Large‐Area Flexible Perovskite Light‐Emitting Diodes Enabled by Inkjet Printing

Abstract Metal halide perovskite light‐emitting diodes (PeLEDs) are attracting increasing attention due to their potential applications in flat panel lighting and displays. The solution process, large‐area fabrication, and flexibility are attractive properties of PeLEDs over traditional inorganic LEDs. However, it is still very challenging to deposit uniform perovskite films on flexible substrates using a blade or slot‐die coating, as the flexible substrate is not perfectly flat. Here, the inkjet printing technique is adopted, and the key challenges are overcome step‐by‐step in preparing large‐area films on flexible substrates. Double‐hole transporting layers are first used and a wetting interfacial layer to improve the surface wettability so that the printed perovskite droplets can form a continuous wet film. The fluidic and evaporation dynamics of the perovskite wet layer is manipulated to suppress the coffee ring effect by solvent engineering. Uniform perovskite films are obtained finally on flexible substrates with different perovskite compositions. The peak external quantum efficiency of the inkjet‐printed PeLEDs reaches 14.3%. Large‐area flexible PeLEDs (4 × 7 cm²) also show very uniform emission. This work represents a significant step toward real applications of large‐area PeLEDs in flexible flat‐panel lighting.