Mitigating Efficiency Roll-Off in Phosphor-Sensitized Fluorescence OLEDs via Molecular Polarity-Based Benzofuropyridine Host Engineering

초록

Two benzofuropyridine-based n-type host materials incorporating dibenzofuran core, 4,6-bis(benzofuro[2,3-b] pyridin-3-yl) dibenzo [b, d] furan (BFPDB-1) and 4,6-bis(benzofuro[2,3-b] pyridin-6-yl) dibenzo [b, d] furandibenzo [b, d] furan (BFPDB-2), were designed to investigate the impact of positional isomerism on exciton management in OLEDs. Subtle relocation of the pyridine nitrogen significantly modulates molecular polarity, charge-transfer character, and emissive-layer morphology, as confirmed by theoretical and experimental analyses. While conventional phosphorescent devices exhibit comparable efficiencies, pronounced performance differences emerge in phosphor-sensitized fluorescence (PSF) OLEDs. The BFPDB-2-based PSF device achieves a maximum external quantum efficiency of 22% and retains 20.7% EQE at 10,000 cd m-2 . This suppressed roll-off is consistent with improved energy funneling and reduced short-range local association, as suggested by transient photoluminescence (TRPL) and molecular dynamics (MD) / radial distribution function (RDF) analyses, which are associated with the distinct physicochemical properties of BFPDB-2, including its larger dipole moment, improved charge-transport balance, and more spatially distributed host-guest arrangement. These findings suggest that precise heteroatom placement, which enables modulation of molecular polarity, is a promising design direction for improving host-guest interactions and achieving high-efficiency, low-roll-off PSF OLEDs.

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