Recombination conjugated polymers

The enormous progress in the field of electroluminescent conjugated polymers has led to performances of oiganic light-emitting devices (LEDs) that are comparable and in some aspects superior to their inorganic counterparts 11). Quantum efficiencies in excess of 5% have been demonstrated [2] and show that a high fraction of the injected carriers in a polymeric electroluminescence (EL) device form electronic excitations which recombine radiatively. 

A. Haugencder, M. Ncgcs, C. Kallinger, W. Spirkl, U. Lemmer, J. Feldmann, U. Scherf, Non-linear emission and recombination in conjugated polymer waveguides. J. Appl. Pltys. 1999, 85. 1124. 

W Wohlgenannt, XM Jiang, C Yang, OJ Korovyanko, and ZV Vardeny, Spin-dependent polaron pair recombination in TT-conjugated polymers enhanced singlet exciton densities, Synth. Met., 139 921-924, 2003. 

Howard I A, Hodgkiss JM, Zhang XP, Kirov KR, Bronstein HA, Williams CK, Friend RH, Westenhoff S, Greenham NC (2010) Charge recombination and exciton annihilation reactions in conjugated polymer blends. J Am Chem Soc 132 328... 

Muller JG, Lupton JM, Feldmann J, Lemmer U, Scharber MC, Sariciftci NS, Brabec CJ, Scherf U (2005) Ultrafast dynamics of charge carrier photogeneration and geminate recombination in conjugated polymer fullerene solar cells. Phys Rev B 72 195208... 

The fill factor (FF), defined as Ima.xVma.x/IScVoc, is 0.25. The relatively low FF may be explained by recombination of charges at the ITO electrode. The present values of Isc and Voc are significantly enhanced in comparison with the device characteristics of a related Ceo-oligophenylenevinylene dyad [102] and quite similar to those previously reported for 7r-conjugated polymer/fullerene solar cells [115], although there has been considerable progress in energy conversion efficiencies of these devices recently [116]. 

The energy of the 7) state can also be determined for soluble conjugated polymers by the technique of T-T energy transfer (Monkman et al., 2001). When the solvent in a polymer solution is ionised with an intense, pulsed electron beam, charge recombination gives rise to excited solvent molecules in... 

Interest surged in studies of fluorescence after the discovery of electroluminescence from PPV (Burroughes et al., 1990), because of its potential for practical application in light emitting devices (LEDs). Electroluminescence is fluorescent emission produced by the recombination of electrons and holes injected into a thin film of conjugated polymer, and will be discussed in the next section. If photoluminescent emission from a polymer is weak, then the electroluminescence is unlikely to be of practical significance, and consequently studies of photoluminescence and photoluminescent quantum efficiency have been used as a means of selecting polymers likely to be useful in LEDs. 

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