HIGH-FREQUENCY ALTERNATING-CURRENT LIGHT-EMITTING-DIODES USING LANGMUIR-BLODGETT-FILMS

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. All rights reserved.