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1.
We measure the potential profiles of both dynamic and fixed junction planar light-emitting electrochemical cells (LECs) using Scanning Kelvin Probe Microscopy (SKPM) and compare the results against models of LEC operation. We find that, in conventional dynamic junction LECs formed using lithium trifluoromethanesulfonate (LiTf), poly(ethylene oxide) (PEO), and the soluble alkoxy-PPV derivative poly[2-methoxy-5-(3',7'-dimethyl-octyloxy)-p-phenylenevinylene (MDMO-PPV), the majority (>90%) of the potential is dropped near the cathode with little potential drop across either the film or the anode/polymer interface. In contrast, when examining fixed junction LECs where the LiTf is replaced with [2-(methacryloyloxy)ethyl] trimethylammonium 2-(methacryloyloxy)ethane-sulfonate (METMA/MES), the potential is dropped at both contacts during the initial poling. The potential profile evolves over a period of approximately 60 min under bias to achieve a final profile similar to that obtained in the LiTf systems. In addition to elucidating the differences between conventional dynamic LECs and fixed LECs incorporating cross-linkable ion pair monomers, the results on both systems provide direct evidence for a primarily "p-type" LEC consistent with the emitting junction near the cathode and relatively small electric fields across the bulk of the device for these two material systems.  相似文献   

2.
李永舫 《电化学》2005,11(1):1-7
简要介绍本研究组 1997年以来在聚合物发光电化学池 (LEC)研究中取得的一些成果,包括发光聚合物的电化学性质及其HOMO和LUMO能级的电化学测量,LECp i n结的交流阻抗分析,双功能嵌段共聚物LEC,以及咪唑盐离子液体掺杂的室温准冷冻p i n结LEC等.  相似文献   

3.
We report phosphorescent sensitized fluorescent near-infrared (NIR) light-emitting electrochemical cells (LECs) utilizing a phosphorescent cationic transition metal complex [Ir(ppy)(2)(dasb)](+)(PF(6)(-)) (where ppy is 2-phenylpyridine and dasb is 4,5-diaza-9,9'-spirobifluorene) as the host and two fluorescent ionic NIR emitting dyes 3,3'-diethyl-2,2'-oxathiacarbocyanine iodide (DOTCI) and 3,3'-diethylthiatricarbocyanine iodide (DTTCI) as the guests. Photoluminescence measurements show that the host-guest films containing low guest concentrations effectively quench host emission due to efficient host-guest energy transfer. Electroluminescence (EL) measurements reveal that the EL spectra of the NIR LECs doped with DOTCI and DTTCI center at ca. 730 and 810 nm, respectively. Moreover, the DOTCI and DTTCI doped NIR LECs achieve peak EQE (power efficiency) up to 0.80% (5.65 mW W(-1)) and 1.24% (7.84 mW W(-1)), respectively. The device efficiencies achieved are among the highest reported for NIR LECs and thus confirm that phosphorescent sensitized fluorescence is useful for achieving efficient NIR LECs.  相似文献   

4.
We demonstrate that electrochemical side-reactions involving the electrolyte can be a significant and undesired feature in light-emitting electrochemical cells (LECs). By direct optical probing of planar LECs, comprising Au electrodes and an active material mixture of {poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) + poly(ethylene oxide) (PEO) + KCF3SO3}, we show that two direct consequences of such a side-reaction are the appearance of a "degradation layer" at the negative cathode and the formation of the light-emitting p-n junction in close proximity to the cathode. We further demonstrate that a high initial drive voltage and a high ionic conductivity of the active material strongly alleviate the extent of the side reaction, as evidenced by the formation of a relatively centered p-n junction, and also rationalize our findings in the framework of a general electrochemical model. Finally, we show that the doping concentrations in the doped regions at the time of the p-n junction formation are independent of the applied voltage and relatively balanced at approximately 0.11 dopants/MEH-PPV repeat unit in the p-type region and approximately 0.15 dopants/MEH-PPV repeat unit in the n-type region.  相似文献   

5.
Solid-state light-emitting electrochemical cells (LECs) have several advantages, such as low-voltage operation, compatibility with inert metal electrodes, large-area flexible substrates, and simple solution-processable device architectures. However, most of the studies on saturated red LECs show low or moderate device efficiencies (external quantum efficiency (EQE) <3.3 %). In this work, we demonstrate a series of five red-emitting cationic iridium complexes ( RED1- - RED5 ) with 2,2′-biquinoline ligands and test their electroluminescence (EL) characteristics in LECs. The Commission Internationale de l′Eclairage (CIE) 1931 coordinates for the LECs based on these complexes are all beyond the National Television System Committee (NTSC) red standard point (0.67, 0.33). The maximal EQE of the neat-film RED1 -based LECs reaches 7.4 %. The reddest complex, RED3 , is doped in the blue-emitting host complex, BG , to fabricate host–guest LECs. The maximal EQE of the host–guest LECs (1 wt % complex RED3 ) reaches 9.4 %, which is among the highest reported for the saturated red LECs.  相似文献   

6.
The formation of advanced glycation end products (AGEs) has been considered to be a potential causative factor of injury to lens epithelial cells (LECs). Damage of LECs is believed to contribute to cataract formation. The purpose of this study was to investigate the cytotoxic effect of AGEs on LECs both in vitro and in vivo. We examined the accumulation of argpyrimidine, a methylglyoxal-derived AGE, and the expression of apoptosis-related molecules including nuclear factor- kappaB (NF-κB), Bax, and Bcl-2 in the human LEC line HLE-B3 and in cataractous lenses of Zucker diabetic fatty (ZDF) rats, an animal model of type 2 diabetes. In cataractous lenses from twenty-oneweek- old ZDF rats, LEC apoptosis was markedly increased, and the accumulation of argpyrimidine as well as subsequent activation of NF-κB in LECs were significantly enhanced. The ratio of Bax to Bcl-2 protein levels was also increased. In addition, the accumulation of argpyrimidine triggered apoptosis in methylglyoxal- treated HLE-B3 cells. However, the presence of pyridoxamine (an AGEs inhibitor) and pyrrolidine dithiocarbamate (a NF-κB inhibitor) prevented apoptosis in HLE-B3 cells through the inhibition of argpyrimidine formation and the blockage of NF-κB nuclear translocalization, respectively. These results suggest that the cellular accumulation of argpyrimidine in LECs is NF-κB-dependent and pro-apoptotic.  相似文献   

7.
We study the influence of the carrier injection efficiency on the performance of light-emitting electrochemical cells (LECs) based on a hole-preferred transporting cationic transition metal complex (CTMC) [Ir(dfppz)(2)(dtb-bpy)](+)(PF(6)(-)) (complex 1) and an electron-preferred transporting CTMC [Ir(ppy)(2)(dasb)](+)(PF(6)(-)) (complex 2) (where dfppz is 1-(2,4-difluorophenyl) pyrazole, dtb-bpy is 4,4'-di(tert-butyl)-2,2'-bipyridine, ppy is 2-phenylpyridine and dasb is 4,5-diaza-9,9'-spirobifluorene). Experimental results show that even with electrochemically doped layers, the ohmic contacts for carrier injection could be formed only when the carrier injection barriers were relatively low. Thus, adding carrier injection layers in LECs with relatively high carrier injection barriers would affect carrier balance and thus would result in altered device efficiency. Comparison of the device characteristics of LECs based on complex 1 and 2 in various device structures suggests that the carrier injection efficiency of CTMC-based LECs should be modified according to the carrier transporting characteristics of CTMCs to optimize device efficiency. Hole-preferred transporting CTMCs should be combined with an LEC structure with a relatively high electron injection efficiency, while a relatively high hole injection efficiency would be required for LECs based on electron-preferred transporting CTMCs. Since the tailored carrier injection efficiency compensates for the unbalanced carrier transporting properties of the emissive layer, the carrier recombination zone would be located near the center of the emissive layer and exciton quenching near the electrodes would be significantly mitigated, rendering an improved device efficiency approaching the upper limit expected from the photoluminescence quantum yield of the emissive layer and the optical outcoupling efficiency from a typical layered light-emitting device structure.  相似文献   

8.
Solid-state near-infrared (NIR) light-emitting devices have recently received considerable attention as NIR light sources that can penetrate deep into human tissue and are suitable for bioimaging and labeling. In addition, solid-state NIR light-emitting electrochemical cells (LECs) have shown several promising advantages over NIR organic light-emitting devices (OLEDs). However, among the reported NIR LECs based on ionic transition-metal complexes (iTMCs), there is currently no iridium-based LEC that displays NIR electroluminescence (EL) peaks near to or above 800 nm. In this report we demonstrate a simple method for adjusting the energy gap between the highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO) of iridium-based iTMCs to generate NIR emission. We describe a series of novel ionic iridium complexes with very small energy gaps, namely NIR1 – NIR6 , in which 2,3-diphenylbenzo[g]quinoxaline moieties mainly take charge of the HOMO energy levels and 2,2′-biquinoline, 2-(quinolin-2-yl)quinazoline, and 2,2′-bibenzo[d]thiazole moieties mainly control the LUMO energy levels. All the complexes exhibited NIR phosphorescence, with emission maxima up to 850 nm, and have been applied as components in LECs, showing a maximum external quantum efficiency (EQE) of 0.05 % in the EL devices. By using a host–guest emissive system, with the iridium complex RED as the host and the complex NIR3 or NIR6 as guest, the highest EQE of the LECs can be further enhanced to above 0.1 %.  相似文献   

9.
We report a significant decrease in turn‐on times of light‐emitting electrochemical cells (LECs) by tethering imidazolium moieties onto a cationic Ir complex. The introduction of two imidazolium groups at the ends of the two alkyl side chains of [Ir(ppy)2(dC6‐daf)]+(PF6)? (ppy=2‐phenylpyridine, dC6‐daf=9,9′‐dihexyl‐4,5‐diazafluorene) gave the complex [Ir(ppy)2(dC6MIM‐daf)]3+[(PF6)?]3 (dC6MIM‐daf=9,9‐bis[6‐(3‐methylimidazolium)hexyl]‐1‐yl‐4,5‐diazafluorene). Both complexes exhibited similar photoluminescent/electrochemical properties and comparable electroluminescent efficiencies. The turn‐on times of the LECs based on the latter complex, however, were much lower than those of devices based on the former. The improvement is ascribed to increased concentrations of mobile counterions ((PF6)?) in the neat films and a consequent increase in neat‐film ionic conductivity. These results demonstrate that the technique is useful for molecular modifications of ionic transition‐metal complexes (ITMCs) to improve the turn‐on times of LECs and to realize single‐component ITMC LECs compatible with simple driving schemes.  相似文献   

10.
We report efficient host-guest solid-state light-emitting electrochemical cells (LECs) utilizing a cationic terfluorene derivative as the host and a red-emitting cationic transition metal complex as the guest. Carrier trapping induced by the energy offset in the lowest unoccupied molecular orbital (LUMO) levels between the host and the guest impedes electron transport in the host-guest films and thus improves the balance of carrier mobilities of the host films intrinsically exhibiting electron preferred transporting characteristics. Photoluminescence measurements show efficient energy transfer in this host-guest system and thus ensure predominant guest emission at low guest concentrations, rendering significantly reduced self-quenching of guest molecules. EL measurements show that the peak EQE (power efficiency) of the host-guest LECs reaches 3.62% (7.36 lm W(-1)), which approaches the upper limit that one would expect from the photoluminescence quantum yield of the emissive layer (~0.2) and an optical out-coupling efficiency of ~20% and consequently indicates superior balance of carrier mobilities in such a host-guest emissive layer. These results are among the highest reported for red-emitting LECs and thus confirm that in addition to reducing self-quenching of guest molecules, the strategy of utilizing a carrier transporting host doped with a proper carrier trapping guest would improve balance of carrier mobilities in the host-guest emissive layer, offering an effective approach for optimizing device efficiencies of LECs.  相似文献   

11.
Light-emitting electrochemical cells(LECs) are organic photonic devices based on a mixed electronic and ionic conductor.The active layer of a polymer-based LEC consists of a luminescent polymer,an ion-solvating/transport polymer,and a compatible salt.The LEC p-n or p-i-n junction is ultimately responsible for the LEC performance.The LEC junction,however,is still poorly understood due to the difficulties of characterizing a dynamic-junction LEC.In this paper,we present an experimental and modeling study of the LEC junction using scanning optical imaging techniques.Planar LECs with an interelectrode spacing of 560μm have been fabricated,activated,frozen and scanned using a focused laser beam.The optical-beam-induced-current(OBIC)and photoluminescence(PL) data have been recorded as a function of beam location.The OBIC profile has been simulated in COMSOL that allowed for the determination of the doping concentration and the depletion width of the LEC junction.  相似文献   

12.
A new cationic iridium complex has been developed with 2-(1-phenyl-1H-pyrazol-3-yl)pyridine as the ancillary ligand, which bears a pendant protective phenyl ring within the molecule; blue-green light-emitting electrochemical cells (LECs) based on the complex show dramatically enhanced stability compared to the LEC based on a similar complex without pendant phenyl rings.  相似文献   

13.
We report a dynamic polymerization system based on the reversible nucleophilic Michael polyaddition of activated alkynes and dithiols. Four poly(dithioacetal)s(P1-P4) were prepared via the base-catalyzed thiol-yne "click" polyaddition of two dithiols(1,4-butanedithiol(4 S) and 1,5-pentanedithiol(5 S)) and two alkynones(3-butyn-2-one(Y1) and 1-phenyl-2-propyn-1-one(Y2)) at high concentrations. We systematically investigated the base-catalyzed polymerization of 4 S and Y1(for polymer P1) under different conditions, and found that this polymerization was a highly concentration-dependent dynamic system: polymer P1 was formed at high concentration, while seven-membered dithioacetal, 1-(1,3-dithiepan-2-yl) propan-2-one(C1), was obtained at low concentration. The polymerization of 4 S and Y2(for polymer P4)displayed similar polymerization behavior, generating 2-(1,3-dithiepan-2-yl)-1-phenylethanone(C4) at low concentration. On the contrary,polymer P2(from Y1 and 5 S) was exclusively obtained with no formation of eight-membered dithioacetal. The polymerizations of Y1 with 1,2-ethanedithiol(2 S) and 1,3-dimercaptopropane(3 S) only afforded corresponding five-and six-membered dithioacetals, 1-(1,3-dithiolan-2-yl)propan-2-one(C2) and 1-(1,3-dithian-2-yl) propan-2-one(C3). This dynamic behavior of P1 and P4 was attributed to the concentrationdependent retro-Michael addition reaction between a thiol and a β-sulfido-α,β-unsaturated carbonyl compound catalyzed by bases.Furthermore, polymers P1 and P4 could be depolymerized into C1 and C4 in yields of 58% and 95%, respectively. The ring-opening polymerization of C1 at high concentration could successfully regenerate polymer P1. Thus, a new type of closed-loop recyclable poly(dithioacetal)s was developed.  相似文献   

14.
Light-emitting electrochemical cells (LECs) are a promising type of electroluminescent device for display and lighting applications. In this study, LECs based on ionic iridium complexes utilizing a tetrazole based ancillary ligand were fabricated and their electrical properties were investigated. Two new iridium(III) complexes with tetrazole based ancillary ligands, namely, [Ir(ppy)2(tetrazole)]PF6 (complex 1) and [Ir(dfppy)2(tetrazole)]PF6 (complex 2) (where ppy is 2-phenylpyridine, dfppy is 2-(2,4-difluorophenyl)pyridine, tetrazole is 5-bromo-2-(2-methyl-2H-tetrazol-5-yl)-pyridine and PF6 is hexafluorophosphate), have been synthesized and characterized. These synthesized complexes were used for the fabrication of LEC devices. LECs based on complex 1 result in orange light emission (576 nm) with the Commission Internationale de l’Eclairage (CIE) coordinates of (0.45, 0.49), while complex 2 emits green (518 nm) electroluminescence with the CIE coordinates of (0.33, 0.49). Our work suggests that the light emission of cationic iridium complexes can easily be tuned by the substituents on the cyclometalated ligands.  相似文献   

15.
We present a study of photoinduced interfacial electron transfer (ET) dynamics of SnO2 nanocrystalline thin films sensitized by polythiophene derivatives (regioregular poly(3-hexylthiophene) (P3HT) and regiorandom poly(3-undecyl-2,2'-bithiophene) (P3UBT)). ET dynamics were measured by following the dynamics of injected electrons in SnO2 and polarons in the conjugated polymer using ultrafast mid-IR transient absorption spectroscopy. The rate of electron transfer from P3HT and P3UBT to SnO2 films was determined to occur on sub-picosecond time scale (120 +/- 20 fs). In P3HT/SnO2 composite, interchain charge transfer was found to compete with and reduce the quantum efficiency of interfacial electron transfer at high polymer loading. This interchain charge separation processes can be reduced in non-regioregular polymer or at low polymer loading levels.  相似文献   

16.
In all-polymer solar cells (APSCs),number-average molecular weights (Mns) of polymer donors and polymer acceptors play an important role in active layer morphology and photovoltaic performance.In this work,based on a series of APSCs with power conversion efficiency of approaching 10%,we study the effect of Mns of both polymer donor and polymer acceptor on active layer morphology and photovoltaic performance of APSCs.We select poly[4-(5-(4,8-bis(5-((2-butyloctyl)thio)thiophen-2-yl)-6-methylbenzo[1,2-b:4,5-b']dithiophen-2-yl)thiophen-2-yl)-5,6-difluoro-2-(2-hexyldecyl)-7-(5-methylthiophen-2-yl)-2H-benzo[d][1,2,3]triazole](CD1) as the polymer donor and poly[4-(5-(5,10-bis(2-dodecylhexadecyl)-4,4,g,9-tetrafluuoro-7-methyl-4,5,9,10-tetrahydro3a,5,8,10-tetraaza-4,g-diborapyren-2-yl)thiophen-2-yl)-7-(5-methylthiophen-2-yl)benzo[c][1,2,5]thiadiazole](PBN-14) as the polymer acceptor.The Mns of polymer donor CD1 are 14.0,35.5 and 56.1 kg/mol,respectively,and the Mns of polymer acceptor PBN-14 are 32.7,72.4 and 103.4 kg/mol,respectively.To get the desired biscontinueous fibrous network morphololgy of the polymer donor/polymer acceptor blends,at least one polymer should have high or medium Mn.Moreover,when the Mn of polymer acceptor is high,the active layer morphology and APSC device performance are insensitive to the Mn of polymer donor.The optimal APSC device performance is obtained when the Mn of both the polymer donor and the polymer acceptor are medium.These results provide a comprehensive and deep understanding on the interplay and the effect of Mn of polymer donors and polymer acceptors in high-performance APSCs.  相似文献   

17.
White electroluminescent (EL) emission from single-layered solid-state light-emitting electrochemical cells (LECs) based on host-guest cationic iridium complexes has been successfully demonstrated. The devices show white EL spectra (Commission Internationale de l'Eclairage coordinates ranging from (x, y) = (0.45, 0.40) to (0.35, 0.39) at 2.9-3.3 V with high color rendering indices up to 80. Peak external quantum efficiency and peak power efficiency of the white LEC reach 4% and 7.8 lm/W, respectively. These results suggest that white LECs based on host-guest cationic transition metal complexes may be a promising alternative for solid-state lighting technologies.  相似文献   

18.
The complex [Ir(ppy)(2)(pphen)][PF(6)] (Hppy = 2-phenylpyridine, pphen = 2-phenyl-1,10-phenanthroline) has been prepared and evaluated as an electroluminescent component for light-emitting electrochemical cells (LECs). Like in analogous LECs using bpy-based iridium(III) complexes a significant enhancement of the device stability is observed.  相似文献   

19.
We investigated the binding of sodium dodecyl sulfate (SDS) to various linear and star polymers of the nonionic methoxyhexa(ethylene glycol) methacrylate (PMHEGMA) and the ionic 2-(dimethylamino)ethyl methacrylate (PDMAEMA), the latter being a polycation at low pH. The dodecyl sulfate ion selective electrode (EMF), isothermal titration calorimetry (ITC), and surface tension (ST) were applied to gain detailed information about interactions. In all cases there is evidence of significant binding of SDS over an extensive SDS concentration range spanning from ca. 10(-6) to 0.1 mol dm(-3). At pH 3, the polymer PDMAEMA is a strong polycation and here the binding is dominated by electrostatic 1:1 charge neutralization with the anionic surfactant. At their natural pH of 8.6, PMHEGMA and PDMAEMA polymers are essentially nonionic and bind SDS in the form of polymer-bound aggregates in the concentration range of ca. 1 x 10(-3) to 3 x 10(-2) mol dm(-3). All the polymers also bind SDS to a lesser extent at concentrations below 1 x 10(-3) mol dm(-3) reaching as low as 10(-7) mol dm(-3). This low concentration binding process involves the polymer and nonassociated SDS monomers. As far as we are aware, this is the first example that such a low concentration noncooperative binding process could be observed in SDS/neutral polymer systems by EMF and ST. We also showed that the nonionic surfactant hexa(ethylene glycol) mono-n-dodecyl ether (C12EO6) and the cationic cetyltrimethylammonium bromide (C16TAB) interact with star PDMAEMA. We believe that the interaction of C12EO6 and CTAB is of similar noncooperative type as the first SDS binding process in the range from ca. 10(-5) to 0.3 x 10(-3) mol dm(-3). At the high concentration binding limit Csat of SDS, the above polymers become fully saturated with bound SDS micelles. We applied small angle neutron scattering (SANS) to determine the structure and aggregation numbers of the star polymer/bound SDS micelles and calculated the stoichiometry of such supramolecular complexes. The SANS data on PDMAEMA star polymers in the presence of C12EO6 showed only a limited monomer binding in contrast to linear PDMAEMA, which showed monomer C12EO6 binding at low concentrations but micellar aggregates at 6 x 10(-3) mol dm(-3).  相似文献   

20.
We explore the possibility of producing polymer nanocomposites with an ordered distribution of nanoparticles by using an electropolymerizable liquid crystal (LC) monomer. The nanoparticles are added to the monomer before polymerizing it. We study the polymer derived from the LC (E)-6-(3-hydroxy-4-(((4-octyloxy)phenyl)imino)methyl)phenoxy)hexyl methacrylate (M6R8) both pure and in the presence of 3.4 nm TiO2 nanoparticles, at 30 wt%. This particular system is chosen since (1) the LC polymers we work with have the added advantage of having a specific orientation and structure which allows us to study its effect in the nanoparticles and (2) when considering the nanocomposite, it is polymerized with the nanoparticles included. The system is studied using grazing incidence small angle X-ray scattering and in-plane direction X-ray scattering. The polymer obtained alone appears to be tilted with respect to the surface of the substrate. The structure adopted by the nanoparticles in the nanocomposite is layered and apparently incommensurate with the polymer. It is formed through the association of the nanoparticles with the M6R8 aromatic cores during the process of electropolymerisation. This interpretation of the data is supported by the nanoparticle structures formed when the related, non-polymerizable LC, (E)-6-(3-hydroxy-4-(((4-octyloxy)phenyl)imino)methyl)phenoxy)hexyl isobutyrate (I6R8), is analysed. We find that for both, the pure polymer poly-((E)-6-(3-hydroxy-4-(((4-octyloxy)phenyl)imino)methyl)phenoxy)hexyl) methacrylate (EPM6R8) as well as the polymer with nanoparticles (EPM6R830TO), the electropolymerisation imposes a preferred growth direction of the polymer side chains, and therefore for the nanoparticle arrangement in the polymer.  相似文献   

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