Alternating current (AC) light emitting diodes (LEDs) have been fabric
ated where Langmuir-Blodgett (LB) films of quinquethiophene (QT) or po
ly(3-hexylthiophene) (PHT) have been used as the active material sandw
iched between insulating LB layers of poly(methylmethacrylate) (PMMA)
or emeraldine base polyaniline (PANI), respectively. The frequency res
ponse of the devices has been studied, and as the frequency limit of o
peration we have used the -3 dB frequency. We have shown that high fre
quency AC LEDs can be fabricated with as few as 10-15 LB layers of the
active material. Electroluminescence (EL) is observed almost equal in
intensity in both biases for PMMA/QT/PMMA devices. The EL spectrum fo
r these devices shows a broadening to the low-energy side as compared
with the photoluminescence (PL) spectrum. The role of the interfaces f
or the frequency response is discussed. (C) 1998 Elsevier Science S.A.
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