Sequential layer-by-layer deposition for high-performance fully thermal-evaporated red perovskite light-emitting diodes

Thermal-evaporated perovskite light-emitting diodes are highly promising for future display and lighting. However, multi-source co-evaporation faces challenges such as difficulty in regulating crystallinity, especially for red perovskite light-emitting diodes, whose external quantum efficiencies are still less than 2%. Here, we demonstrate a facile layer-by-layer thermal-evaporation strategy to fabricate high-quality perovskite-emitting films with tunable emission wavelengths. 5-Aminovaleric acid is introduced to regulate interfacial reactions during deposition, slow down crystallization during post-annealing, and passivate defects through coordination interactions. This approach yields perovskite emitting layers with high uniformity and luminance efficiency. As a result, red (670 nm) and deep-red (730 nm) perovskite light-emitting diodes achieve maximum external quantum efficiencies of 9% and 7.27%, and luminance of over 1500 cd m^-2 and 200 W s^-1 m^-2, respectively. Furthermore, large-area (2500 mm²) and patterned perovskite thin films and light-emitting diodes with outstanding uniformity are successfully demonstrated.