Vacuum-Evaporated, Lead-Free RbYbI(3) Perovskite Interlayers for Universal Electron Injection in High-Performance Organic Light-Emitting Diodes.

The optoelectronic performance of organic light-emitting diodes (OLEDs) is critically governed by charge injection from electrodes into organic layers, where significant energy barriers at the interfaces often impede efficient charge injection. These barriers disrupt the balance between hole and electron injection in the emitting layer, thereby limiting device optoelectrical performance. Conventional electron injection layers (EILs), such as lithium fluoride (LiF) or ultrathin metal layers, often exhibit limited injection efficiency when used with certain metals, including silver. In this work, we propose a lead-free perovskite thin film, RbYbI, as an efficient EIL for OLEDs. Deposited via vacuum evaporation, a 5-nm-thick RbYbI layer induces a 630-mV surface potential shift at the interface between the organic layer and the metal electrode. First-principles density functional theory calculations also confirm that RbYbI exhibits termination-dependent surface dipole formation, thereby lowering the effective injection barrier relative to LiF. This facilitates efficient electron injections across various organic semiconductors without requiring additional interface engineering. Furthermore, RbYbI is compatible with both aluminum and silver cathodes, unlike LiF, which exhibits electrode-material limitations. When applied to blue-emitting OLEDs, the device with RbYbI exhibits a lower turn-on voltage by 0.4 V and a higher external quantum efficiency (EQE) of 19.5% than the control using LiF (EQE of 17.7%). Similarly, green OLEDs with RbYbI maintained superior efficiency at high luminance, with a maximum EQE of 23.0% and 20.7% at 10 000 cd m , compared to 22.0% and 15.8% at 10 000 cd m for the LiF-based control device. The perovskite-based EIL is readily integrated into standard OLED fabrication processes, providing a universal and practical strategy to overcome the limitations of conventional EILs and enabling the development of high-performance OLEDs.