Dopant Emission Mechanism and the Effects of Host Materials on the Behavior of Doped Organic Light-Emitting Diodes

Organic light-emitting diodes made of tris-8-(hydroxyquinoline) aluminum as the electron-transport layers, N, N -diphenyl-N, N bis (3-methylphenyl)-1, 1 -biphenyl-4,4 -diamine (TPD) as the hole-transport layers, and 2-(1, 1-dimethylethyl)-6(2-(2, 3, 6, 7-tetrahydro-1, 1, 7, 7-tetramethyl-1H, 5H-benzo(ij) quinolizin-9-yl) ethenyl)-4H-pyran-4-ylidene) propanedinitrile (DCJTB) as the guest dopant have been studied. It is determined that a) emission from guest DCJTB in a host transport material results primarily from separate trapping of holes and electrons, rather than the more commonly proposed Förster transfer mechanism, b) DCJTB is a more efficient hole than electron trap, and c) the lifetime of a doped device is longer when TPD is used as the host material.