Investigation of energy transfer and charge trapping in dye-doped organic light-emitting diodes by magneto-electroluminescence measurement

We investigated the energy transfer and charge trapping (CT) in dye-doped organic light-emitting devices by using the magneto-electroluminescence as a tool. An intra-molecular charge-transfer fluorescent material N,N-diphenyl-4-(9-phenylnaphtho-[2,3-c][1,2,5]thiadiazol-4-yl)aniline was selected as the guest emitter. The tri-(8-hydroxyquinoline)-aluminum and 1,3-bis(9-carbazolyl)benzene were selected as the hosts. Our results demonstrate that as the energy difference between the HOMO (highest occupied molecular orbital)/LUMO (lowest unoccupied molecular orbital) of the host and the guest (ΔE_HOMO/ΔE_LUMO) increases, the CT becomes more dominant, and the CT cannot be ignored even when the ΔE _HOMO/ΔE_LUMO is small and the emission spectrum of the host overlaps the absorption spectrum of the guest well.