Vacuum Thermal Evaporation for OLEDs: Fundamentals, Optimization, and Implications for Perovskite LEDs

Organic light‐emitting diodes (OLEDs) are central to high‐end displays and solid‐state lighting due to their small thickness and high flexibility, wide color gamut, and low power consumption. While solution processing offers simplicity and cost advantages for polymer‐based OLEDs, vacuum thermal evaporation (VTE) remains the dominant method for the commercial production of high‐performance small‐molecule OLEDs, owing to its precise control over film thickness, material purity, and multilayer integration. However, to meet the demands of display applications for higher performance, lower cost and more diverse forms (such as flexibility and high resolution), it is crucial to continuously optimize the VTE process. Meanwhile, although solution processing remains the predominant approach for perovskite light‐emitting diodes (PeLEDs), recent exploratory efforts have investigated VTE as an alternative route, thereby opening opportunities to transfer process insights from OLEDs to PeLEDs. This review aims to systematically summarize the application foundation and optimization strategies of VTE technology in OLEDs, and to explore how these mature practices can inform the process development and device design of vacuum‐evaporated PeLEDs.