Organic Electronics 2011 Volume 12 №10

Elsevier. — 159 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.Kyoung Soo Yook, Jun Yeob Lee. High efficiency in solution processed blue phosphorescent organic light-emitting diodes using an alcohol soluble emitting layer
Abstract:
High efficiency solution processed blue and deep blue phosphorescent organic light-emitting diodes (PHOLEDs) were developed using an alcohol soluble 2,7-bis(diphenylphosphoryl)-9-phenyl-9H-carbazole (PPO27) as the host material for the emitting layer. Iridium(III) bis (4,6-(di-fluorophenyl)-pyridinato-N,C') picolinate (FIrpic) and iridium(III) bis((3,5-difluoro-4-cyanophenyl)pyridinato-N,C') picolinate (FCNIrpic) were doped into the PPO27 host using 2-propanol as the solvent for the emitting layer. The alcohol soluble PPO27:FIrpic and PPO27:FCNIrpic emitting layers could form an orthogonal film with an organic soluble hole transport layer and high quantum efficiency of 14,6% and 13,4% was achieved in the PPO27:FIrpic and PPO27:FCNIrpic devices, respectively. Sky blue color coordinate of (0,15, 0,36) was obtained in the PPO27:FIrpic device, while blue shifted color coordinate of (0,15, 0,26) was realized in the PPO27:FCNIrpic device.1600-1605
Yasuaki Tokudome, Tatsuya Fukushima, Atsushi Goto, Hironori Kaji. Enhanced hole injection in organic light-emitting diodes by optimized synthesis of self-assembled monolayer
Abstract:
The purpose of the present study is to demonstrate that formation conditions for a selfassembled monolayer (SAM) on indium tin oxide (ITO) highly influence the device performance of organic light-emitting diodes (OLEDs). An ITO substrate was modified with a silane modifier under systematically controlled conditions. Pentyltriethoxysilane (PTES) and tetrahydrofuran (THF) were used as a surface modifier and a solvent, respectively. The immobilization of PTES on the ITO substrate was performed under both the acidic and basic conditions with various H₂O/PTES ratios, r. The relationship between the resultant SAM structure and the hole-injection property was investigated by using hole only devices (HODs) fabricated on the SAM-modified ITO substrate. It was found that the catalytic condition, the value of r, and the concentration of PTES highly influence the structure of obtained SAM, and thus affect the hole-injection property of HOD. The SAM formation under the acidic conditions allows homogeneous coverage of a silane layer on the ITO surface, which leads to the improved hole-injection from the anode. On the other hand, the use of basic catalysts results in the inhomogeneous coverage of a silane layer on the ITO surface and the decreased hole-injection from the anode. The choice of r and the concentration of PTES also affect the kinetics of hydrolysis and condensation reactions of PTES, and hence affects the resultant SAM structure and hole-injection property. The results obtained here show that the device performance can be improved drastically by choosing the SAM formation conditions appropriately, even in the case that particular and novel modifiers are not employed.1606-1611
Jing Zeng, Ke-Qiu Chen, Jun He, Xiao-Jiao Zhang, W.P. Hu. Rectifying and successive switch behaviors induced by weak intermolecular interaction
Abstract:
By applying nonequilibrium Green’s functions in combination with density-function theory, we investigate the effect of the weak intermolecular interaction on electronic transport properties in a bilayer graphene nanoribbon device. The results show that a successive switch behavior can be realized by adjusting the weak п–п interaction between two graphene nanoribbon molecules. Moreover, rectifying behavior can be observed in such systems. The mechanisms for these phenomena are suggested.1612-1618
Thomas Winkler, Hans Schmidt, Harald Flügge, Fabian Nikolayzik, Ihno Baumann, Stephan Schmale, Thomas Weimann, Peter Hinze, Hans-Hermann Johannes, Torsten Rabe, Sami Hamwi, Thomas Riedl, Wolfgang Kowalsky. Efficient large area semitransparent organic solar cells based on highly transparent and conductive ZTO/Ag/ZTO multilayer top electrodes
Abstract:
We present transparent multilayer electrodes prepared by RF sputtering of zinc tin oxide (ZTO) and thermal evaporation of silver (Ag) as top contact for organic electronics. Specifically we study the electrical, optical and structural properties of the ZTO/Ag/ZTO (ZAZ) electrode. In the first step, we analyze the origin of high conductivity and high transparency by studying structural, electrical and optical properties of ultra thin Ag films. Secondly, we demonstrate that continuous and highly conductive Ag films can be deposited down to a thickness of 6 nm on top of ZTO. Furthermore we show, that owing to the stabilizing effect of the sputtered ZTO cap, ZAZ is substantially more robust than ZTO/Ag (ZA). As a first result we achieve a low sheet resistance of 5 X/sq and a transmissivity of 82% in the visible region of light. These values are compared to common transparent and semitransparent electrode materials deposited at room temperature like indium tin oxide (ITO). As an application we realized an optimized ZAZ structure as highly conductive and transparent top contact for large area semitransparent bulk hetero junction (BHJ) polymer solar cells (OSC) with an inverted device architecture. To expose the outstanding properties of the novel multilayer electrode we compare semitransparent OSCs using common ITO and ZAZ as top electrode cells with a large cell area 2 cm².1619-1624
Run-Feng Chen, Guo-Hua Xie, Yi Zhao, Sheng-Lan Zhang, Jun Yin, Shi-Yong Liu, Wei Huang. Novel heterofluorene-based hosts for highly efficient blue electrophosphorescence at low operating voltages
Abstract:
A novel concept for molecular design of blue host materials for phosphorescent OLEDs (PHOLEDs) by combining carbazole and heterofluorene via structurally mimicking 4,4'-N,N'-dicarbazole-biphenyl (CBP) was presented. The carbazole end-capped heterofluorenes (CzHFs) prepared accordingly in high yields, were found to be ideal hosts for blue PHOLEDs. At the brightness level of 1000 and 5000 cd m^-2, the driving voltages are still lower than 4,5 V with the external quantum efficiencies retain as high as 18,1% and 16,8% respectively.1625-1631
Elif Kose Unver, Simge Tarkuc, Yasemin Arslan Udumd, Cihangir Tanyeli, Levent Toppare. The effect of the donor unit on the optical properties of polymers
Abstract:
A series of donor–acceptor–donor (DAD) type п-conjugated monomers containing 10,11,12,13-tetrahydrodibenzo[a,c]phenazine moiety in the backbone as the acceptor unit and thiophene derivatives as the donor unit were prepared by Stille coupling. Thiophene, 3-hexyl thiophene and 3,4-ethylenedioxythiophene were used as the donor units to understand the effects of donor unit on electrochemical and optoelectronic properties of the resulting polymers. Electroactivity of monomers and redox behavior of their polymers were investigated by cyclic voltammetry. The presence of the strong electron-donating ethylenedioxy groups on the aromatic structure increased electron density on 2,7-bis (2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-10,11,12,13-tetrahydrodibenzo[a,c]phenazine (DTBP), thus the oxidation potential of DTBP shifts to a lower value than that of 2,7-bis (4-hexylthiophen-2-yl)-10,11,12,13-tetrahydrodibenzo[a,c] phenazine (HTBP) and 2,7-di (thiophen-2-yl)-10,11,12,13-tetrahydrodibenzo[a,c]phenazine (TTBP). The electronic band gaps, defined as the onset of the п–п* transition, were found to be 2,5 eV for HTBP, 2,0 eV for DTBP and 2.2 eV for TTBP. Both of PDTBP and PTTBP films showed multi-color electrochromism and also fast switching times ( 1 s) in the visible and NIR regions.1632-1637
Heng-Tien Lin, Chang-Yu Lin, Zingway Pei, Jun-Rong Chen, Yi-Jen Chan, Yung-Hui Yeh, Chung-Chih Wu. Investigating carrier transport paths in organic nonvolatile bistable memory by optical beam induced resistance change
Abstract:
The so-called optical beam induced resistance change (OBIRCH) method, a non-destructive characterization method, was adopted to investigate the spatial distribution of current transport paths in Au nanoparticle nonvolatile bistable memory devices. In scanning a laser beam to induce local changes of the temperature and the electronic/conduction properties, simultaneously the current change of the device (under the constant bias voltage) at each scanning step was recorded to visualize the distribution of the current conduction paths. The results reveal that in the memory devices using polymer-stabilized Au nanoparticles, the current transport paths during the writing mode or the subsequent reading mode (of the ‘‘on’’ state) are localized, and that once the localized current transport paths are established in the writing mode, the current transport in the subsequent reading mode (of the ‘‘on’’ state) would basically follow the same paths. The established conduction paths would be eliminated in the erasing process and be re-established in the next writing process. Yet, the current conduction paths established for the ‘‘on’’ state are somehow random and vary from writing to writing. Results of this work might have significant implications to operation or applications of such memory devices. This work demonstrates that the OBIRCH technique might be an useful method to characterize localized current transport paths in organic devices.1638-1643
Hirohiko Fukagawa, Shiro Irisa, Hiromu Hanashima, Takahisa Shimizu, Shizuo Tokito, Norimasa Yokoyama, Hideo Fujikake. Simply structured, deep-blue phosphorescent organic light-emitting diode with bipolar host material
Abstract:
We developed an efficient, deep-blue phosphorescent organic light-emitting diode (POLED) with a simplified device structure using a new host material. There are only three organic layers in the deep-blue POLED, namely, a hole-transporting layer, an emitting layer and an electron-transporting layer. The new host material exhibits bipolar carrier transportability and high triplet energy. The POLED utilizes a phosphorescent guest material, iridium(III) bis(4',6',-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate, that exhibits an external quantum efficiency of about 13% and a power efficiency of about 15 μm/W at a current density of 0,1 mA/cm². The efficiencies of the POLED are comparable to those of conventional POLEDs consisting of at least four organic layers. The bipolar host material will be useful for simplifying the device structure of deep-blue POLEDs.1644-1648
Gert-Jan A.H. Wetzelaer, David Hartmann, Sonsoles García Santamaría, Marta Pérez-Morales, Alejandra Soriano Portillo, Martijn Lenes, Wiebke Sarfert, Henk J. Bolink. Combined thermal evaporated and solution processed organic light emitting diodes
Abstract:
Highly efficient, partly solution processed phosphorescent red, green and white organic light emitting diodes with small molecular weight host materials are prepared from commercially available starting compounds. Starting from an evaporated reference device, layers are stepwise replaced by solution processed layers. Replacing the evaporated hole transport layer by a solution processed polymer interlayer does not affect the performance and allows spincoating of the emissive layer after annealing of the polymer. Devices with, next to the spincoated hole injection and transport layer, a solution processed emission layer show similar characteristics and efficiencies as the reference device. Additionally, white light emitting devices are demonstrated in which the first emissive layer is solution processed, for which lifetimes in excess of 1000 h are achieved. Thus, we show that, in order to reduce production costs, solution processing can be used as an alternative to – and in conjunction with – Thermal evaporation.1649-1656
Evan S.H. Kang, Eunseong Kim. Effect of non-isothermal recrystallization on microstructure and transport in poly(thieno-thiophene)thin films
Abstract:
We present the effect of recrystallization rate on the microstructure and charge transport properties of high-performance semiconducting polymer, poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), thin films. Differential scanning calorimetry (DSC) measurements indicate that the cooling rate directly influences the recrystallization process. In addition, atomic force microscopy (AFM) studies with an X-ray diffraction diagram demonstrate that slow cooling leads to well-connected large domains with enhanced three-dimensionally ordered structures, whereas fast cooling results in misaligned small domains with rough surfaces. At various temperatures, transport characteristics show an increase in the charge carrier mobility and a reduction in the activation energy with decreasing cooling rate of the films. Cooling rates slower than 15 °C/min induce the saturation of mobility and activation energy. These results assert that the cooling rate is a crucial factor for ordering in a microstructure as well as for the high performance of polymer thin films.1657-1662
A. Aguirre, S.C.J. Meskers, R.A.J. Janssen, H.-J. Egelhaaf. Formation of metastable charges as a first step in photoinduced degradation in п-conjugated polymer:fullerene blends for photovoltaic applications
Abstract:
Photoinduced changes in solids films of P3HT and PCPDTBT are studied in order to elucidate the initial stage of photodegradation in polymer solar cells. We find that illumination of the polymers with either UV or visible light in the presence of air induces persistent radical cations on the polymer chains. The radical cations are identified by optical and electron paramagnetic resonance spectroscopy. The photoinduced charges are stable at room temperature for at least hours, but recombine rapidly upon removal of air from the sample chamber. We ascribe the persistent charges to P⁺-O₂^- charge pairs that are stabilized by chemical interactions between molecular oxygen and the polymer (P) Formation of persistent charges also takes place in the presence of the fullerene based electron acceptor PCBM.1663-1668
Michael Flämmich, Jörg Frischeisen, Daniel S. Setz, Dirk Michaelis, Benjamin C. Krummacher, Tobias D. Schmidt, Wolfgang Brütting, Norbert Danz. Oriented phosphorescent emitters boost OLED efficiency
Abstract:
The orientation distribution of the emissive sites in a phosphorescent Organic LED has been measured utilizing two independent optical methods. In contradiction to common expectations we find a clearly non-isotropic, predominantly parallel emitter orientation in the well-known triplet emitting guest–host system of Ir(MDQ)₂(acac) blended in an α-NPD matrix. This result emphasizes the necessity of more sophisticated assumptions on active emitter properties in quantitative optical OLED analysis, and demonstrates a highly promising approach for OLED efficiency optimization.1669-1673
Daniela Baierl, Bernhard Fabel, Paolo Lugli, Giuseppe Scarpa. Efficient indium-tin-oxide (ITO) free top-absorbing organic photodetector with highly transparent polymer top electrode
Abstract:
We report on an efficient solution-processable, top-absorbing organic photodetector with a polymer top electrode. The layer sequence is inverted, starting with the cathode as bottom electrode instead of an indium-tin-oxide (ITO) anode used in state-of-the-art organic detectors. The device comprises a bulk heterojunction of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) as photoactive layer and a double layer of different formulations of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The lower PEDOT:PSS layer reduces the thermally generated dark current and the upper layer acts as anode. To increase the conductivity of the highly transparent ( 90% at 500 nm wave length) PEDOT:PSS electrode ethylene glycol is added. The influence of the anode sheet resistance R_sheet on important photodiode characteristics is investigated. For Rsheet = 100 Ω/sq high external quantum efficiency ( 70% at 500 nm) and high cut-off frequencies ( 400 kHz) can be reached. The performance of these inverted organic photodetectors is shown to be equal to state-of-the-art non-inverted detectors containing an ITO anode.1674-1682
Qiujian Sun, Guifang Dong, Haoyan Zhao, Juan Qiao, Xiaohui Liu, Lian Duan, Liduo Wang, Yong Qiu. Modulated intermolecular electrostatic interaction and morphology transition in squarylium dyes based organic field-effect transistors
Abstract:
A series of indolium squarine dyes were studied as air-stable semiconductors in organic field-effect transistors. By modulating substituted groups and structural rigidity, a mobility of 4,8 x 10^-3 cm²/Vs was achieved in solution processed device and the highest mobility of 0,2 cm²/Vs was obtained in single crystal devices. By structural analysis and theoretical calculation, crystal packing mode was found to be associated with the electrostatic attraction and repulsion between positive and negative charge centers of the molecule. This electrostatic interaction drove the spontaneous intermolecular ordering in the film, and resulted in performance enhancement for ISQ transistors. Quantitative research between mobility and the area of polycrystalline regions revealed the dependence of transport ability on the continuity and uniformity of the crystalline phase.1683-1694
Frédéric Dumur, Gihane Nasr, Guillaume Wantz, Cédric R. Mayer, Eddy Dumas, Audrey Guerlin, Fabien Miomandre, Gilles Clavier, Denis Bertin, Didier Gigmes. Cationic iridium complex for the design of soft salt-based phosphorescent OLEDs and color-tunable light-emitting electrochemical cells
Abstract:
Phosphorescent Organic Light-Emitting Diodes (PhOLEDs) based on iridium (III) soft salt were designed and studied. Heteroleptic anionic iridium complex (A) was prepared with thiocyanate anions and cationic iridium complex (C) was synthesized with 4,4'-dinonyl-2,2'-byridine as the ancillary ligand. Electronic and spectroscopic properties of the resulting combination of soft salt C-A were investigated by mean of UV–visible absorption, fluorescence spectroscopy and cyclic voltammetry. DFT calculations were also performed and the electroluminescent performances evaluated. Light-emitting electrochemical cells (LECs) displaying color-variable emission were also obtained. This color tunability aroused from a modification of the molecular packing of the emissive layer with the temperature.1695-1700
Kihyun Kim, Jin Woo Lee, Suk Ho Lee, Yong Baek Lee, Eun Hei Cho, Hak-Seob Noh, Seong Gi Jo, Jinsoo Joo. Nanoscale optical and photoresponsive electrical properties of P3HT and PCBM composite nanowires
Abstract:
In this paper, we report on the fabrication, intrinsic characteristics, and photoresponsive electrical properties of heterojunction composite nanowires (NWs) consisting of p-type poly (3-hexylthiophene) (P3HT) and n-type [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM). The P3HT:PCBM heterojunction composite NWs were prepared through a wetting method based on an alumina nanoporous template. The nanoscale optical and structural properties of the single NW were investigated using laser confocal microscope Raman and photoluminescence spectra. The photoresponsive current–voltage (I-V) characteristics of the P3HT:PCBM single NW were measured by means of Au–Al electrode patterns. For the P3HT:PCBM single NW, the I-V characteristics in the dark condition showed diode-like behaviors due to the formation of energy barriers. Under light illumination, the current level of the P3HT:PCBM single NW was enhanced at a relatively high applied bias (P10 V). The photovoltaic effect was observed for the solar cells using P3HT:PCBM composite NWs and the maximum power conversion efficiency was estimated to be 0,14%.1701-1710
Fatma Baycan Koyuncu, Sermet Koyuncu, Eyup Ozdemir. A new multi-electrochromic 2,7 linked polycarbazole derivative: Effect of the nitro subunit
Abstract:
A new poly-2,7-di-2-thienyl-9H-carbazole derivative (poly(TCT-N)) bearing nitro (–NO₂) subunit has been reported. The electrochemical and optical properties of TCT-N monomer and its polymer have been compared to the 9-phenyl-2,7-di-2-thienyl-9H-carbazole (TCT) standard molecule. Cyclic voltammetry revealed that TCT-N and TCT have excellent polymerization activity; due to extended conjugation with the attached thiophene unit and also their low oxidation potentials. The oxidation potential of TCT-N is higher than that of TCT, because of electro-withdrawing effect of –NO₂ moiety. Besides, the TCT-N polymeric film prepared via electrochemical process exhibits a multi-electrochromic behavior compared with TCT standard molecule. The electroactive orange color of poly-TCT-N film converted respectively to green, turquoise and dark blue upon applied positive potentials. Consequently, the polymeric electrochrome exhibits multi-electrochromic behavior, high redox stability, high coloration efficiency and reasonable response time for electrochromic applications.1711-1715
Kyoung Soo Yook, Jun Yeob Lee. Solution processed deep blue phosphorescent organic light-emitting diodes with over 20% external quantum efficiency
Abstract:
Highly efficient solution processed deep blue phosphorescent organic light-emitting diodes (PHOLEDs) were developed using a solution processible high triplet energy host and deep blue dopant materials. Stable film morphology was observed from the spin coated deep blue emitting layer and a high quantum efficiency of 22,1% was achieved in the deep blue PHOLED with a color coordinate of (0,14, 0,19).1716-1723
Hong Huang, Qiang Fu, Shaoqing Zhuang, Guangyuan Mu, Lei Wanga, Jiangshan Chen, Dongge Ma, Chuluo Yang. Solution-processable 1,3,5-tri(9-anthracene)-benzene cored propellershaped materials with high T_g for blue organic light-emitting diodes
Abstract:
This study describes the synthesis and characterization of a series of new blue fluorescent materials, with propeller-like topology, consisting of 1,3,5-tri(9-anthracene)benzene core and various aromatic dendrons, such as naphthalene, 3,5-diphenylbenzene, carbazole, and N,N-diphenylamine. These compounds show excellent thermal and morphological stability with high glass transition temperatures (T_g) (166–231 °C) and high thermal decomposition temperatures (T_d) (427–504 °C). Solution-processable double-layered OLEDs fabricated with these materials as the light-emitting layer show stable blue emission and good performance. The nondoped electronic device fabricated using compound 5c exhibits a maximum brightness of 4754 cd/m² and maximum current efficiency of 2,0 cd/A (power efficiency, 1,71 μm/W) with Commission Internationale d’Eclairage (CIE_x,y) color coordinates of (x = 0,16, y = 0,19) and the devices’ threshold voltage are only 3,4 eV. Compound 5d shows an even higher efficiency of up to 4,90 cd/A with CIEx,y color coordinates of (x = 0,17, y = 0,31) when doped with a blue fluorescent dopant, 4,4'-bis[4-(di-p-tolylamino) styryl]biphenyl (DPAVBi).1724-1730
Xuhai Liu, Jakob Kjelstrup-Hansen, Henri Boudinov, Horst-Günter Rubahn. Charge-carrier injection assisted by space-charge field in AC-driven organic light-emitting transistors
Abstract:
Organic light-emitting transistors can be operated by an alternating gate voltage to provide high light output intensity. We propose a model for the light generation process in such light-emitting transistors based on systematic measurements of how the light output intensity depends on the biasing parameters. Following injection of holes, which form a positively charged space-charge region, subsequent electron tunneling from the same metal electrode eventually leads to light emission from the organic emitter. The electron injection is found to depend on the positive space-charge region, and the hole injection efficiency therefore strongly influences the emission intensity. Low temperature measurements show increased emission intensity as the temperature decreases indicating that the light generation is dependent on thermally activated charge injection, i.e., Fowler– Nordheim tunneling theory is not applicable. Further metal/semiconductor interface modification could result in optimized charge injection under AC biasing, thus leading to more efficient organic light-emitting devices.1731-1735
Chengliang Wang, Xiaomu Wang, Jie Min, Ni Zhao, Jianbin Xu. Super-linear rectifying property of rubrene single crystal devices
Abstract:
We have observed a rectifying behavior in a lateral symmetrical device structure based on rubrene single crystals. Our analysis shows that the rectifying characteristics are not due to formation of Schottky junction between the electrode and the organic semiconductor, but should be attributed to a mechanism that is similar to the super-linear operation regime in organic field-effect transistors. Furthermore, we have demonstrated that this rectifying behavior can be turned on and off via modulation of the density of space charge in the organic semiconductor/substrate interface, which essentially affects the threshold voltage (V_T). Our results demonstrate a simple approach that can potentially be used to fabricate organic rectifiers without application of multi-layer device structure such as MOSFET diode.1736-1745
Bettina Friedel, Thomas J.K. Brenner, Christopher R. McNeill, Ullrich Steiner, Neil C. Greenham. Influence of solution heating on the properties of PEDOT:PSS colloidal solutions and impact on the device performance of polymer solar cells
Abstract:
We have investigated the effects of temperature variation on colloidal solutions of the electrode polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) and its consequences for photovoltaic devices using conjugated polymer blends as the photoactive material. By variation of the PEDOT:PSS solution temperature between 20 and 90 °C we observed reversible temperature-dependent change in size of the PEDOT:PSS particles. This process is associated with temperature and concentration dependent phase transitions of the PSS electrolyte chains. We found optimum device performance, in particular high quantum efficiency and power conversion efficiency for solar cells, with PEDOT:PSS layers produced from 70 °C solutions. After consideration of film morphology, particle size, conductivity and work function, we conclude that improved device performance originates from enhanced conductivity in films deposited from heated solutions. While film conductivity increases mo\notonically with solution temperature, devices produced using solution temperatures greater than 70 °C suffer from the increased work function of the PEDOT:PSS layer.1746-1753
S. van Reenen, R.A.J. Janssen, M. Kemerink. Doping dynamics in light-emitting electrochemical cells
Abstract:
A major drawback of light-emitting electrochemical cells (LECs) is the long time scale associated with switching, during which ions redistribute in the active layer. We present a numerical modeling study that gives fundamental insight in the dynamics during turnon. The characteristic response of LECs to an applied bias is the electrochemical doping of the active layer by doping fronts moving across the active layer. Formation and motion of such doping fronts are shown to be intimately related to both the electronic and ionic mobility and therefore provide useful information regarding these two quantities in LECs. In particular, it is shown that the switch-on time in LECs is directly related to the time an ion needs to cross approximately half the device, enabling the extraction of the ion mobility from the switch-on time.