A mechanistic study of exciplex formation and efficient red light-emitting devices based on rare earth complexes

Abstract

Abstract The mechanisms of exciplex formation between hole-transporting material N,N ′ -diphenyl- N,N ′ -bis(3-methylphenyl)-1,1 ′ -diphenyl-4,4 ′ -diamine (TPD) and electron-transporting materials tris(dibenzoylmethanato)-mono(bathophenanthroline)-rare earth (RE(DBM) 3 bath) in TPD/RE(DBM) 3 bath bilayer electroluminescence (EL) devices were studied. The formation process was identified by using fluorescent dye as dopant. It was found that interaction between the excited states of RE(DBM) 3 bath and the ground state of TPD molecules resulted in the exciplex. The recombination zone of the TPD/RE(DBM) 3 bath device was proved to be mainly in the RE(DBM) 3 bath layer near the organic interface. On the other hand, by using dopant as efficient energy acceptor in RE-complex hosts, we found that exciplex emission was quenched thoroughly and efficient red light emission was observed, proving that RE(DBM) 3 bath may act as an efficient energy donor in EL devices. In the case of Eu 3+ as the central ion, maximum EL efficiency and highest brightness of red light emission reached 2.6% and 2000 cd/m 2 , respectively.