White emission from exciplex-based polymer light-emitting electrochemical cells

Light-emitting electrochemical cells (LECs) are seen as a promising technology that could usher in a new generation of lighting devices that are both energy- and cost-efficient. This has created an urgent need for highly efficient white-emitting LECs. Technologies have to be developed for realizing efficient white emission, suited to the simple structure of LEC devices. Utilizing exciplex emission is one means of obtaining white emission. In this chapter, the authors present an approach to obtaining white emission based on emission from exciplexes formed between a fluorescent conducting polymer (FCP) and aromatic amines. The exciplexes, which are complexes that can form between molecules in the excited state, emit light as electrons are transferred from the lowest unoccupied molecular orbital (LUMO) of the FCP to the highest occupied molecular orbital (HOMO) of the amine. The exciplex emission includes longer wavelengths and is broader in spectrum than the excitonic emission of FCP, such that white light can be obtained by combining the two types of emissions. By using the right amine in the proper concentration, we were able to produce white emission with x/y CIE color coordinates of 0.33/0.31 and a color rendering index (CRI) of 80 with a device having only a single active layer.