Efficient polymer light-emitting diodes using conjugated polymer blends

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Abstract
Photoluminescence studies have been performed on poly [2,5-bis(cheolestranoxy)-1,4-phenylene vinylene] (BCHA) blends with poly(9,9-dioctylfluorene) (PF). The composition-independent, distinctive emission of BCHA in the BCHA/PF blends suggests the nonexistence of interchain species in the blends, due to polymer chain separation by bulky side groups. The electroluminescence(EL) efficiencies of devices made with BCHA/PF blends were also found to be superior to the BCHA-only devices. For example, the EL efficiency of the BCHA (10%)/PF device was 3.0 cd/A, which is about five times higher than a BCHA device. The basis for this enhancement has been attributed to improved charge injection and charge trapping in BCHA/PF blends. Holes are injected in these blends through the PF component and then transferred and trapped in BCHA, where radiative recombination subsequently occurs. As a result of improved minority-carrier injection, the turn-on voltages of the BCHA/PF devices are also much lower than the BCHA devices.