Study of organic light-emitting diodes with exciplex and non-exciplex forming interfaces consisting of an ultrathin rubrene layer

• OLEDs with exciplex interface consisting of an ultrathin rubrene were fabricated.
• Energy transfer and triplet up-conversion were responsible for exciplex device.
• Direct charge trapping was dominated in non-exciplex-type device.

Fluorescent organic light-emitting diodes (OLEDs) with exciplex and non-exciplex forming interfaces, where an ultrathin 5,6,11,12,-tetraphenylnaphtacene (rubrene) emissive layer was sandwiched, were fabricated. The performances of 4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA)/1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) exciplex-type device and 4,4′-di(9H-carbazol-9-yl)biphenyl (CBP)/TPBi no-exciplex-type device were optimized in terms of the thickness of rubrene ultrathin layer. The results showed that the exciplex-type device yielded high device efficiency, attributing to the utilization of triplet excitons as the triplets of the exciplex can be up-converted into singlets via reverse intersystem crossing. The light emission process in exciplex-type device was dominated by energy transfer, while the non-exciplex type device was dominated by charge trapping emission mechanism, which was verified by the single carrier devices.

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