Poly 2 -methoxy- 5 -2 - ethylhexyloxy

The sulfonium precursor route may also be applied to alkoxy-substituted PPVs, but a dehydrohalogenation-condensation polymerization route, pioneered by Gilch, is favored 37]. The polymerization again proceeds via a quinomethide intermediate, but die syndicsis of the conjugated polymer requires only two steps and proceeds often in improved yields. The synthesis of the much-studied poly 2-methoxy-5-(2-ethylhexyloxy)-l,4-phenylene vinylene], MEH-PPV 15 is outlined in Scheme 1-5 33, 35]. The solubility of MEH-PPV is believed to be enhanced by the branched nature of its side-chain. 

Poly(2-methoxy, 5-(2 -ethylhexyloxy)-1,4-phenylene vinylene) MEH-PPV Emission peak = 605 nm p-type doping by sulfuric acid (H2SO4) -type doping by sodium (electron donor) Iodine (I2) = electron acceptor = > oxidizing agent... 

F. Wudl and G. Srdanov, Conducting Polymer Formed of Poly(2-Methoxy-5- (2 -Ethylhexyloxy)-p-Phenylene Vinylene), U.S. Patent 5,189,136, February 23, 1993. 

Examples of the optical pumping of solutions of luminescent conjugated polymers include laser action at 596 nm of poly[2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) using excitation with 6 ns Nd YAG third harmonic pulses (354.7 nm). ° Tuning of hexane solutions of the co-polymer poly(2,2, 5,5 -tetraoctyl-p-terphenyl-4,4 -xylene-vinylene-p-phenylenevinylene) (TOP-PPV) was possible between 414 and 456 mn, similar to the classical coumarin laser dyes. ... 

P. Kumar, A. Misra, M.N. Kamalasanan, S.C. Jain, R. Srivastava, V. Kumar, Charge transport through conducting organic poly(2-methoxy-5-(2-ethylhexyloxy)-l,4-phenylene vinylene),./. Phys. D Appl. Phys. 40 (2007) 561. 

These problems were eliminated by the use of modified PPV derivatives ", such as poly[2-methoxy-5-(2-ethylhexyloxy)-4-phenylene vinylene] (MEH-PPV) compound 2, see Table 6.1, which are soluble in organic solvents. The presence of lateral substituents in the polymers 3-6 shown in Table 6.1 induces a lower... 

The number of organic materials is of great interest in microelectronic and optoelectronic devices [1], In particular, the conjugated polymers, such as ladder-type methyl substituted poly-para-phenylene (Me-LPPP) and poly[2-methoxy-5-(2-ethylhexyloxy)-l,4-phenylene vinilene] (MEH-PPV) and their nanocomposites, have been widely investigated due to their perspectives in light-emitting diodes and solar cells [2—4]. 

The first realizations of polymer-polymer bulk heterojunction solar cells were independently reported in the mid-1990s by Yu and Heeger as well as by Halls et al. [28,30]. These solar cells were prepared from blends of two poly(para-phenylenevinylene) (PPV) derivatives the well-known MEH-PPV (poly[2-methoxy-5-(2 -ethylhexyloxy)-l,4-phenylenevinylene]) was used as donor component, while cyano-PPV (CN-PPV) served as acceptor component (identical to MEH-PPV with an additional cyano (- CN) substitution at the vinylene group). The blends showed increased photocurrent and power conversion efficiency (20-100 times) when compared to the respective single component solar cells. 

The second approach to PPV, is the Gilch synthesis [147], which consists in the introduction of solubilizing side groups, as represented in the case of the most studied dialkoxy derivative poly[2-methoxy-5-(2 -ethylhexyloxy)-l,4-phenylene vinylene] (MEH-PPV, XII) [29,148-150] (Fig. 9.20). 

Because the polymer cannot be processed as such due to its properties, a precursor polymer is synthesized, which is then processed, e.g., into hlms. In this form the hnal polymer is obtained by a post treatment. However, varieties of PPV with bulky substituents exhibit solubility in organic solvents. A commercial variety is poly(2-methoxy-5-(2 -ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV). 

Poly(2-methoxy-5-(3, 7 -dimethyloctyloxy)-l,4-phenylene vinylene), 117 Poly(2-methoxy-5-(2 -ethylhexyloxy)-l,4-phenylene vinylene), 31, 50, 91, 117 Poly(methyl-bis-(3-methoxyphenyl)-(4-propylphenyl)amine)siloxane, 42 Poly(methyl methacrylate), 32, 41, 100, 341, 499 Poly(2-methyl-5-vinyl)tetrazole, 319 Poly(l,5-naphthylene vinylene), 98 Poly(l,3,4-oxadiazole), 329 Poly(l,3,4-oxadiazole-2,5-diyl-l,2-vinylene), 337... 

Chart 1.8 Chemical structure of poly[2-methoxy-5-(2 -ethylhexyloxy)-p-phenylenevinylene], MEH-PPV. 

Fig. 1.25 Femtosecond spectroscopy. Differential transmission traces recorded at 2rec=S50 nm from thin films of poly[2-methoxy-5-(2 -ethylhexyloxy)-/ -phenylene vinylene], MEH-PPV, irradiated as indicated in the legend of Fig. 1.24 at varying photon...

Fullerene, Ceo, is quite an effective dopant. It is an excellent electron acceptor, capable of accepting up to six electrons. Photoinduced electron transfer from conducting polymers such as poly(3-octylthiophene), P30T, and poly[2-methoxy-5-(2 -ethylhexyloxy)-p-phenylene vinylene], MEH-PPV, to fullerene Ceo occurs on a timescale of less than 1 ps. A Ceo content of a few percent is sufficient to enhance 0CC in tbc ps time domain by more than an order of magnitude [56]. 

At the early development of polymer solar cells, a planar p-n junction structure represented the mainstream in mimicking conventional silicon-based solar cells. However, the obtained devices demonstrated poor photovoltaic performances due to the long distance between the exciton and junction interface and insufficient light absorption due to the thin light absorber. It was not until 1995 that the dilemma was overcome with the discovery of a novel bulk heterojunction in which donor and acceptor form interpenetrated phases. Poly[2-methoxy-5-(2 -ethylhexyloxy)-p-phenylene vinylene] was blended with Ceo or its derivatives to form the bulk heterojunction. A much improved power conversion efficiency of 2.9% was thus achieved under the illumination of 20 mW/cm. (Yu et al., 1995). The emergence of the donor/acceptor bulk-heterojunction structure had boosted the photovoltaic performances of polymer solar cells. Currently, a maximal power conversion efficiency of 10.6% had been reported on the basis of synthesizing appropriate polymer materials and designing a tandem structure (You et al., 2013). The detailed discussions are provided in Chapter 5. 

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