped transport layer. As such, it is found necessary to include the complex dielectric response and the non-conventional complex impedance element in the equivalent circuit to achieve tight matching of simulated results with experiment results over wide bias and frequency ranges.1909-1915
Shanshan Wang, Zuqiang Bian, Xinyuan Xia, Chunhui Huang. Heterojunction organic solar cells based on donor-п-acceptor small molecule layers with controlled interface morphology
Abstract:
Small molecules have a great potential in developing organic solar cells owing to their well-controlled structure and tunable electronic properties by functionalization. Here, we use a classical fluorescent dye with a D-п-A structure, 4-(dicyanomethylene)-2-methyl-6-(4-dimethyl-aminostyryl)-4H-pyran (DCM), as an efficient light absorption layer with sensitivity at wavelengths of 400–600 nm where the aromatic amine/C₆₀ cells have low absorbance. Combined with a p-type transporting layer of selected aromatic amines, the much improved layer and interface morphology yield solar cell power conversion efficiency up to 1,68% under AM 1,5 and 100 mWcm^-2 illumination. The morphology of active organic layers, their interface, and the influence on the cell performance have been systematically studied.1916-1919
Alexander Isphording, Manfred Pralle. Quantifying angular color stability of organic light-emitting diodes
Abstract:
We show the need for a quantity that describes the angular dependence of the chromaticity emitted from organic light-emitting diodes (OLEDs), present different quantities that may be suitable for describing this color stability and compare these quantities to ratings obtained from a perception test to determine which quantity correlates most strongly with the observer ratings.1920-1927
L. Reséndiz, M. Estrada, A. Cerdeira, B. Iñiguez, M.J. Deen. Effect of active layer thickness on the electrical characteristics of polymer thin film transistors
Abstract:
In this paper, we analyze the variation of the threshold voltage V_T and carrier mobility lfet with the active layer thickness of polymer thin film transistors (PTFTs). The value of V_T was observed to become more negative as the active layer thickness decrease, while mobility slightly increased. Simulations obtained for different active layer thickness were first validated with experimental data from measured devices with known active layer thickness. Then using the calibrated simulator, it was found that as the semiconductor thickness decreased, the charge per square units in the active layer changes, establishing the cause of both of these behaviors.1928-1934
Keke K. Zhang, Kejie Tan, Changji Zou, Magnus Wikberg, Laurie E. McNeil, Subodh G. Mhaisalkar, C. Kloc. Control of charge mobility in single-crystal rubrene through surface chemistry
Abstract:
The mobility of rubrene single-crystal field-effect transistors has been measured in the presence of hydrogen and oxygen gas. The mobility of as-grown crystals is ~10 cm²/V s but falls to 0,01 cm²/V s during reduction in a hydrogen environment, and returns to nearly its original value in oxygen. Several cycles of surface reduction and oxidation have been done, which indicates that the surface reactions are reversible and the mobility can be changed to any value between that of the oxidized surface (10 cm²/V s) and that of the reduced surface (0,01 cm²/V s). Fourier-transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectroscopy have been applied to examine the oxidized and reduced surface of the rubrene single crystal. FTIR, Raman and PL spectroscopies reveal differences between the rubrene surface and bulk depending on the state of surface oxidation. We conclude that high field-effect mobility in rubrene crystals is a result of surface doping by an oxidized layer on the crystal surface and not due to the intrinsic molecular and crystal structure of rubrene.1935-1941
К сожалению отсутствует/Unfortunately missing1942-1946
Xiaohong Chen, Jiaxiang Yang, Lim Yi Xuan Candy Haley, Jiong Lu, Furong Zhu, Kian Ping Loh. Towards high efficiency solution processable inverted bulk heterojunction polymer solar cells using modified indium tin oxide cathode
Abstract:
High efficiency inverted regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM)-based polymer solar cells (PSCs) using an indium tin oxide (ITO) cathode, modified with a solution-processed ionic liquid-functionalized carbon nanoparticles (ILCNs) layer, was demonstrated. ILCNs-modified ITO cathode has a very good thermal stability and a superior surface electronic property suited for application in polymer solar cells. A power conversion efficiency (PCE) of 3,2% was obtained for inverted PSCs measured under AM1,5G illumination of 100 mW/cm², which is comparable to PCE of a reference P3HT:PCBM-based solar cell having a conventional structure. There was almost no deterioration in the performance of inverted PSCs that were aged over a post-annealing temperature range from 100 to 200 °C. The work function of ILCNsmodified ITO cathode annealed at different temperatures was also measured using ultraviolet photoelectron spectroscopy. It was found that the work function of 4,4 eV, measured for a bare ITO electrode, decreased to 3,8 eV when it was modified with ILCNs, and was not dependent on the post-annealing temperature.1947-1953
Chia-Hsin Wang, Yung-Chiuan Cheng, Jing-Wen Su, Liang-Jen Fan, Peng-Yi Huang, Ming-Chou Chen, Yaw-Wen Yang. Origin of high field-effect mobility in solvent–vapor annealed anthradithiophene derivative
Abstract:
Solvent–vapor annealing was used to increase the field-effect mobility of soluble triethylsilylethynyl anthradithiophene spin-coated on organosilane-terminated silicon dioxide, yielding a high value of 1,2 cm² V^-1 s^-1. The cause of improvement was investigated by atomic force microscopy, X-ray diffraction, and near-edge X-ray absorption fine structure spectroscopy. Vapor annealing exerts little effect on the molecular tilt and the crystallinity normal to the surface, but improves the film morphology significantly, yielding larger grains with perhaps better in-plane crystallinity.1954-1959
Yafei Wang, Yu Liu, Xiaoshuang Li, Hongrui Qi, Meixiang Zhu, Lei Wang, Gangtie Lei, Qiliang Wei, Weiguo Zhu, Junbiao Peng, Yong Cao. Novel cyclometalated platinum (II) complex containing alkyl-trifluorene picolinic acid as emitter for single-layer white PLEDs
Abstract:
To explore the influence of molecular structure on formation excimers and obtain highefficiency white polymer light-emitting devices, two novel blue-emitting cyclometalated platinum (II) complexes of (dfppy)Pt(Tfl-pic) and (C₁₆dfppy)Pt(Tfl-pic) have been successfully synthesized and characterized, where dfppy is 2-(2,4-difluoro-phenyl)pyridine, C₁₆dfppy is 5-hexdecanyl-2-(2,4-difluorophenyl)pyridine and Tfl-pic is alkyltrifluorenecontaining picolinic acid derivative. Compare to (dfppy)Pt(pic), both of platinum (II) complexes exhibited high thermal stability, good solubility and excellent photoluminescent quantum efficiency (about 94% ± 10%) at room temperature. Deep blue emission at about 418 nm in dilute dichloromethane (10^-5 M) and red-shifted emission at about 619 nm in the neat film were observed under opto-excitation. Pure white light with a CIE coordinates (0,33, 0,33) at 10 V was obtained in the (dfppy)Pt(Tfl-pic)-doped devices and a red emission was obtained in the (C₁₆dfppy)Pt(Tfl-pic)-doped devices with the same device configuration using a blend of polyvinylcarbazole and 2-(4-biphenyl)-5-(4-tertbutylphenyl)-1,3,4-oxadiazole as a host matrix, respectively.1960-1965
Natalia A. Azarova, Jack W. Owen, Claire A. McLellan, Marsha A. Grimminger, Eric K. Chapman, John E. Anthony, Oana D. Jurchescu. Fabrication of organic thin-film transistors by spray-deposition for low-cost, large-area electronics
Abstract:
We report on high performance organic thin-film transistors fabricated by spray-deposition, an innovative coating technique for organic electronic devices. This method is simple and inexpensive, compatible with room-temperature processing and easily scalable from laboratory-based devices to large-area electronics. Our spray-deposited 2,8-difluoro-5,11-bis (triethylsilylethynyl) anthradithiophene transistors show very good homogeneity, with mobilities of 0:2 cm²=V s, and on/off ratios of 10⁷. This performance is comparable to that of our best spin-coated devices fabricated on the same substrate type, while offering additional advantages such as using 20 times less organic semiconductor and facilitating fast coating of large-areas.1966-1973
Musubu Ichikawa, Kenta Wakabayashi, Shuichi Hayashi, Norimasa Yokoyama, Toshiki Koyama, Yoshio Taniguchi. Bi- or ter-pyridine tris-substituted benzenes as electron-transporting materials for organic light-emitting devices
Abstract:
We demonstrated that 1,3,5-tris([2',2'']bipyridin-6'-yl)benzene (BpyB) and 1,3,5-tris([2',2'',6'',2''']terpyridin-6’-yl)benzene (TpyB) are good electron-transport (ET) layer materials for organic light-emitting devices (OLEDs). The new materials exhibit high electron mobilities of around 10^-4 cm² V^-1 s^-1, and OLEDs comprising the materials operate at lower voltage than the OLEDs with tris(8-hydroxyquinolinato) aluminum (Alq) as an ET material. The new materials are also useful for phosphorescent OLEDs in blue-, green-, and red-light-emitting devices, where they function as both electron-transporting and hole-blocking materials. Phosphorescent OLEDs with the new materials operate at lower voltage (while maintaining comparable external quantum efficiencies of electroluminescence) than does the corresponding reference device with bathocuproine/Alq as electron-transporting and hole-blocking layers.1974-1990
Mihai Irimia-Vladu, Pavel A. Troshin, Melanie Reisinger, Guenther Schwabegger, Mujeeb Ullah, Reinhard Schwoediauer, Alexander Mumyatov, Marius Bodea, Jeffrey W. Fergus, Vladimir F. Razumov, Helmut Sitter, Siegfried Bauer, Niyazi Serdar Sariciftci. Environmentally sustainable organic field effect transistors1991-1998
Arnaud Maillard, Alain Rochefort. Band alignment engineering in organized rrP3HT/C₆₀ bulk heterojunction
Abstract:
The influence of structural ordering in a blend of rrP3HT polymer and C₆₀ molecules has been investigated with first principles DFT calculations. An increasing packing density of rrP3HT chains and C₆₀ component favors an increasing open-circuit voltage (V_oc), leaving the absorption properties of rrP3HT nearly intact. In contrast, an increasing size of п-crystal domains of rrP3HT within the blend tends to strongly enhance the magnitude of п-electron delocalization, leading to a decrease of both the rrP3HT band gap and V_oc.1999-2011
M. Gruber, B.A. Stickler, G. Trimmel, F. Schürrer, K. Zojer. Impact of energy alignment and morphology on the efficiency in inorganic–organic hybrid solar cells
Abstract:
Carrier transport in hybrid inorganic–organic solar cells has been studied by means of a two-dimensional drift-diffusion-based model including the generation and motion of excitons. The devices consist of a polymer serving as donor material and a semiconducting small-band gap inorganic component as acceptor material. For the first time it is taken into account that, in strong contrast to purely organic or inorganic cells, charge carriers can be generated at the heterojunction (due to dissociation of the donor excitons) and in the bulk of the acceptor material (due to band to band generation in the inorganic material). The efficiencies of devices were investigated dependent on (i) the donor–acceptor interface geometry, (ii) the transport level offsets at the heterojunction, and (iii) the energy barriers formed at the contacts. For each case, a detailed analysis of the behavior is given. We demonstrate that, depending on the particular scenario, each of these three factors can be responsible for profoundly reduced efficiencies and pronounced s-shaped sections in the I–V curves. Moreover, we show that each of the investigated factors may give rise to equally serious efficiency losses. However, it is not possible to identify a dominant effect. Depending on the particular combination, the efficiency can vary by two orders of magnitudes. In order to avoid such losses, our theoretical assessment reveals that suitable material combinations are required to form (i) ohmic contacts, (ii) preclude formation of isolated islands or nanoparticles during growth, and (iii) possess a hole-blocking offset in the transport levels at the heterojunction.2012-2018
Umberto Giovanella, Paolo Betti, Alberto Bolognesi, Silvia Destri, Manuela Melucci, Mariacecilia Pasini, William Porzio, Chiara Botta. Core-type polyfluorene-based copolymers for low-cost
light-emitting technologies
Abstract:
Single layer white organic light emitting diodes (WOLED) are obtained with a polymeric blend, whose constituents are three polyfluorene (PF) based materials emitting in the three fundamental colours thanks to the insertion of a single monomeric unit with different chemical nature at the core of the PF chain. The peculiar choice of three fully compatible polymers allows us to obtain stable and homogeneous active layers for highly performing WOLEDs. The high quality white electroluminescence with chromaticity coordinates (0,32; 0,33), correlated colour temperature of 5893 K and colour rendering index of 90, makes these compounds good candidates for low-cost solid-state lighting technologies.2019-2025
I. Hancox, P. Sullivan, K.V. Chauhan, N. Beaumont, L.A. Rochford, R.A. Hatton, T.S. Jones. The effect of a MoO_x hole-extracting layer on the performance of organic photovoltaic cells based on small molecule planar heterojunctions
Abstract:
We report a significant increase in the open circuit voltage (V_oc) and power conversion efficiency in both chloroaluminium phthalocyanine (ClAlPc)/fullerene (C₆₀) and boron subphthalocyanine chloride (SubPc)/C₆₀ organic photovoltaic (OPV) cells with the insertion of a thin molybdenum oxide (MoO_x) hole-extracting layer. This improvement was not seen with copper phthalocyanine (CuPc)/C₆₀, and the addition of the MoO_x layer leads to reduced device performance for pentacene/C₆₀ cells. Cells containing the MoO_x layer demonstrated significantly improved stability compared to the cells deposited on bare indiumtin oxide (ITO). External quantum efficiency (EQE) measurements taken before and after constant AM1,5G illumination for 60 min showed reduced current losses for all cells containing the MoO_x layer, especially in spectral regions where the donor layer contributes. We attribute this improvement to the increased stability at the MoO_x/donor interface.2026-2031
Wonsuk Choi, Min-Hoi Kim, Yu-Jin Na, Sin-Doo Lee. Complementary transfer-assisted patterning of high-resolution heterogeneous elements on plastic substrates for flexible electronics
Abstract:
We developed a versatile platform to construct heterogeneous organic and metallic elements with micrometer features on a plastic substrate in a complementary transferassisted patterning (CTAP) scheme. The underlying concept relies on a high-resolution transfer-printing process of a sacrificial layer, producing complementary patterns of the elements, in combination with a lift-off technique for removing the sacrificial layer to leave only active patterns on a variety of substrates. No detrimental errors in sequentially defining patterns of both an organic material and a metal are involved during lifting-off the sacrificial layers in multilayer architecture. We demonstrated the generic principle of the CTAP in the fabrication of short-channel organic thin film transistors on glass substrates and organic inverters on plastic substrates for flexible electronics.2032-2036
Suman Banerjee, S. Sundar Kumar Iyer. Short-circuit current density and spectral response modelling of bulk-heterojunction solar cells
Abstract:
A general model to calculate short circuit current and spectral response of the bulk-heterojunction solar cell is discussed here. In order to get the short circuit current density at each wavelength the generation rate of electron and holes are calculated by the optical modelling based on transfer matrix approach. The drift–diffusion equation is then solved to get the current density at each wavelength using the calculated generation rate. Spectral response is found to be very similar to the experimental data of (3-hexylthiophene) (P3HT): [6,6]-phenyl C₆₁-butyric acid methylester (PCBM) based bulk-heterojunction solar cell. The variation of short circuit current as a function of active layer thickness has been calculated using the model which matches with the experimental observations taken from literature. The sub-linear dependence of short circuit current on incident light intensity has also been explained by the model.2037-2044
Alejandro de la Fuente Vornbrock, Donovan Sung, Hongki Kang, Rungrot Kitsomboonloha, Vivek Subramanian. Fully gravure and ink-jet printed high speed pBTTT organic thin film transistors
Abstract:
Organic thin film transistors with channel lengths below 20 lm have been fabricated on plastic substrates using a combination of rotogravure and ink-jet printing exclusively. Gravure is utilized to deposit thin, smooth, and narrow metal lines ideal for gate electrodes; a poly(4-vinylphenol) dielectric; and a poly(2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT) semiconductor using a heated roll. A novel fluid guiding technique is used to maintain closely spaced ink-jet printed source and drain (S/D) contacts. Together these printing processes yield aggressively scaled yet easily manufacturable TFTs with operating frequencies of 18 kHz.2045-2054
J.A. Mikroyannidis, D.V. Tsagkournos, S.S. Sharma, Y.K. Vijay, G.D. Sharma. Conjugated small molecules with broad absorption containing pyridine and pyran units: Synthesis and application for bulk heterojunction solar cells
Abstract:
Two new conjugated small molecules (SMs), M1 and M2, of low band gap with pyridine and pyran units, respectively, were synthesized by a convenient two-step reaction. They were soluble in common organic solvents and showed broad absorption ranging from 300 to 750 nm. Their long-wavelength absorption maximum was at 601–640 nm and the optical band gap was 1,60–1,67 eV. These SMs and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) were used as donor and acceptor respectively to fabricate bulk heterojunction organic photovoltaic (OPV) devices through solution processing. The power conversion efficiencies (PCEs) for the OPV devices based on the as cast M1:PCBM and M2:PCBM are 1,42% and 1,80%, respectively. The higher PCE for the M2:PCBM based devices is attributed to the higher hole mobility, broader absorption spectra and lower band gap of M2 as compared to M
1. The PCEs have been improved up to 1,75% and 2,18% for the solvent treated M1:PCBM and M2:PCBM blends, respectively. Finally, they have been further enhanced to 2,03% and 2,77% for the thermally annealed solvent treated M1:PCBM and M2:PCBM blends, respectively. This improvement has been attributed to the increase in the crystallinity of the blend and balance charge transport of the devices based on the solvent treated and thermally annealed solvent treated blends.2055-2059
Guohua Xie, Zhensong Zhang, Qin Xue, Shiming Zhang, Li Zhao, Yang Luo, Ping Chen, Baofu Quan, Yi Zhao, Shiyong Liu. Highly efficient top-emitting white organic light-emitting diodes with improved contrast and reduced angular dependence for active matrix displays
Abstract:
Highly efficient top-emitting white organic light-emitting diodes (TEWOLEDs) on silicon substrates based on complementary blue and yellow phosphors are demonstrated. The bottom copper anode with medium reflectance, which is compatible with standard complementary metal oxide semiconductor (CMOS) technology, and the semitransparent cathode with a top capping layer, are introduced to facilitate white light emission with improved contrast and reduced angular dependence. Both TEWOLEDs, with and without the capping layers, exhibit nearly lambertian-type emission. The spectrum of TEWOLED with a capping layer is similar to that of the bottom-emitting counterpart. Our TEWOLED reaches high efficiencies of 27,7 cd/A and 17,6 μm/W at a current density of 10 mA/cm², and low voltage of 4,4 V at 1000 cd/m².