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

作者：Bai, Rubing; Meng, Xianwen; Wang, Xiaoxiang; He, Lei^*

来源：Advanced Functional Materials, 2021, 31(3): 2007167.

DOI：10.1002/adfm.202007167

• blue
• exciplex
• host-guest
• light-emitting electrochemical cell
• thermally activated delayed fluorescence

The 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-ImMePF(6)), 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-ImEtPF(6)), are developed to form the ionic exciplex host. The mixed film of tbuCAZ-ImMePF(6)and TRZ-ImEtPF(6)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.