An attractive approach to full color OLED displays is based on white emitting copolymers and color filters. In this paper the special impact of broadband emitting copolymers based on polyspirobifluorene structures is discussed. The EL spectra of broadband emitters in PLEDs are strongly influenced by interference effects as well as by the driving conditions. Experimental results could be confirmed by modelling. Adjustment of emission spectra to the color filter characteristics lead to improved efficiency.
Flexibility is one of the most frequently mentioned advantages if organic light emitting diodes are compared to other display technologies. In this contribution we show how the different functional layers respond to applied mechanical stress. To characterize the intrinsic flexibility of the stacked layers in an organic light emitting diode separately, samples with anode and cathode layers on flexible plastic substrates are investigated separately first. We observe that the ITO can withstand more than 30 000 bending cycles, concave as well as convex, down to a radius of curvature of 8 mm without apparent damage. Furthermore, the operational characteristics of completed flexible organic light-emitting devices built on indium-tin oxide coated poly(ether sulfone) under single bending cycles are investigated. Performance data taken at 15 mm radius of curvature show no influence compared to the non-planar conditions.
We describe a novel method to measure permeation rates for oxidizing agents with very high sensitivity. The technique is based on monitoring the resistance of a degrading Ca sensor in situ, inside a climate chamber. A sensitivity limit below 10-6 g/m2 day is reported for accelerated measurement conditions of 38°C and 90% relative humidity. The benefits of the method are demonstrated for single- and double-sided barrier foils, and the temperature and humidity dependence of the transport through PET is analyzed in detail. The method is also applied to obtain permeation rates for a barrier-coated substrate after as well as during bending. Theoretical simulations are used to evaluate the influence of a defect-dominated transport mechanism on the experimental results and to model the time evolution of the concentration profile in a double-barrier stack. Implications for the development of barrier-enhanced substrates for flexible OLED applications are discussed.