Color‐Stable, Efficient, and Bright Blue Light‐Emitting Electrochemical Cell Using Ionic Exciplex Host

Abstract

AbstractThe lack of high‐performance blue light‐emitting electrochemical cells (LECs) has remained a formidable challenge for fabricating white LECs for lighting applications. Here, a ionic exciplex host is used for color‐stable, efficient, and bright blue LECs by taking advantage of its facilitated carrier injection, bipolar charge‐transport, and efficient energy transfer to the guest dopant. A cationic donor molecule, 1‐(3‐(3,6‐di‐tert‐butyl‐9H‐carbazol‐9‐yl)phenyl)‐3‐methyl‐1H‐imidazol‐3‐ium hexafluorophosphate (tbuCAZ‐ImMePF6), and a cationic acceptor molecule, 1‐(3‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐3‐ethyl‐1H‐imidazol‐3‐ium hexafluorophosphate (TRZ‐ImEtPF6), are developed to form the ionic exciplex host. The mixed film of tbuCAZ‐ImMePF6 and TRZ‐ImEtPF6 affords blue exciplex with fast reverse intersystem crossing and thermally activated delayed fluorescence. For the film doped with a blue‐emitting iridium complex, energy is efficiently transferred from the exciplex to the complex. Host‐guest LECs using the doped film as the active layer show stable blue emission color and high current efficiencies of up to 25.8 cd A−1. More importantly, they attain simultaneously high efficiency and high brightness (14.1/17.4/16.8 cd A−1 at 705/872/1680 cd m−2), which are the most efficient and bright host‐guest blue LECs reported so far. The primary host‐guest LEC also exhibits promising operational stability. The work reveals that the use of an ionic exciplex host is a promising avenue toward high‐performance blue LECs.