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초록

We investigated the impact of the structural, electrical, and electronic properties of multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters on the variation in device performance as a function of the concentration of the phosphorescent sensitizer and the relative energy levels. Devices employing tDPA-DtCzB exhibited significantly reduced variations in external quantum efficiency (EQE) and operational lifetime compared to those utilizing tDMAC-DtCzB. This improved stability primarily arose from the precise spectral alignment between the main emission peak of the sensitizer and the narrow absorption peak of tDPA-DtCzB, which facilitated efficient Förster resonance energy transfer (FRET) even at low sensitizer concentrations. Furthermore, quantitative analyses of trap-related parameters, such as trap activation energy (Ea) and demarcation energy level (Eω), demonstrated that maintaining consistent hole trapping sites localized on the sensitizer effectively minimized performance variation. Thus, we highlight that optimal spectral alignment and controlled hole trapping characteristics are essential for realizing sensitizer concentration-insensitive and high-performance phosphor-sensitized TADF organic light-emitting diodes (PST OLEDs). © 2025 Elsevier B.V.

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