Quantum efficiency improvement in anthracene-based organic light-emitting diodes codoped with a hole-trapping material

摘要

We focus on organic light-emitting diodes having an N,N'-di(l-naphthyl)-N,N-diphenylbenzidine (NPB) hole-transport layer, a doped light-emitting layer (LEL) based on a 9,10-diarylanthracene (DAA), and a tris(8-quinolinolato)aluminum (Alq) electron-transport layer. The addition of a hole-trapping codopant, e.g., NPB, to the LEL can triple the external quantum efficiency (EQE), which can reach 3%-6%. We discuss (a) the magnitude of the effect and the causes,rn(b) the effect on the drive voltage, emission spectrum, and operating lifetime, and (c) the approaches to higher EQEs of 5%-10%. We compare (a) various blue and green LEL dopants, (b) NPB codopant with aminated polycyclic aromatic hydrocarbons, which reduce the EQE, andrn(c) the DAA-based cells with their Alq-based counterparts.