Abstract:
In this study, we propose a strategy to offset charge trapping and to enhance the confinement of excitons in
the emissive layer of white electroluminescent copolymer using a luminogen with aggregation-induced
emission enhancement (AIEE). The fluorenone-based luminogen, 2,7-bis(9H-fluoren-9-one-2yl)-9,9-
dihexylfluorene (FF) that exhibited yellow emission with AIEE property is copolymerized with 9,9-
dihexylfluorene in different compositions to tune the emission color. White-light emission is
demonstrated in a copolymer FF-0.25, which contained 0.25% of FF in the polymer backbone.
Interestingly, the copolymers exhibited enhanced emission upon aggregation in thin film, even in low FF
composition. OLEDs fabricated from the copolymer FF-0.25 elicited a white electroluminescence with
Commission Internationale de l'Eclairage (CIE) coordinates of 0.30, 0.31 with a power efficiency of 4.12
lm W 1. FF-0.25 showed very low charge trapping compared to other white emitting single polymer
OLEDs reported to date. The reduced charge carrier trapping is attributed to the positioning of energy
levels in the copolymer that resulted in almost equal electron- and hole-injection barriers. A theoretical
investigation on the copolymers of FF revealed the presence of an ambipolar property and low exciton
binding energy implicit of efficient formation and confinement of excitons within the emissive layer. The
system represents the first ambipolar white electroluminescent polymer designed by using an AIEE
luminogen
