Simultaneous exciton control and electron recycling in pyrene-based stable blue fluorescent organic light-emitting diodes via hybridized local and charge transfer and triplet-triplet fusion mechanisms

초록

While anthracene-based fluorescent materials utilizing triplet–triplet fusion (TTF) can theoretically achieve internal quantum efficiencies (IQEs) up to 62.5 %, their performance is hindered by non-emissive high-lying triplet state (Tn, n ≥ 2) excitons and instability caused by electron leakage. To address this, we report a pyrene-based fluorescent emitter, 9-(4-(6-(4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)pyren-1-yl)phenyl)-9H-carbazole (p-CPI), which simultaneously exhibits TTF and hybridized local and charge transfer (HLCT) characteristics. Transient electroluminescence (TrEL) and magneto-electroluminescence (MEL) measurements confirm that the HLCT pathway facilitates high-lying reverse intersystem crossing (hRISC), allowing non-radiative triplet excitons to contribute to emission, thereby suppressing triplet-related quenching and enhancing device stability. As a result, a non-doped p-CPI device achieves an LT70 (the time taken for the luminance to decrease to 70 % of its initial value) of 115 h, corresponding to more than a 50-fold improvement in operational lifetime compared to a conventional TTF-based device. Furthermore, when used as an electron harnessing and recycling (EHR) layer between the emissive layer (EML) and electron blocking layer (EBL), p-CPI captures and recycles leakage electrons while protecting the EBL from degradation, resulting in a slightly improved external quantum efficiency (EQE) of 7.49 % and extending the operational lifetime to an LT70 of 27 h, more than a twofold enhancement compared to the reference device. This dual-channel exciton management and EHR strategy offers a promising approach for overcoming the long-standing efficiency-lifetime trade-off in blue fluorescent organic light-emitting diodes (OLEDs). © 2025 Elsevier B.V.

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