White emission from a single-component single-layer solution processed OLED

We report white electroluminescence from a single component-single layer solution processed organic light emitting diodes (OLEDs). In this work, we have fabricated and characterized OLEDs based on a single polymer synthesized by incorporating a small amount of the orange-light emitting chromophore 1,8-Naphtalimide derivative as side chain to poly(fluorene-alt-phenylene) (PFP). The structure of the devices is ITO/PEDOT:PSS/Active layer/Al. The dopant unit was convalenttly attached to the side chain of polyfluorene by alkyl spacers. We have fabricated devices with different amounts of the orange chromophore (0, 0.0005, 0.005, 0.02 and 0.08 in weight) as well as a device based on a physical blend in the same proportion of 0.08 for comparison purposes. Absorption and Photoluminescence (PL) studies in thin films show no significant interaction can be observed between both moieties in the ground state, but after photoexcitation an efficient energy transfer takes place from PFP to the orange chromophore. We have observed a more efficient energy transfer in these compounds than for physical mixtures of the two chromophores due to a phase separation effect in the blend confirmed by the optical measurements and ESEM analysis, obtaining energy transfer even in diluted solutions from the intramolecular interaction in the copolymers. With this very simple device structure, white light with Commission Internationale de l'Eclairage (CIE) coordenates (0.34;0.43) is obtained for the electroluminescence (EL) emission and turn on voltage of 6 V for the device based on the copolymer with x = 0.02, together with a good match in the EL and PL spectra indicative that two emissions are produced by the same species, making this material very suitable for large area solution processed devices in solid state illumination.