Langmuir-Blodgett films of conjugated polymers: electroluminescence and charge transport mechanisms

This paper reviews and reports our work on the development of polymeric light-emitting diodes (LEDs) based on Langmuir-Blodgett (LB) films. We have used LB deposition technique as a tool to fabricate dc and ac LEDs with a precise thickness ranging from a few molecular layers to tens of layers. In de LEDs, we have shown that as few as three LB layers of active polymer can yield the same luminance as the thicker ones. With the advantage of LB deposition technique to fabricate heterostructure (multilayer) devices, we have used carrier transporting materials and carrier blocking LB films to control and balance the charge injections in dc LEDs. The frequency dependence of (multilayered) ac LEDs has been studied and moderately high-frequency (20 kHz) electroluminescence (EL) intensity has been obtained. From the transient EL measurements, the role of interfaces in polymeric LEDs has been emphasized and the operation mechanism of LED's has been discussed.