title: Deep blue exciplex organic light-emitting diodes with enhanced efficiency; P-type or E-type triplet conversion to singlet excitons?
abstract: Simple trilayer, deep blue, fluorescent exciplex organic light-emitting diodes (OLEDs) are reported. These OLEDs emit from an exciplex state formed between the highest occupied molecular orbital (HOMO) of N,N'-bis(1-naphthyl)N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) and lowest unoccupied molecular orbital (LUMO) of 1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBi) and the NPB singlet manifold, yielding 2.7% external quantum efficiency at 450 nm. It is shown that the majority of the delayed emission in electroluminescence arises from P-type triplet fusion at NPB sites not E-type reverse intersystem crossing because of the presence of the NPB triplet state acting as a deep trap.
authors.affiliation: Physics Department, University of Durham, Durham, UK. vygintas.jankus@durham.ac.uk
authors.forename: Vygintas
authors.initials: V
authors.lastname: Jankus
authors.forename: Chien-Jung
authors.initials: CJ
authors.lastname: Chiang
authors.forename: Fernando
authors.initials: F
authors.lastname: Dias
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Monkman