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11.
We have investigated the molecular orientation of glassy poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) layers formed on photo-aligned polyimide films with different in-plane anisotropy. The polyimide contains azobenzene in the backbone structure (Azo-PI), allowing us to control the in-plane anisotropy of the film by varying linearly polarized light (LP-L) exposure. The glassy PFO layers (30 nm thick) were obtained by annealing the samples at the liquid crystalline phase of PFO and then quenching them to room temperature. The degree of alignment of PFO was assessed by the polarization ratio of photoluminescence (PL). The PL polarization ratio increased rapidly with the LP-L exposure, and it reached 10 at 2.8 J/cm2. Beyond this LP-L exposure, it became almost constant around 10.4. This PL polarization ratio was much higher than the absorption dichroic ratio of the underlying Azo-PI film. This result suggests that the degree of alignment of PFO is determined by its liquid crystalline nature. The saturation dependence of the degree of alignment is very useful for fabricating alignment patterns by a simple photo-mask exposure method. We have succeeded in fabricating 3 μm line-and-space alignment patterns of PFO. 相似文献
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The syntheses of new fluorene‐based π‐conjugated copolymers; namely, poly((5,5″‐(3′,4′‐dihexyl‐2,2′;5′,2″‐terthiophene 1′,1′‐dioxide))‐alt‐2,7‐(9,9‐dihexylfluorene)) (PFTORT), poly((5,5″″‐(3″,4″‐dihexyl‐2,2′:5′,2′:5″,2‴:5‴,2″″‐quinquethiophene 1″,1″‐dioxide))‐alt‐2,7‐(9,9‐dihexylfluorene)) (PFTTORTT), and poly((5,5‐E‐α‐(2‐thienyl)methylene)‐2‐thiopheneacetonitrile)‐alt‐2,7‐(9,9‐dihexylfluorene)) (PFTCNVT), are reported. In the solid state, PFTORT and PFTCNVT present red–orange emission (with a maximum at 610 nm) while PFTTORTT shows a red emission with a maximum at 666 nm. In all cases, electrochemical measurements have revealed p‐ and n‐dopable copolymers. All these copolymers have been successfully tested in simple light‐emitting diodes and show promising results for orange‐ and red‐light‐emitting devices. 相似文献
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X. Wang E. Perzon F. Oswald F. Langa S. Admassie M.R. Andersson O. Ingans 《Advanced functional materials》2005,15(10):1665-1670
Plastic solar cells have been fabricated using a low‐bandgap alternating copolymer of fluorene and a donor–acceptor–donor moiety (APFO‐Green1), blended with 3′‐(3,5‐bis‐trifluoromethylphenyl)‐1′‐(4‐nitrophenyl)pyrazolino[70]fullerene (BTPF70) as electron acceptor. The polymer shows optical absorption in two wavelength ranges, λ < 500 nm and 600 < λ < 1000 nm. The BTPF70 absorbs light at λ < 700 nm. A broad photocurrent spectral response in the wavelength range 300 < λ < 1000 nm is obtained in solar cells. A photocurrent density of 3.4 mA cm–2, open‐circuit voltage of 0.58 V, and power‐conversion efficiency of 0.7 % are achieved under illumination of AM1.5 (1000 W m–2) from a solar simulator. Synthesis of BTPF70 is presented. Photoluminescence quenching and electrochemical studies are used to discuss photoinduced charge transfer. 相似文献
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G. Heliotis R. Xia G.A. Turnbull P. Andrew W.L. Barnes I.D.W. Samuel D.D.C. Bradley 《Advanced functional materials》2004,14(1):91-97
We report the fabrication of optically pumped solid‐state polymer lasers based on the semiconducting polymer poly(9,9‐dioctylfluorene) (PFO) using resonator structures that offer one‐ and two‐dimensional distributed feedback. The lasers are readily fabricated by solution deposition of thin polymer films on top of suitable grating microstructures etched into fused silica substrates. The devices operate in the blue spectral region, are highly efficient (slope efficiencies as high as 7.8 % are demonstrated), and exhibit very low threshold energies for oscillation (0.8 nJ per pulse). The operating characteristics of the lasers are investigated in detail. The transverse mode profiles and divergence of the output beams are measured and correlated with the internal lasing modes and the feedback mechanism present in the resonators. Additionally, broadband tuning of the emission wavelength over a range of ~ 40 nm is demonstrated by controlling the supported resonant frequency of the laser cavities. 相似文献
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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. 相似文献
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聚芴衍生物是最有发展潜力的电致发光材料之一。本文从聚芴衍生物的结构出发,概述了通过化学方法对聚合物的性能进行优化的最新研究进展,着重于发光效率和发光稳定性、发光颜色、加工性能的改善方法。 相似文献
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S. H. Park Y. Jin J. Y. Kim S. H. Kim J. Kim H. Suh K. Lee 《Advanced functional materials》2007,17(16):3063-3068
Despite the promising expectations of poly(fluorene) (PF)‐type materials as efficient blue‐light‐emitting polymers, the devices based on these materials are not yet fully utilized. Under prolonged operation of the devices, the PF‐type materials undergo degradation with the appearance of a long‐range emission around 2.2–2.3 eV. As a consequence, the emissive color changes from blue to green with a decrease in the device efficiency. Here, an innovative approach that leads to a new blue‐emitting polymer with remarkable color stability is reported. By modifying the chemical structure of PF to inhibit the formation of keto defects, it is demonstrated that the devices exhibit excellent color stability. This new blue‐emitting polymer, poly(2,6‐(4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta‐[def]phenanthrene)) (PCPP), emits a stabilized, efficient blue electroluminescence without exhibiting any peak in the long‐wavelength region even after prolonged operation of the devices in air. 相似文献
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X. Gong P.K. Iyer D. Moses G.C. Bazan A.J. Heeger S.S. Xiao 《Advanced functional materials》2003,13(4):325-330
Polyfluorene (PF)‐based light‐emitting diodes (LEDs) typically exhibit device degradation under operation with the emergence of a strong low‐energy emission band (at ~ 2.2–2.4 eV). This longer wavelength band converts the desired blue emission to blue–green or even yellow. We have studied both the photoluminescence (PL) and electroluminescence (EL) of PFs with different molecular structures and found that the low‐energy emission band originates from fluorenone defects which are introduced by photo‐oxidization, thermal oxidation, or during device fabrication. X‐ray photo‐emission spectroscopy (XPS) results show that the oxidation of PF is strongly catalyzed by the presence of calcium. The fluorenone defects generate a stronger contribution to the EL than to the PL. By utilization of a novel electron‐transporting material as a buffer layer between the emissive PF and the Ca/Ag (Ba/Ag) cathode, the blue EL emission from the PF was stabilized. 相似文献