A review on lanthanide-based materials as dopants and buffer layers in organic light-emitting diodes: photophysical properties and device performance

Abstract Organic light-emitting diodes (OLEDs) offer lucrative advantages in screening and illuminating technologies, including high luminance, design flexibility and energy efficiency. However, commercial adoption is hindered by challenges like device degradation and efficiency roll-off, especially under thermal and electrical stress. This review focuses on the application of lanthanide-based materials in OLEDs, emphasizing their unique photophysical properties and roles as emissive dopants and buffer layers. Lanthanide complexes such as europium(III), samarium(III), terbium(III) and cerium(III) possess unique photophysical properties that enhance exciton confinement, reduce polaron–exciton annihilation and improve radiative efficiency. Ligand systems, including β-diketonates, phenanthroline derivatives, scorpionate frameworks and boron-containing ligands, further support high triplet-energy transfer, improved solubility and efficient charge balance within host–dopant architectures. Europium-based emitters demonstrate reduced roll-off and improved luminance. Additionally, cerium(III) complexes show ultrafast excited-state lifetimes and near-unity quantum yields. Metal alloys incorporating ytterbium and its oxides act as superior buffer layers in cathodes that can inhibit the penetration of moisture and oxygen, enhancing both transparency and lifetime. Yb-based cathodes and interlayers, especially in combinations like Yb/Ag or LiF/Yb/Ag, enable efficient electron injection and mitigate degradation through improved stability. These innovations collectively address core issues in OLED performance, laying the foundation for highly durable, high-brightness and flexible optoelectronic devices.