Bar-coated high-performance organic thin-film transistors based on ultrathin PDFDT polymer with molecular weight independence

We report high-performance organic thin-film transistors (OTFTs) with an ultrathin active layer of difluorobenzothiadiazole-dithienosilole copolymer (PDFDT) form by using the wire bar-coating process. The top-gate/bottom contact (TG/BC) OTFTs based on bar-coated PDFDT polymer as channel material and poly(methyl methacrylate) (PMMA) as gate dielectric show a hole mobility of up to 2.2 cm² V⁻¹s⁻¹ with a current ON/OFF ratio (I_on/I_off) of 10⁴∼10⁵, with the mobility being two times larger than that of the spin-coated PDFDT based OTFTs. The higher mobility of the bar-coated PDFDT polymer films can be attributed to the well-organized fibril structures of the polymer chains. Importantly, two different molecular weight polymers (M_n = 23 and 34 kDa) were employed to conduct these experiments and both batches showed about the same performance, which mitigates the typical batch-to-batch variation in OTFT performance. Furthermore, we explored the operational stability of the bar-coated OTFTs in ambient air and nitrogen environments. The bias-stress and cycling tests between the ON/OFF states of the bar-coated devices showed high stability in both nitrogen and air. Conclusively, here we demonstrate that (i) a simple bar-coating process is a better method to control and obtain good polymer morphology in comparison to spin-coating, and (ii) the PDFDT polymer has great potential to provide good reproducibility and stability in large-area OTFT devices.     

Side chain engineering: The effect on the properties of isoindigo-based conjugated polymers contain different length and structure alkyl chains on nitrogen atom

A series of donor-acceptor (D-A) conjugated polymers based on benzo[1,2-b:4,5-b’]dithiophene (BDT) and isoindigo with different alkyl side chains were designed and synthesized. These polymers named PBDT-TT-IID_O, PBDT-TT-IID_EH, PBDT-TT-IID_BO, PBDT-TT-IID_HD, and PBDT-TT-IID_OD have different length or structure of the alkyl side chains on isoindigo unit. As the length of the alkyl chain increases, the solubility of the polymer enhances. The results indicate that the alkyl side chains have little effect on the optical properties of individual polymer molecules, but have a significant impact on optical, electrochemical, film-forming and photovoltaic properties of the polymers in the aggregated state. PBDT-TT-IID_HD with a sixteen carbon branched chain achieves the best power conversion efficiencies (PCEs) of 6.83% when blending with [6,6]-phenyl C71 butyric acid methyl ester (PC₇₁BM) as acceptor. The influence of the alkyl side chain on the short-circuit current is much greater than that of the open circuit voltage. Atomic force microscopy (AFM) reveals that the side chains changed the morphology of the active layers and the size of the phase region. For isoindigo based polymers, hexyl-decyl group in the commonly used alkyl chains appear to be a good choice.     

Impact of alkyl chain length of 1,n-diiodoalkanes on PC71BM distribution in both bulk and air surface of PTB7:PC71BM film

The impact of alkyl chain length of different additives, such as 1,4-diiodobutane (DIB), 1,6-diiodohexane (DIH), 1,8-diiodooctane (DIO) and 1,10-diiododecane (DID), on the PC₇₁BM distribution in PTB7:PC₇₁BM-based polymer solar cells, is systematically investigated, for the first time. Among these additives, DIO is found to have the optimum alkyl chain length that maximizes the performance of PTB7:PC₇₁BM based polymer solar cells, attaining a power conversion efficiency as high as 8.84%, which is almost four times higher than that without any additives. For DID additives (longer alkyl chain length than DIO), a drop in efficiency to 7.91% was observed. Experimental investigations show that the microstructure of the bulk and the surface layer as well as the surface morphology of the PTB7:PC₇₁BM polymer film can be controlled simultaneously by varying the alkyl chain length of additives. Results also show that the substantial improvement in performance is attributed to the improved 1) phase segregation, 2) PC₇₁BM distribution uniformity in the bulk of the PTB7:PC₇₁BM film, 3) surface smoothness and 4) high PTB7 content at the interface between the active layer and the top electrode.     

Effects of incorporating salts with various alkyl chain lengths on carrier balance of light-emitting electrochemical cells

Recently, solid-state light-emitting electrochemical cells (LECs) have attracted much attention since they have advantages such as low operation voltages, simple device structure and balanced carrier injection. Salts are commonly added in the emissive layer of LECs to provide additional mobile ions and thus to accelerate device response. However, in addition to modified ionic property, carrier balance of LECs would also be tailored by salt additives. In this work, we improve device efficiency of LECs by incorporating imidazole-based salts bearing various alkyl chain lengths. As the alkyl chain length of the added salt increases, the device current decreases and the recombination zone approaches the anode. These results reveal that hole transport in the emissive layer of LEC containing a salt with a larger size would be impeded more significantly than electron transport. When doped with a salt possessing a proper size, nearly doubled device efficiency as compared to that of the neat-film device can be obtained due to improved carrier balance. This work demonstrates a feasible strategy to improve device performance of LECs and clarifies the physical insights of the effect of salt size on carrier balance of LECs.     

White light-emitting devices based on star-shape like polymers with diarylmaleimde fluorophores on the side chain of polyfluorene arms

A series of novel star-shape like white polymers were synthesized by employing the benzene as the core, and incorporating different amount of bis (4-methoxyphenyl) maleimide guest onto the side-chain of the polyfluorene (PF) arm host. Due to the large feed ratio of core, such a construction strategy could efficiently avoid or suppress the formation of linear PF which always existed in the previous star-like polymers employing guest as core. When applied to the single emitting layer devices fabricated by solution spin-coating method, the efficiency of the devices enhanced gradually with the amount of guest increasing from 0.01% to 2%. The device performance was further improved substantially by annealing at 140 °C. A typical device base on P1 containing 1% dopant exhibited maximal luminous efficiency of 6.13 cd/A. Interestingly, the increase of efficiency is not originated from the self-dopant effect of α or β crystalline phase, which was always produced by thermal treatment at 120 °C in linear or previous star-like polyfluorenes. Morphology analysis disclosed that annealing made the polymeric molecules stack become closer, consequently resulting in a more effectively charge transfer and energy transfer from host to guest. As a result, the compact molecular stacking of the star-shape like polymers should be responsive for the high efficiency of annealed devices. The results would be conducive to design new star-shape like polymers with more arms, and improve the performance of white devices.     

Effect of doping with nitrogen on electrical properties and erbium electroluminescence of a-Si:H(Er) films

The effect of nitrogen doping on the electrical and electroluminescence properties of amorphous hydrogenated silicon films doped with erbium has been studied. The parameters of the material, the characteristics of structures on its base, and the efficiency of Er electroluminescence (λ=1.54 μm) are determined by the excess of the nitrogen doping level over the background value depending on the Er concentration. It is shown that effectively luminescing structures can be obtained by reducing the background concentration, with nitrogen doping remaining at the level of ∼10²¹ cm⁻³. A possible mechanism is proposed, accounting for this effect in terms of two possible forms of nitrogen incorporation into an Er-doped a-Si:H structure: with either an Er-N complex or a Na ₄ ⁺ -Si ₃ ⁻ charged defect pair formed. In this case, the electroluminescence efficiency is determined by the number of these pairs. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 10, 2001, pp. 1250–1255. Original Russian Text Copyright ? 2001 by Kon’kov, Terukov, Granitsyna.     

In situ deposition of polythiophene nanoparticles on flexible transparent films: Effect of the process conditions

Polythiophene (PTh) was deposited as a thin film and nanoparticles on polyethylene naphthalate (PEN) films via ultrasonication or via magnetic stirring with or without a cationic (cetyltrimethylammonium bromide, CTAB) or non-ionic (Triton X-100) surfactant. The resulting conductive flexible films were characterized by UV-Vis spectroscopy, fluorescence spectrometry, field-emission scanning electron microscopy, contact angle measurements, the four-point-probe technique, X-ray diffraction, and cyclic voltammetry. The highest conductivity was obtained for PTh-CTAB nanoparticles, which had the most compact surface morphology among nanoparticles on PEN films. In general, the surface morphology, electrical conductivity, and whether PTh nanoparticles had been precipitated or deposited depended on the surfactant used, the surfactant/monomer ratio, the oxidant/monomer ratio, and the monomer concentration.     

Effect of Immobilized Nerve Growth Factor on Conductive Polymers: Electrical Properties and Cellular Response

The use of biologically active dopants in conductive polymers allows the polymer to be tailored for specific applications. The incorporation of nerve growth factor (NGF) as a co‐dopant in the electrochemical deposition of conductive polymers is evaluated for its ability to elicit specific biological interactions with neurons. The electrochemical properties of the NGF‐modified conducting polymers are studied by impedance spectroscopy and cyclic voltammetry. Impedance measurements at the neurobiologically important frequency of 1 kHz reveal that the minimum impedance of the NGF‐modified polypyrrole (PPy) film, 15 kΩ, is lower than the minimum impedance of peptide‐modified PPy film (360 kΩ). Similar results are found with NGF‐modified poly(3,4‐ethylene dioxythiophene) (PEDOT). The microstructure of the conductive polymer films is characterized by optical microscopy and electron microscopy and indicates that the NGF‐functionalized polymer surface topology is similar to that of the unmodified polymer film. Optical and fluorescence microscopy reveal that PC‐12 (rat pheochromacytoma) cells adhered to the NGF‐modified substrate and extended neurites on both PPy and PEDOT, indicating that the NGF in the polymer film is biologically active. Taken together these data indicate that the incorporation of NGF can modify the biological interactions of the electrode without compromising the conductive properties or the morphology of the polymeric film.     

Nd3+掺杂浓度对无水冷Nd:YAG激光器输出特性的影响

无水冷Nd:YAG激光器采用一种双拱形激光二极管阵列对双棒串接的Nd:YAG进行同心泵浦,将双拱形激光二极管面阵发出的光作高斯光束处理,利用高斯光束通过光学系统的变换规律,借助计算机模拟,研究了钕离子掺杂浓度对LD泵浦的无水冷Nd:YAG激光器的荧光分布、激光建立时间、输出能量及脉宽等输出特性的影响.搭建双半环形LDA侧面泵浦的低频无水冷电光调O Nd:YAG激光器的实验平台,对Nd3+掺杂浓度分别为1%、0.8%、0.6%的激光晶体进行实验测试,给出了LD泵浦的无水冷Nd:YAG激光器的Nd3+掺杂浓度与激光建立时间、输出能量、脉宽等参量的定量关系曲线,实验结果与理论分析结果基本相符.     

Effect of a novel self-assembly based on coordination polymer with zinc porphyrin in supramolecular solar cells

Within this work, we firstly report the self-assemblies of zinc porphyrin coordination polymers (CPs) appended isonicotinic acid ligands by metal–ligand axial coordination approach immobilized on the nanostructured TiO₂ electrode surfaces in photoelectrochemical devices. Compared to the assemblies based on zinc porphyrins integrated isonicotinic acid ligands via metal–ligand axial coordination or metal–ligand edged binding approach, the CPs-based assemblies exhibit significantly improved photovoltaic performances. Especially, the assembly based on iminazole-substituted zinc porphyrin coordination polymer exhibits an excellent photovoltaic performance with a short circuit photocurrent density (J_sc) of 3.8 mA cm⁻², an open circuit voltage (V_oc) of 0.31 V, a fill factor (FF) of 0.67 and an overall conversion efficiency (η) of 0.48% under AM 1.5 conditions. The results serve as another good testing ground for the fabrication of supramolecular devices techniques in future.     

Solid Polymer Electrolytes Based on Ionic Graft Polymers: Effect of Graft Chain Length on Nano‐Structured,Ionic Networks

The length of graft chains in graft polymers is controlled in order to dictate the formation of a nanochannel network of ions in a non‐ionic matrix. Graft polymers were prepared by copolymerization of styrene with poly(sodium styrene sulfonate) (PSSNa) macromonomers. The latter were prepared with controlled molecular weight and narrow polydispersity by stable free radical polymerization. Phase separation of ionic aggregates occurs to a greater extent in films prepared from amphiphilic polymers possessing longer graft chains. Films prepared from polymers containing low ion content comprise of isolated ionic domains and exhibit low ionic conductivity. Increasing the ion content with the membrane, by increasing the number density of ionic graft chains in the polymer, results in ionic domains that coalesce into a network of nanochannels, and a dramatic increase in ion conductivity is observed. The ionic network is developed to a greater extent for films based on longer ionic graft chain polymers; an observation explained on the basis of phase separation.     

A Versatile Method to Fabricate Highly In‐Plane Aligned Conducting Polymer Films with Anisotropic Charge Transport and Thermoelectric Properties: The Key Role of Alkyl Side Chain Layers on the Doping Mechanism

A general method is proposed to produce oriented and highly crystalline conducting polymer layers. It combines the controlled orientation/crystallization of polymer films by high‐temperature rubbing with a soft‐doping method based on spin‐coating a solution of dopants in an orthogonal solvent. Doping rubbed films of regioregular poly(3‐alkylthiophene)s and poly(2,5‐bis(3‐dodecylthiophen‐2‐yl)thieno[3,2‐b ]thiophene) with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄TCNQ) yields highly oriented conducting polymer films that display polarized UV–visible–near‐infrared (NIR) absorption, anisotropy in charge transport, and thermoelectric properties. Transmission electron microscopy and polarized UV–vis–NIR spectroscopy help understand and clarify the structure of the films and the doping mechanism. F₄TCNQ^? anions are incorporated into the layers of side chains and orient with their long molecular axis perpendicular to the polymer chains. The ordering of dopant molecules depends closely on the length and packing of the alkyl side chains. Increasing the dopant concentration results in a continuous variation of unit cell parameters of the doped phase. The high orientation results in anisotropic charge conductivity (σ) and thermoelectric properties that are both enhanced in the direction of the polymer chains (σ = 22 ± 5 S cm^?1 and S = 60 ± 2 µV K^?1). The method of fabrication of such highly oriented conducting polymer films is versatile and is applicable to a large palette of semiconducting polymers.     

Polymorphism in Crystalline Microfibers of Achiral Octithiophene: The Effect on Charge Transport,Supramolecular Chirality and Optical Properties

Polymorphic crystalline microfibers from an achiral octithiophene with one S‐hexyl substituent per ring are separately and reproducibly grown with the same characteristics on various solid surfaces, including the interdigitated electrodes/SiO₂ surface of a bottomcontact field‐effect transistor. The arrangement of the same molecule in two diverse supramolecular structures leads to markedly different electronic, optical, and charge mobility properties. The microfibers—straight and yellow emitting or helical and red emitting—exhibit p‐type charge transport characteristics, with the yellow ones showing a charge mobility and on/off current ratio of one and three orders of magnitude, respectively, greater than the red ones. Both forms show circular dichroism signals with significant differences from one form to the other. DFT calculations show that the octithiophene exists in two different quasi‐equienergetic conformations aggregating with diverse orientations of the substituents. This result suggests that the observed polymorphism is conformational in nature. The self‐assembly, driven by sulfur–sulfur non‐bonding interactions, amplifies the small property differences between conformers, leading to quite different bulk properties.     

Conjugated Polymer Based on Polycyclic Aromatics for Bulk Heterojunction Organic Solar Cells: A Case Study of Quadrathienonaphthalene Polymers with 2% Efficiency

Polycyclic aromatics offer great flexibility in tuning the energy levels and bandgaps of resulting conjugated polymers. These features have been exploited in the recent examples of benzo[2,1‐b:3,4‐b']dithiophene ( BDT )‐based polymers for bulk heterojunction (BHJ) photovoltaics (ACS Appl. Mater. Interfaces 2009 , 1, 1613). Taking one step further, a simple oxidative photocyclization is used here to convert the BDT with two pendent thiophene units into an enlarged planar polycyclic aromatic ring— q uadra t hieno n aphthalene ( QTN ). The reduced steric hindrance and more planar structure promotes the intermolecular interaction of QTN‐ based polymers, leading to increased hole mobility in related polymers. As‐synthesized homopolymer ( HMPQTN ) and donor–acceptor polymer ( PQTN ‐ BT ) maintain a low highest occupied molecular orbital (HOMO) energy level, ascribable to the polycyclic aromatic ( QTN ) moiety, which leads to a good open‐circuit voltage in BHJ devices of these polymers blended with PCBM ([6,6]‐phenyl‐C₆₁‐butyric acid methyl ester; HMPQTN : 0.76 V, PQTN ‐ BT : 0.72 V). The donor–acceptor polymer ( PQTN ‐ BT ) has a smaller optical bandgap (1.6 eV) than that of HMPQTN (2.0 eV), which explains its current (5.69 mA cm^?2) being slightly higher than that of HMPQTN (5.02 mA cm^?2). Overall efficiencies over 2% are achieved for BHJ devices fabricated from either polymer with PCBM as the acceptor.     

Effect of deposition conditions on charging processes in SiNx: Application to RF-MEMS capacitive switches

The paper presents a systematic investigation of dielectric charging in low temperature silicon nitride for RF-MEMS capacitive switches. The dielectric charging is investigated with the aid of Metal-Insulator-Metal (MIM) capacitors with different thickness dielectric film and symmetric and asymmetric metal contacts. The experimental results demonstrate that the charging process is almost symmetric in low temperature deposited silicon nitride. Experiments performed in both MIM and MEMS reveal that the charging process is strongly affected by temperature. Specifically at high temperatures the charging rate increases exponentially with temperature.     

Effect of electronic flame off parameters on copper bonding wire: Free-air ball deformability, heat affected zone length, heat affected zone breaking force

Cu bonding wire is more and more used for interconnections to integrated circuits (ICs) to reduce cost and increase performance compared to Au wire. To eliminate underpad damage for Cu wire applications, it is worthwhile to reduce the hardness of the free-air ball (FAB). Short heat affected zone (HAZ) and high HAZ breaking load are often required for advanced microelectronics packaging in order to decrease the loop height and thereby the package thickness.Online measurements of deformability and HAZ breaking force at temperatures close to the bonding temperature of 220 °C are new tools used in this study to evaluate the effects of electronic flame off (EFO) current and firing time on the Cu FAB deformability and the HAZ length and tensile strength. FABs with 50 μm diameter formed from a 25 μm diameter Cu wire with a breaking load of 118.6 mN were used. EFO currents and firing times ranged from 40 to 250 mA and 0.11 to 0.90 ms, respectively. Average FAB deformability factors, HAZ breaking forces, and HAZ lengths were in the rounded ranges of 36.64–44.09% (with a deformation force of 0.60 N), 107.7–116.8 mN, and 167–215 μm, respectively. When produced with 250 mA current during 0.11 ms, the FABs are 7.01–7.89% more deformable than when produced with 45 mA during 0.9 ms, the HAZ breaking force is 7.53–9.37% higher, and the HAZ length is 7–90 μm shorter.     

偏心度对矩形截面Nd:GdVO4晶体热效应的影响

对激光二极管（LD）端面高功率偏心抽运矩形截面激光晶体引起的热效应进行了研究。建立了符合实际的热模型,利用一种新的解析方法得出了矩形截面激光晶体温度场以及热形变场的通解形式。定义了偏心抽运矩形截面偏心度（ERS）,得出了ERS对激光晶体内部温度场及热形变场影响的规律。研究表明：随着ERS的增加,激光晶体最高温升及最大热形变随之移动并降低;当ERS分为0．50、0．75时,Nd：GdVO4晶体的最高升温相对中心抽运分别下降了3．3％、12．2％,最大热形变量相对中心抽运分别下降了8．8％、27．4％。