Stable pure-blue phosphor-sensitized OLEDs utilizing a hypsochromic-shifting non-TADF fluorescent emitter

Abstract

A non-thermally activated delayed fluorescence (non-TADF) emitter is designed for stable and efficient pure-blue phosphor-sensitized fluorescent organic light-emitting diodes (PSF OLEDs). The designed emitter (DICz-2) has an indolocarbazole-based core characterized by a narrowband emission and substituents to tune the emission wavelength and promote Förster resonance energy transfer (FRET) from the phosphor by suitable expansion of the conjugation system as well as to prevent unfavorable Dexter energy transfer (DET) stemming from bulkiness. DICz-2 exhibits a narrowband photoluminescence (PL) of 14 nm full width at half maximum in the host film. In addition, the PL decay in the PSF system with DICz-2 is faster than that of a boron-containing TADF emitter, which demonstrates the effectiveness of non-TADF emitters in terms of quick deactivation of the high-energy excitons that cause degradation. PSF OLEDs using the DICz-2 emitter show hypsochromic-shifted emissions from the corresponding phosphorescent OLEDs due to the efficient FRET, and a tuned one achieves a set of principal OLED performances at a high degree: EQE = 18.7%, LT95 = 104.3 h, and Commission Internationale de L’Eclairage chromaticity coordinate (CIE)-y = 0.150 with an emission peak of 461 nm at 1000 cd m⁻².