Light-emitting diodes from dye-insulating matrix Langmuir-Blodgett films

Abstract

Light-emitting diodes (LEDs) utilizing a dye-insulating matrix blend have been fabricated with the Langmuir-Blodgett technique. The emitting dye material used was Rubrene, while poly(methylmethacrylate) (PMMA) was used as the insulating matrix material. The luminance-current density characteristics were studied as a function of Rubrene/PMMA molar ratio which ranged from 5:95 to 60:40 mol.% of Rubrene/PMMA. Devices with low concentrations of Rubrene were found to emit approximately the same amount of light as devices containing higher concentrations of the emitting material. The thickness dependence of luminance vs. applied voltage was studied for devices with 'optimal' molar ratio between Rubrene and PMMA. The thickness of the LEDs studied ranged from three to 11 molecular layers. Photoluminescence and electroluminescence spectra of the LEDs were compared. The quantum efficiency for the LED configuration was calculated.