Polymeric Light-Emitting Diodes Based on Poly(p-phenylene ethynylene), Poly(triphenyldiamine), and Spiroquinoxaline

In this paper polymeric light-emitting diodes (LEDs) based on alkoxy-substituted poly(p-phenylene ethynylene) EHO-OPPE as emitter material in combination with poly(triphenyldiamine) as hole transport material are demonstrated. Different device configurations such as single-layer devices, two-layer devices, and blend devices were investigated. Device improvement and optimization were obtained through careful design of the device structure and composition. Furthermore, the influence of an additional electron transporting and hole blocking layer (ETHBL), spiroquinoxaline (spiro-qux), on top of the optimized blend device was investigated using a combinatorial method, which allows the preparation of a number of devices characterized by different layer thicknesses in one deposition step. The maximum brightness of the investigated devices increased from 4 cd/m2 for a device of pure EHO-OPPE to 260 cd/m2 in a device with 25 % EHO-OPPE + 75 % poly(N,N′-diphenylbenzidine diphenylether) (poly-TPD) as the emitting/hole-transporting layer and an additional electron-transport/hole-blocking spiro-qux layer of 48 nm thickness.