Exciplex are generated at the heterojunction interface of electron donor and acceptor materials. Exciplex strategy can, thus, reduce molecular design difficulties for obtaining near-UV emission by selecting the appropriate electron donors and acceptors. Induced exciplex of Tris(4-carbazoyl-9-ylphenyl)amine (TCTA)/ 2,9-Dimethyl-4,7-diphenyl-1,10- phenanthroline (BCP) were applied to design deep blue organic light emitting diodes (OLEDs). BCP was used as an electron transport material and TCTA as a hole transporting material. The investigations carried out on planar-heterojunction have shown that recombination region was located at the vicinity of TCTA/BCP interface leading to exciplex formation. Furthermore, the thicknesses of BCP and TCTA layers play a key role in the control of the recombination zone and the emission color of the OLEDs. The electroluminescent spectra of planar-heterojunction exciplex-based OLEDs displayed deep blue emission at 423 nm with CIE coordinate of (0.16, 0.11). The emission of bulk-heterojunction exciplex-based OLEDs are also investigated showing that their emission is dominated by electroplex emission. The results demonstrate the feasibility of fabricating the efficient exciplex-based deep-blue OLED.
Numerous oxazole-based fluorophores show efficient emission in the UV and deep blue spectral range in the solid state, making them interesting candidates for use as emissive layers in organic light-emitting diodes (OLEDs). Three ozazole derivatives, i.e. 2-(p-tert-butylphenyl)benzoxazole (Bzx), 2-phenyl-naphthoxazole (Nzx) and 2,2’-di(p-tert-butylphenyl)- 6,6’-bibenzoxazole (BBzx), were used in OLEDs with neat films configurations. These molecules differ by their planarity, steric hindrance and size of the π-conjugated system. No photoluminescence was observed with Bzx and Nzx. In contrast, the incorporation of the bis-chromophore BBzx within thin solid films led to efficient emission. The corresponding OLEDs displayed a deep blue emission at 430 nm arising from the BBzx layer, with CIE coordinate of (0.157, 0.044). These specific optical features were attributed to the twisted molecular structure of the bis-chromophore, leading to reduction of the aggregation induced fluorescence quenching. An EQE of 1.2% was achieved with a driving current of 24 A/m2. The results suggest that BBzx derivatives may be useful as efficient color saturation deep-blue emitters in OLEDs.
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