Switchable interfacial reaction enables bright and stable deep-red perovskite light-emitting diodes

High-performance deep-red light-emitting diodes (LEDs) are important for biomedical and agricultural applications. However, the development of bright and stable solution-processed deep-red LEDs remains challenging. Here we design a switchable interfacial deprotonation reaction between the perovskite and electron-transporting layer to fabricate high-quality CsPbI₃ perovskite films, leading to stable and bright deep-red LEDs. Our approach starts with a precursor solution containing guanidine hydroiodide and a layer of alkaline zinc hydroxide. On annealing, the interfacial reaction is switched on, leading to the formation of high-quality CsPbI₃. The alkaline zinc hydroxide layer is simultaneously converted in situ to alkalescent ZnO, which prevents the formation of the undesirable yellow-phase CsPbI₃ perovskite. As a result, our perovskite LEDs based on CsPbI₃ demonstrate a long half-lifetime of approximately 33.6 h under a driving current density of 100 mA cm^–2 and an exceptionally high radiance of around 1,980 W sr⁻¹ m^–2. Moreover, by partly substituting iodide with bromide, we achieve bright deep-red perovskite LEDs with an emission wavelength of 691 nm and an operational half-lifetime of 50.3 h at 100 mA cm^–2.