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1 December 1997 Electroluminescence in poly(p-phenyleneethynylene)-based devices
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In recent years there has been a considerable interest int he photoluminescence (PL) and electroluminescence (EL) properties of conjugated polymers, because of their potential application as the emitting layer in light- emitting devices. While poly(p-phenylenevinylene) (PPV) and its derivatives have been investigated most intensively among Al conjugated polymers, only few studies have been made on poly(p-phenyleneethynylene)s (PPEs), which feature a triple rather than a double bond in the conjugated backbone. Here we present out recent experiments on polymer light- emitting diodes (LEDs) based on poly(2,5-dialkoxy-p- phenyleneethynylene)s. The devices under investigation consist of the PPE emitting layer which is sandwiched between an indium tin oxide (ITO) and an aluminium, calcium or chromium electrode. Yellow-green electroluminescence with a brightness of up to 20 cd/m2 was observed for different PPEs. The EL intensity follows the applied bias and current as expected, and the EL emission essentially matches the PL spectrum. Interestingly, no significant difference in device performance was observed with respect to internal quantum efficiencies and onset-voltage, when comparing Al and Ca electrodes. These results suggest, that in the case of PPEs the hole injection barrier seems to be a limiting factor, while the injection of electrons from the low work function electrode is facilitated. Consequently, these devices favorably comprise an electron injecting contact with moderate work function which, as expected, was also found to lead to an improved device stability.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Andrea T. Montali, Christoph Weder, and Paul Smith "Electroluminescence in poly(p-phenyleneethynylene)-based devices", Proc. SPIE 3148, Organic Light-Emitting Materials and Devices, (1 December 1997);

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