Organic Electronics 2009 Volume 10 №06

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.1041-1047
Dae Sung Chung, Dong Hoon Lee, Jong Won Park, Jaeyoung Jang, Sooji Nam, Yun-Hi Kim, Soon-Ki Kwon, Chan Eon Park. Phase-separated polydimethylsiloxane as a dielectric surface treatment layer for organic field effect transistors
Abstract:
We suggest a novel method for treating the surfaces of dielectric layers in organic field effect transistors (OFETs). In this method, a blend of poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) and dimethylsiloxane (DMS) with a curing agent is spin coated onto the surface of a dielectric substrate, silicon oxide (SiO₂), and then thermally cured. X-ray photoelectron spectroscopy, contact angle measurements, and morphology analysis were used to show that the hydrophilic DMS layer is preferentially adsorbed on the SiO₂ substrate during the spin coating process. After thermal curing, the bottom DMS layer becomes a hydrophobic PDMS layer. This bottom PDMS layer becomes thinner during curing due to the upward motion of the hydrophobic PDMS molecules. The FET mobility of the cured system was 10^-2 cm²/Vs, which is similar to that of polymeric semiconductors on octadecyltrichlorosilane treated SiO₂ dielectric layers. We also discuss the possibility of using this blend method to increase the air-stability of polymeric semiconductors.1048-1053
Bao Lei, Wei Lek Kwan, Yue Shao, Yang Yang. Statistical characterization of the memory effect in polyfluorene based non-volatile resistive memory devices
Abstract:
Non-volatile resistive memory devices based on a polyfluorene layer sandwiched between two electrodes were studied. The working mechanism was ascribed to the formation of metallic filaments. We characterized the switching probability of multiple devices and the consistency of the switching capability within the same device. Together with crosssection scanning electron microscope images and finite element simulation of electric field distributions, a model was developed to describe the resistive switching phenomenon and explain the variations between devices as well as between switching cycles.1054-1059
An Li, Shu-Hao Wena, Jun-Ling Song, Wei-Qiao Deng. Synthesis of cyanated tetracenes as the organic semiconductors
Abstract:
Two novel and air-stable cyanated tetracene derivatives, 5-cyanotetracene (1CT) and 5,11-dicyanotetracene (2CT), were synthesized as high-performance organic semiconductors. The stability of 2CT was evaluated by NMR and the electrochemical property was investigated by cyclic voltammetry (CV) and UV–vis spectrum. The reorganization energy of 2CT predicted by UB3LYP/6-311g(d,p) is 0,0881 eV, which is the lowest among existing compounds. The X-ray crystallographic analysis revealed that the 2CT single crystal has a promising face-to-face packing with a relative short intermolecular distance of 3,403 Å. Based on the theoretical model we previously developed, the calculated hole mobilities of these air-stable cyanated tetracene derivatives in a–b plane are 2,9 cm² V^-1 s^-1 for 1CT and 2,2 cm² V^-1 s^-1 for 2CT, respectively. These oxygen-resisted organics may offer potential to fabricate the flexible electronics under air conditions.1060-1065
Jing-Shun Huang, Chen-Yu Chou, Meng-Yueh Liu, Kao-Hua Tsai, Wen-Han Lin, Ching-Fuh Lin. Solution-processed vanadium oxide as an anode interlayer for inverted polymer solar cells hybridized with ZnO nanorods
Abstract:
Solution-processed vanadium oxide (V₂O₅) as an anode interlayer is introduced between the organic layer and the Ag electrode for improving the performance of the low-cost inverted polymer solar cells hybridized with ZnO nanorods. Our investigations indicate that the solution-processed V₂O₅ interlayer as an electron-blocking layer can effectively prevent the leakage current at the organic/Ag interface. The power conversion efficiency is improved from 2,5% to 3,56% by the introduction of the V₂O₅ interlayer. The V₂O₅ interlayer also serves as an optical spacer to enhance light absorption, and thereby increases the photocurrent. Compared to the vacuum-deposited techniques, the fabrication of the solution-processed V₂O₅ interlayer is simple and effective. The solution-based approach makes it attractive for applications to mass production and potentially printed organic electronics.1066-1073
Sung Ouk Jung, Qinghua Zhao, Jong-Won Park, Seul Ong Kim, Yun-Hi Kim, Hyoung-Yun Oh, Jinho Kim, Soon-Ki Kwon, Youngjin Kang. A green emitting iridium(III) complex with narrow emission band and its application to phosphorescence organic light-emitting diodes (OLEDs)
Abstract:
The homoleptic Ir(III) complex, fac-tris{2-(3'-trimethylsilylphenyl)-5-trimethylsilylpyridinato} iridium, has been synthesized and characterized to investigate the effect of the substitution of bulky silyl groups on the photophysical properties and electroluminescence (EL) characteristics of Ir(ppy)₃ (ppy = 2-phenylpyridine). The absorption, emission, cyclic voltammetry and electroluminescent performance of the complex have also been evaluated. A power efficiency of 17,3 lm/W at 10 mA/cm² compared to 11,7 lm/W for Ir(ppy)₃ is achieved with the new complex as a dopant in phosphorescent organic light-emitting diodes (OLEDs). In addition, the complex shows a narrow emission band of a small full width at half-maximum (fwhm, ca. 50 nm) value.1074-1081
Vincenzo Vinciguerra, Manuela La Rosa, Donata Nicolosi, Giovanni Sicurella, Luigi Occhipinti. Modeling the gate bias dependence of contact resistance in staggered polycrystalline organic thin film transistors
Abstract:
We have modeled the dependence on the gate voltage of the bulk contact resistance and interface contact resistance in staggered polycrystalline organic thin film transistors. In the specific, we have investigated how traps, at the grain boundaries of an organic semiconductor thin film layer placed between the metal electrode and the active layer, can contribute to the bulk contact resistance. In order to the take into account this contribution, within the frame of the grain boundary trapping model (GBTM), a model of the energy barrier E_B, which emerges between the accumulation layer at the organic semiconductor/insulator interface and injecting contact, has been proposed. Moreover, the lowering of the energy barrier at the contacts interface region has been included by considering the influence of the electric field generated by the accumulation layer on the injection of carriers at the source and on the collection of charges from the accumulation layer to the drain contact. This work outlines both a Schottky barrier lowering, determined by the accumulation layer opposite the source electrode, as well as a Poole-Frenkel mechanism determined by the electric field of the accumulation layer active at the drain contact region. Finally it is provided and tested an analytical equation of our model for the contact resistance, summarizing the Poole-Frenkel and Schottky barrier lowering contribution with the grain boundary trapping model.1082-1090
Yang Liu, Xutang Tao, Fuzhi Wang, Xiangnan Dang, Dechun Zou, Yan Ren, Minhua Jiang. Parallel H-shaped phenylenevinylenes: Quasi-coplanar molecules for highly luminescent blue OLEDs
Abstract:
For highly luminescent solid-state applications, the twisted or spiro-configured conjugated molecules are mostly considered as the proper choices because the coplanar ones usually have intensively intermolecular п–п interactions, which lead to fluorescence quenching and red-shift. In this study, the two prepared parallel H-shaped phenylenevinylenes with coplanar configuration show the special case. Due to their characteristics of multibranches, these coplanar multi-branched molecules prefer to form stable amorphous morphology in thin films were verified by the XRDs and AFM. The amorphous thin films show very weak intermolecular actions, with intrinsic differences on both steady and transient optical properties from the crystalline states. The non-doped electroluminescent devices based on them show highly luminescent blue emissions. Both their luminance (20490 cd m^-2) and efficiency (2,8 cd A^-1/2,6 μmW^-1) are comparable with the performances of the cross dimeric OPVs which have similar constructing blocks to the H-shaped molecules and with the same EL device configurations.1091-1096
Nam Su Kang, Byeong-Kwon Ju, Changhee Lee, Jae-Pyoung Ahn, Byung Doo Chin, Jae-Woong Yu. Partitioning of the organic layers for the fabrication of high efficiencyorganic photovoltaic devices
Abstract:
Lateral partitioning of hole extraction layer with insulating walls improved the power conversion efficiency of organic photovoltaic device. When the conductivity of the hole extraction layer is low, no improvement is obtained by partitioning. However, when the conductivity is high, a significant improvement was obtained in the partitioned cells, showing the estimated power conversion efficiency of 4,58% compared to the 3,54% of the single cell structure. This improvement, carefully corrected by masking at measurement, could be explained by the reduction of series resistance. Although accurate estimation of device area at partitioned device might be difficult, its effectiveness on the properties of large area organic photovoltaic device is clear, as shown in the result of 1 cm²-size cell with the same manner.1097-1101
Fei Hong, Xinan Guo, Hao Zhang, Bin Wei, Jianhua Zhang, Jun Wang. Preparation of highly oriented copper phthalocyanine film by molecular templating effects for organic field-effect transistor
Abstract:
Highly oriented copper phthalocyanine (CuPc) film consisting of many crystal domains was prepared by introducing titanyl-phthalocyanine (TiOPc) as molecular template at high substrate temperature. CuPc molecules stand up on the top of TiOPc domains exhibiting herringbone structure and high-order arrangement investigated by atomic force microscopy and X-ray diffraction. Then organic transistors were fabricated that exhibited improved device performances, a 0,12 cm²/V s of mobility and a 10⁵ of on/off ratio. Furthermore, template thickness dependence on device performance was disclosed. These results indicated that molecular template is a very effective method to prepare high-mobility organic semiconductor film.1102-1108
Sung Kyu Park, Yong-Hoon Kim, Jeong-In Han. High-resolution patterned nanoparticulate Ag electrodes toward all printed organic thin film transistors
Abstract:
High-resolution patterned nanoparticulate Ag electrode arrays and all printed organic thin film transistors (OTFTs) were demonstrated using a simple dip-casting and a photoresistfree, non-relief-pattern lithographic process. An octadecyltrichlorosilane self-assembled monolayer was deposited to provide low surface energy and patterned by deep ultraviolet light, resulting in reproducible periodic arrays of patterned hydrophilic domains separated from hydrophobic surroundings. Using a simple dip-casting with optimal withdrawal speed, viscosity, and solvent polarity, dot size and electrode width of less than 1 lm and 5 μm were obtained, respectively. All printed OTFTs were fabricated. Ink-jet printed 6,13-bis(triisopropyl-silylethynyl) pentacene OTFTs including high-resolution patterned nanoparticulate Ag source/drain electrodes (L 10 lm) have shown similar performance to the OTFTs with photolithographically patterned electrodes.1109-1115
Jen-Hsien Huang, Kuang-Chieh Li, Hung-Yu Wei, Po-Yen Chen, Lu-Yin Lin, Dhananjay Kekuda, Hong-Cheu Lin, Kuo-Chuan Ho, Chih-Wei Chu. Efficient bulk heterojunction solar cells based on a low-bandgap polyfluorene copolymers and fullerene derivatives
Abstract:
A low-bandgap polymer (PF-PThCVPTZ) consisted of fluorene and phenothiazine was designed and synthesized. With the donor–acceptor segment, the partial charge transfer can be built in the polymer backbone leading to a wide absorbance. The absorption spectrum of PF-PThCVPTZ exhibits a peak at 510 nm and an absorption onset at 645 nm in the visible range. As blended with [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) as an electron acceptor, narrow bandgap PF-PThCVPTZ as electron donor shows significant solar cell performance. Under AM 1,5 G, 100 mA/cm² illumination, a power conversion efficiency (PCE) of 1,85% was recorded, with a short circuit current (J_SC) of 5,37 mA/cm², an open circuit voltage (V_OC) of 0,80 V, and a fill factor (FF) of 43,0%.1116-1119
Arup K. Rath, Amlan J. Pal. To induce negative differential resistance in organic devices through a ferroelectric polymer
Abstract:
We report how ferroelectric materials induce negative differential resistance (NDR) in organic devices. Fluorescein, which exhibits semiconducting current–voltage characteristics, shows NDR effect in a ferroelectric matrix. Here, we vary the concentration of fluorescein in the ferroelectric matrix to study its effect on NDR. We also show how the degree of polarization controls NDR. We infer that under a suitable bias, the ferroelectric polymer becomes polarized to facilitate electron-injection in the device followed by a double-reduction of fluorescein molecules. From the capacitance–voltage measurements, we substantiate the role of polarization in inducing NDR effect in organic molecules.1120-1132
Mariano Campoy-Quiles, Yoshihiro Kanai, Ahmed El-Basaty, Heisuke Sakai, Hideyuki Murata. Ternary mixing: A simple method to tailor the morphology of organic solar cells
Abstract:
We present a detailed study of the effects of ternary mixing on blend morphology, charge carrier mobility and organic solar cell performance. We investigate ternaries consisting of regio random poly(3-hexylthiophene) (P3HT), regio regular P3HT and soluble fullerene derivative, PCBM. By means of absorption, photoluminescence, atomic force microscopy and X-ray diffraction, we demonstrate that the structure of ternary films consists of crystallites of regular P3HT embedded into a random polymer matrix acting as a soft scaffolding where PCBM can only form nanoscale aggregates but cannot grow the detrimental micron-sized structures often observed in the conventional regular P3HT:PCBM case upon annealing. The ternary films exhibit higher degree of crystallinity than the conventional blends, but with smaller crystallite sizes. Moreover, we show that the addition of the random polymer chains does not prevent good charge carrier transport for regio random P3HT concentrations up to 50% of the total polymer content. Finally, we prove that solar cells based on the ternary systems have a similar short circuit current than the conventional binary, but improved open circuit current (by ~100 mV), which leads to an overall enhancement of power conversion efficiency.1133-1140
Xiao-Hong Zhang, Shree Prakash Tiwari, Bernard Kippelen. Pentacene organic field-effect transistors with polymeric dielectric interfaces: Performance and stability
Abstract:
Low-voltage pentacene organic field-effect transistors (OFETs) with different gate dielectric interfaces are studied and their performance in terms of electrical properties and operational stability is compared. Overall high electrical performance is demonstrated at low voltage by using a 100 nm-thick high-κ gate dielectric layer of aluminum oxide (Al₂O₃) fabricated by atomic layer deposition (ALD) and modified with hydroxyl-free low-j polymers like polystyrene (PS), divinyltetramethyldisiloxane-bis(benzocyclobutene) (BCB) (CycloteneTM, Dow Chemicals), and as well as with the widely used octadecyl-trichlorosilane (OTS). Devices with PS and BCB dielectric surfaces exhibit almost similar electrical performance with high field-effect mobilities, low subthreshold voltages, and high on/off current ratios. The higher mobility in pentacene transistors with PS can be correlated to the better structural ordering of pentacene films, as demonstrated by atomic force microscopy (AFM) images and X-ray diffraction (XRD). The devices with PS show good electrical stability under bias stress conditions (V_GS = V_DS = ~10 V for 1 h), resulting in a negligible drop (~2%) in saturation current (I_DS) in comparison to that in devices with OTS (~12%), and to a very high decay (~30%) for the devices with BCB.1141-1145
Lai-Wan Chong, Ying-Nien Chou, Yuh-Lang Lee, Ten-Chin Wena, Tzung-Fang Guo. Hole-injection enhancement of top-emissive polymer light-emitting diodes by P3HT/FNAB modification of Ag anode
Abstract:
Based on the hole-transport characteristic of poly(3-hexylthiophene) (P3HT), self-assembled thin layer of P3HT was employed to modify the Ag anode of a top-emissive polymer light-emitting diodes (T-PLEDs) to enhance the hole-injection from the Ag anode. The experimental results show that introduction of a P3HT thin layer significantly decreases the threshold voltage of a T-PLED. However, only slightly increase of the work function was achieved due to this modification. To increase the work function of the P3HT modified Ag anode (Ag/P3HT), 1-fluoro-2-nitro-4-azidobenzene (FNAB) was introduced into the terminal tail (–C₆H₁₃) of P3HT thin layer, which leads to a work function increment of 0,23 eV and a further enhancement in the hole-injection. The luminous efficiency achieved by this modified anode (Ag/P3HT/FNAB) is about fourfold higher than the efficiency obtained from the base device.1146-1151
Zhiwei Liu, Michael G. Helander, Zhibin Wang, Zhenghong Lu. Efficient single layer RGB phosphorescent organic light-emitting diodes
Abstract:
We report efficient single layer red, green, and blue (RGB) phosphorescent organic lightemitting diodes (OLEDs) using a ‘‘direct hole injection into and transport on triplet dopant strategy. In particular, red dopant tris(1-phenylisoquinoline)iridium [Ir(piq)₃], green dopant tris(2-phenylpyridine)iridium [Ir(ppy)₃], and blue dopant bis(3,5-difluoro-2-(2-pyridyl) phenyl-(2-carboxypyridyl)iridium [FIrpic] were doped into an electron transporting 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) host, respectively, to fabricate RGB single layer devices with indium tin oxide (ITO) anode and LiF/Al cathode. It is found that the maximum current efficiencies of the devices are 3,7, 34,5, and 6,8 cd/A, respectively. Moreover, by inserting a pure dopant buffer layer between the ITO anode and the emission layer, the efficiencies are improved to 4,9, 43,3, and 9,8 cd/A, respectively. It is worth noting that the current efficiency of the green simplified device was as high as 34,6 cd/A, even when the luminance was increased to 1000 cd/m2 at an extremely low applied voltage of only 4,3 V. A simple accelerated aging test on the green device also shows the lifetime decay of the simplified device is better than that of a traditional multilayered one.1152-1157
Kwang Hyup An, Brendan O’Connor, Kevin P. Pipe, Max Shtein. Organic photodetector with spectral response tunable across the visible spectrum by means of internal optical microcavity
Abstract:
We demonstrate an organic photodetector (OPD) structure in which the active layers and a thick optical spacer are sandwiched between two metallic electrodes, forming a Fabry–Perot resonant cavity. The second resonant mode of this cavity can be positioned by means of an optical spacer so that its maximum intensity overlaps with the donor–acceptor interface, leading to a peak in the external quantum efficiency (EQE) of the OPD for this resonant wavelength. The photoresponse can thus be tuned across the visible spectrum by adjusting the spacer thickness, while the full width half maximum remains approximately 50 nm. Because the active layers can be thin in this approach, the EQE is not sacrificed, and the device can achieve a relatively high response frequency that does not suffer from the inclusion of the optical spacer. We simulate the photoresponse of OPD structure using transfer matrix optical calculations and an exciton diffusion model; our simulation also explicitly accounts for interface roughness measured by atomic force microscopy. Angular dependence of the OPD’s response is also measured and discussed.1158-1162
Miao-Tsai Chu, Meng-Ting Lee, Chin H. Chen, Mei-Rurng Tseng. Improving the performance of blue phosphorescent organic light-emitting devices using a composite emitter
Abstract:
A composite emitter is constructed by doping a carrier-transporting material into a conventional emitter composing of only host and dopant. The transport of carriers from either hole- or electron-transporting layer into the emitter can be promoted through the carriertransporting material, in particular, when a wide-band-gap host material is used. A blue phosphorescent OLED based on iridium(III)bis((4,6-difluorophenyl)-pyridinate-N,C^2')-picolinate (FIrpic) as dopant in the composite emitter achieved a power efficiency of 20 μm/W and a low driving voltage of 4,2 V at 1000 cd/m2, whose current efficiency at 20 mA/cm² was 2,5 times better than that of device using the conventional emitter.1163-1169
Hyunsu Cho, Changhun Yun, Jae-Woo Park, Seunghyup Yoo. Highly flexible organic light-emitting diodes based on ZnS/Ag/WO₃ multilayer transparent electrodes
Abstract:
We report our study on highly flexible organic light-emitting diodes based on ZnS/Ag/WO₃ (ZAW) multilayer transparent electrodes in which high conductivity and ductility of Ag layers allow for efficient sheet conduction and flexibility while ZnS and WO₃ layers provide a means for enhancement in optical transmission and/or carrier-injection. Devices with ZAW anodes fabricated on planarized plastic substrates not only exhibit a performance and operational stability comparable to or better than those of ITO-based devices but also show a mechanical flexibility that is far superior to that of ITO-based devices. Experimental results show that a consistent performance can be obtained in ZAW-based devices upon repeated bending down to a radius of curvature of 5 mm, below which the flexibility of the devices is limited ultimately by the delamination occurring at cathode/organic interfaces rather than by the ZAW electrodes themselves.1170-1173
James W. Kingsley, Andrew J. Pearson, Lee Harris, Steven J. Weston, David G. Lidzey. Detecting 6 MV X-rays using an organic photovoltaic device
Abstract:
An organic photovoltaic (OPV) device has been used in conjunction with a flexible inorganic phosphor to produce a radiation tolerant, efficient and linear detector for 6 MV Xrays. The OPVs were based on a blend of poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C₆₁-butyric acid methyl ester (PCBM). We show that the devices have a sensitivity an order of magnitude higher than a commercial silicon detector used as a reference. Exposure to 360 Grays of radiation resulted in a small (2%) degradation in performance demonstrating that these detectors have the potential to be used as flexible, real-time, in vivo dosimeters for oncology treatments.1174-1177
Xiaoyang Guo, Fengmin Liu, Wei Yue, Zhiyuan Xie, Yanhou Geng, Lixiang Wang. Efficient tandem polymer photovoltaic cells with two subcells in parallel connection
Abstract:
Tandem polymer photovoltaic cells with the subcells having different absorption characteristics in series connection are widely investigated to enhance absorption coverage over the solar spectrum. Herein, we demonstrate efficient tandem polymer photovoltaic cells with the two stacked subcells comprising different band-gap conjugated polymer and fullerene derivative bulk heterojunction in parallel connection. A semitransparent metal layer combined with inorganic semiconductor compounds is utilized as the intermediate electrode of the two stacked subcells to create the required built-in potential for collecting photo-generated charges. The short-circuit current of the stacked cell is the sum of the subcells and the open-circuit voltage is similar to the subcells.1178-1181
Bonan Kang, L.W. Tan, S.R.P. Silva. Ultraviolet-illuminated fluoropolymer indium–tin-oxide buffer layers for improved power conversion in organic photovoltaics
Abstract:
We demonstrate that the charge carrier extraction in double heterojunction organic photovoltaic(OPV) devices can be enhanced by inserting an UV-illuminated fluoropolymer polytetrafluoroethylene(PTFE) layer between indium–tin-oxide and the thermal evaporated copper–phthalocyanine(CuPc)/buckyball(C₆₀) organic active layers. In this work, we show that the anode work function influences the photocarrier collection characteristics, where the short-circuit current and open-circuit voltage increase from 1,6 to 4,8 mA/cm² and 0,41 to 0,48 V, respectively after the buffer layer insertion associated primary with the barrier decrease in the ITO/CuPc interface. This result shows the potential of UV-illuminated PTFE as a low-cost stable buffer layer for OPV devices.1182-1186
Jason D. Myers, Teng-Kuan Tseng, Jiangeng Xue. Photocarrier behavior in organic heterojunction photovoltaic cells
Abstract:
We have investigated the bias dependence of photocurrent in several organic heterojunction cells to elucidate the behavior of photogenerated charge carriers. Both the planar and planar-mixed heterojunction devices are shown to always have negative photocurrent even at large forward biases; this phenomena has been attributed to an increased driving force for carrier diffusion away from the heterointerface as the applied bias increases. In contrast, the drift current generally dominates in mixed heterojunction devices due to distributed nature of charge generation throughout the active layer, leading to a photocurrent that is highly dependent on the internal electric field. This dependence gives rise to the reversal of the photocurrent direction at high biases when compared to that at the short-circuit condition. However, the voltage yielding zero photocurrent shows appreciable wavelength dependence, which is strongly correlated to the detailed charge carrier generation profile within the active layer.1187-1190
Matthieu Petit, Ryoma Hayakawa, Toyohiro Chikyow, Jonathan P. Hill, Katsuhiko Ariga, Yutaka Wakayama. Variable temperature characterization of N,N'-Bis(n-pentyl)terrylene-3,4:11,12-tetracarboxylic diimide thin film transistor
Abstract:
Organic thin film transistors (OTFT) based on N,N'-Bis(n-pentyl)terrylene-3,4:11,12-tetracarboxylic diimide (TTCDI-5C) with Al or Au top-contact electrodes were deposited on SiO₂ (200 nm)/p-Si (0 0 1) substrates. Carrier mobility was examined as a function of temperature in the range from 50 to 310 K. Two distinct carrier transfer behaviours were observed: temperature independent behaviour below 150 K and thermally activated behaviour above 150 K. Activation energies presented values of 85–130 meV depending on the metal electrodes (Au, Al), which can be attributed to the carrier traps at the interface and the energy-level offset between the lowest unoccupied molecular orbital (LUMO) and the work functions of the respective metals.1191-1194
Xinghua Liu, Zhuoyu Ji, Deyu Tu, Liwei Shang, Jiang Liu, Ming Liu, Changqing Xie. Organic nonpolar nonvolatile resistive switching in poly(3,4-ethylene-dioxythiophene): Polystyrenesulfonate thin film
Abstract:
In this paper, the reproducible nonpolar resistive switching is demonstrated in devices with the sandwiched structure of Au/poly(3,4-ethylene-dioxythiophene): polystyrenesulfonate/Au for nonvolatile memory application. The switching between high resistance state (OFF-state) and low resistance state (ON-state) does not depend on the polarity of the applied voltage bias, which is different from both the WORM characteristics and the bipolar switching characteristics reported before. The resistive ratio between the ON- and OFFstate is on the order of 10³ and increases with the device area decreasing. Both the ON- and OFF-state of the memory devices are stable, showing no significant degradation over 10⁴ s under continuous readout testing. It is proposed that the reduction and oxidation of PEDOT: PSS film might be the switching mechanism.1195-1199
Elias Said, Peter Andersson, Isak Engquist, Xavier Crispin, Magnus Berggren. Electrochromic display cells driven by an electrolyte-gated organic field-effect transistor
Abstract:
Monolithic integration of an organic field-effect transistor (OFET) and an organic electrochromic display cell operating at around 1 V is reported. This was achieved by utilising a common patterned layer of poly(styrenesulfonic acid) (PSSH). In the OFET, PSSH served as the electric double layer capacitors between the gate and the organic semiconductor channel. In the electrochromic pixel, PSSH was included as the electrolyte and transports protons from and to the electrochromic layer upon switching. The enhancement mode OFET enables a relatively faster updating speed, of the display cell, and provides a much simpler addressing and updating scheme as compared to smart pixels including a depletion mode electrochemical transistor.