Light-emitting devices based on evans blue under alternating-current and direct-current modes: different charge injection mechanisms

Light-emitting devices (LEDs) have been fabricated with a blend of evans blue dye and poly(methylmethacrylate) (PMMA) insulating material. Luminance has been observed under both direct-current (DC) and alternating-current (AC) modes. Different charge injection and operation mechanisms have been shown to be applicable under DC and AC biases. From the current–voltage characteristics under DC voltage, Fowler–Nordheim (FN) tunnelling mechanism and Richardson–Schottky thermionic emission have been found to be applicable in forward and reverse bias directions, respectively. In general, luminance has been observed only in the forward bias direction. Under AC voltage, there has been accumulated hole-assisted electron injection, which has resulted in luminance in both bias directions for all molar concentrations of evans blue, and particularly higher luminance level in the reverse-biased half-cycle. Moderately high-frequency (40 kHz) electroluminescence (EL) has been obtained from these devices.