A design strategy for blue MR-TADF emitter with long lifetime and high color purity: Deactivated hole trapping and Dexter energy transfer pathway by highly twisted substitution

초록

Due to planar it-frameworks, multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters commonly suffer from severe concentration quenching and energy-loss via Dexter energy transfer (DET), which critically limit device efficiency and operational stability. To address these challenges, we designed a new pure-blue MR-TADF emitter, TPh-BDBF, by incorporating both dibenzofuran (DBF) and ortho-terphenyl amine units. The newly designed TPh-BDBF emitter demonstrated an enhanced reverse intersystem crossing (RISC) rate arising from an extended it-framework containing DBF moieties. Notably, the ortho-terphenyl amine units effectively suppress concentration quenching and DET while simultaneously acting largely as electrically inert moieties that prevent hole trapping. As a result, nonradiative energy loss through DET was significantly suppressed, leading to simultaneous improvements in device efficiency and operational stability. Devices based on TPh-BDBF exhibited a high external quantum efficiency (EQE) of 28.4% even at high doping concentrations. Furthermore, when employed as the terminal emitter in a phosphorescent-sensitized fluorescence (PSF) device, TPh-BDBF achieved CIE coordinate (0.13, 0.11) as well as LT80 of 53.1 h, which was a threefold enhancement compared with the emitter t-DABNA.

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