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3 March 2003 Poly(fluorene-co-benzothiadiazole)s: Effect of structure, molecular weight and polydispersity on their performance in polymer light-emitting diodes
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Copolymers based on fluorene and benzothiadiazole exhibit high brightness and quantum efficiencies when incorporated into polymer light-emitting diodes (PLEDs). Their emission wavelength is strongly dependent on the benzothiadiazole-containing segment of the polymer. However, the chain structure and charge-transport and -transfer processes in these materials are not well studied. We report the synthesis of a structural-random (r-PF3B) and a structural-defined (s-PF3B) copolymer, poly-fluorene-co-benzothiadiazole whereas the ratio of the two co- monomers was chosen to be 75% and 25%, respectively. We have systematically investigated the effect of structure on their photoluminescence (PL) and electroluminescence (EL) properties. Furthermore we have also studied the effect of molecular weight and its distribution on the performance of the material in PL and EL. We have found that the absorption and emission spectra (PL and EL) of these polymers are quite independent of their structures, molecular weights, and polydispersity. However, the PL and EL efficiencies do vary with the materials studied. These materials were fabricated into a series of double-layer devices. Their external quantum efficiencies (ranging from 0.097% to 1.7%) and maximum brightness (ranging from 153 to 23300 cd/m2) are highly dependent on the structure as well as the molecular weight and polydispersity. The higher the molecular weight and the narrower the distribution are, the higher the efficiency and brightness of the devices. Likewise, the structure of the polymer also influences the efficiency. It was found that the structural-random copolymer (r-PF3B) exhibits higher efficiencies and brightness when compared with the structural-defined one (s-PF3B) in the same molecular weight range.
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Petra Herguth, Xuezhong Jiang, Michelle S. Liu, and Alex K.Y. Jen "Poly(fluorene-co-benzothiadiazole)s: Effect of structure, molecular weight and polydispersity on their performance in polymer light-emitting diodes", Proc. SPIE 4800, Organic Light-Emitting Materials and Devices VI, (3 March 2003);

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