Conjugated polymer MEH-PPV

Li Q, Hua R, Chou KC (2008) Electronic and conformational properties of the conjugated polymer MEH-PPV at a buried film/solid interface investigated by two-dimensional IR-visible sum frequency generation. J Phys Chem B 112 2315-2318... 

FIGURE 10.18 The band diagram at zero bias (right), flat-band conditions (middle), and at forward bias (right) illustrated schematically according to the MIM picture for the conjugated polymer MEH-PPV. 

Fig. 5 (a), (c) Fluorescence intensity transients of a single conjugated polymer (MEH-PPV) spun from toluene and chloroform solution, respectively, (b), (d) Time-evolution of spectra of a MEH-PPV molecule spun from toluene and chloroform, respectively. Spectra are offset in vertical direction and labeled with the time at which they were taken. Reprinted with permission of [20], copyright (2001) Elsevier... 

Figure 1. Example for single molecule behavior Intensity transient of a single molecule of the conjugated polymer MEH-PPV (Poly[2-methoxy,5-(2 -ethyl-hexyloxy)-jC>-phenylene-vinylene]) (see insert for structure). The transient exhibits intermittent photoluminescence from several discrete intensity levels until the molecule imdergoes final photobleaching after approximately 215 s.

Figure 11.15 Schematic diagram of a Ca/MEH-PPV/ITO photodiode which is reversely biased (ITO as cathode and Ca as anode) compared with an LED. An electron-hole pair is formed in the conjugated polymer MEH-PPV upon absorption of a photon. The tvw) charge carriers separate and migrate to the attracting electrode, thus contributing to the photocurrent.

Figure 3.21 shows the transient spectra observed following pulse radiolysis of an argon-saturated solution of biphenyl (10 mM) and the conjugated polymer MEH-PPV in benzene solution. 

The rest of this chapter will focus primarily on results using the soluble PPV-based polymer MEH-PPV. The results obtained for MEH-PPV are typical of the conjugated polymers used in LEDs. The models and results presented are generally applicable. They describe the operation of a wide range of polymer LEDs if the appropriate polymer film properties arc used. 

Figure 15-29. Chemical structures of the conjugated polymers used in the device and the device structure of the laminated solar cell. For the top half of the device, A1 or Ca was evaporated on glass substrates, and the acceptor material MEH-CN-PPV (and a small amount of POPT, usually 5%) was spin coaled. The half with the POPT (and a small amount of MEH-CN-PPV, usually 5%) was spin coaled on 1TO substrates and heated to 200"C under vacuum belore the device was laminated together by applying a light pressure.

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. 

The first realization of a conjugated polymer/fullerene diode [89] was achieved only recently after the detection of the ultrafasl phoioinduced electron transfer for an lTO/MEH-PPV/CW)/Au system. The device is shown in Figure 15-18. Figure 15-19 shows the current-voltage characteristics of such a bilayer in the dark at room temperature. The devices discussed in the following section typically had a thickness of 100 nm for the MEH-PPV as well as the fullerene layer. Positive bias is defined as positive voltage applied to the 1TO contact. The exponential current tum-on at 0.5 V in forward bias is clearly observable. The rectification ratio at 2 V is approximately l()4. 

Although MEH-PPV 13 (at the time of discovery) was one of the most efficient soluble polymers for PLEDs application, its performance is not high enough for commercialization as LEP. One of the reasons is unbalanced hole-electron mobility in MEH-PPV (the mobility of holes is 100 times faster than the mobility of electrons) [133]. Copolymerization with other conjugated monomers, to some extent, can improve the electron-transporting properties and increase the EL performance. 

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. ... 

Nguyen TQ, Martini IB, Liu J, Schwartz BJ (2000) Controlling interchain interactions in conjugated polymers the effects of chain morphology on exciton-exciton annihilation and aggregation in MEH-PPV films. J Phys Chem B 104 237... 

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