High frequency alternating current light-emitting diodes using Langmuir-Blodgett films

Abstract

Alternating current (AC) light emitting diodes (LEDs) have been fabricated where Langmuir-Blodgett (LB) films of quinquethiophene (QT) or poly(3-hexylthiophene) (PHT) have been used as the active material sandwiched between insulating LB layers of poly(methylmethacrylate) (PMMA) or emeraldine base polyaniline (PANI), respectively. The frequency response of the devices has been studied, and as the frequency limit of operation we have used the -3 dB frequency. We have shown that high frequency 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 for these devices shows a broadening to the low-energy side as compared with the photoluminescence (PL) spectrum. The role of the interfaces for the frequency response is discussed.