ScholarWorks@성균관대학교

초록

Deep-LUMO charge-generation layers (CGLs) have emerged as a robust alternative to doped CGLs for tandem organic light-emitting diodes (OLEDs), yet their performance remains fundamentally limited by large electron-injection barriers at the CGL interface. Here, we introduce an ultrathin strontium (Sr) interlayer as a charge-generation assistant layer (CAL) that simultaneously provides high optical transparency, smooth surface morphology, and effective modulation of interfacial energetics. Approximately 5-nm Sr films form continuous, highly transparent layers while generating interfacial dipoles and promoting trap-assisted tunneling (TAT) at the Bphen:Liq/HAT-CN interface. These combined effects reduce the effective electron-injection barrier from similar to 1.2 to similar to 0.3 eV. As a result, the tandem OLED exhibits ideal series turn-on behavior, balanced exciton recombination, and more than double the luminous efficiency of its single-unit counterpart, while maintaining comparable power efficiency. In addition, Sr integration narrows the electroluminescence spectrum through an enhanced microcavity effect, thereby improving color purity. Overall, this study identifies Sr as a new and highly effective CAL material that overcomes long-standing interfacial limitations in dopant-free tandem OLEDs, providing a practical pathway toward highly efficient and color-pure next-generation displays.

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