Self-organized gradient hole injection to improve the performance of polymer electroluminescent devices

A new approach to forming a gradient hole-injection layer in polymer light-emitting diodes (PLEDs) is demonstrated. Single spin-coating of hole-injecting conducting polymer compositions with a perfluorinated ionomer results in a work function gradient through the layer formed by self-organization, which leads to remarkably efficient single-layer PLEDs (ca. 21 cd A(-1)). The device lifetime is significantly improved (ca. 50 times) compared with the conventional hole-injection layer, poly(3,4-ethylene-dioxythiophene)/poly(styrene sulfonate). These results are a good example for demonstrating that the shorter lifetime of PLEDs compared with small-molecule-based organic LEDs (SM-OLEDs) is not mainly due to the inherent degradation of the polymeric emitter itself. Hence, the results open the way to further improvements of PLEDs for real applications to large-area, high-resolution, and full-color flexible displays.