White Organic Light-Emitting Diodes from Single Emissive Layers: Combining Exciplex Emission with Electromer Emission

Abstract

In this work, white light emission from the blend of a hole transport material, 4,4′-cyclohexylidene bis[N,N-bis(4-methylphenyl)benzenamine] (TAPC), and an electron transport material, 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1H-benzimidazole) (TPBi), was explored. Organic light-emitting diodes fabricated with the TAPC/TPBi blend as a single emissive layer showed sky blue exciplex emission at low voltages and yellow electromer emission at high voltages. Simultaneous emission of the blue exciplex and yellow electromer can be tuned to obtain pure white light emission. By combining the exciplex emission with field-induced electromer emission, pure white light emission with CIE color coordinates of (0.34, 0.31) was achieved. Transient electroluminescence measurements reveal the nature of the emission species. Electromer emission has significantly long-lived components as compared to the exciplex. The long electroluminescence decay obtained from electromer emission indicates possible utilization of triplet excitons in radiative recombination.