Performance of organic light-emitting diodes with a mixed emitting layer: Relationship between mixed-layer carrier mobility and efficiency/lifetime

摘要

Charge transport behaviors in mixed thin films of NPB (N,N'-diphenyl-N,N'-bis(1-napthyl)-1,1 '-biphenyl-4,4'-dia mine) and Alq_3 (tris(8-hydroxyquinoline) aluminum) were investigated by using a time-of-flight (TOF) technique. The dependence of the extracted charge mobilities on the compositional fraction was interpret by the HOMO and LUMO energy levels and the charge mobilities of the neat compounds, and the nature of microscopic networks within the mixed systems. The carrier conduction characteristics were used to illustrate the electrical and optical properties of the organic light emitting devices (OLEDs) with a mixed layer. In addition, the dependence of the device lifetime performance on the compositional fraction is consistent with the degradation model based on cationic Alq_3 species. This study reveals the fundamental nature of charge transport in the mixed organic semiconductors and shed a new light on designing high performance OLEDs.