A study of organic light-emitting devices based on electrostatic self-assembled films of evans blue under AC voltage

Abstract

Light-emitting devices based on layer-by-layer electrostatic self-assembled films of evans blue have been fabricated. Poly (allylamine hydrochloride) with electrostatically attached evans blue molecules has been used as a polycation, while poly (acrylic acid) has been used as a polyanion. Luminance has been observed under both direct-current (dc) and alternating-current (ac) modes. Under dc voltage, luminance has been observed only in forward bias direction, while under ac voltage luminance has been observed under both, forward and reverse bias direction. Moderately high-frequency (50 kHz) electroluminescence (EL) has been obtained from these devices. Transient EL characteristics under a sequence of two voltage pulses have been studied. The light emissions under ac modes have been explained considering the recombination of injected holes (or electrons) with the leftover electrons (or holes) from the previous half-cycle. A correlation between the transient EL response and the frequency dependence of the ac EL has been established. The ac response of the EL has been simulated and compared with experimental results.