All-Inorganic CsPbI₃ Perovskite Phase-Stabilized by Poly(ethylene oxide) for Red-Light-Emitting Diodes

Despite the excellent photoelectronic properties of the all-inorganic cesium lead iodide (CsPbI₃) perovskite, which does not contain volatile and hygroscopic organic components, only a few CsPbI₃ devices are developed mainly owing to the frequent formation of an undesirable yellow δ-phase at room temperature. Herein, it is demonstrated that a small quantity of poly(ethylene oxide) (PEO) added to the precursor solution effectively inhibits the formation of the yellow δ-phase during film preparation, and promotes the development of a black α-phase at a low crystallization temperature. A systematic study reveals that a thin, dense, pinhole-free CsPbI₃ film is produced in the α-phase and is stabilized with PEO that effectively reduces the grain size during crystallization. A thin α-phase CsPbI₃ film with excellent photoluminescence is successfully employed in a light-emitting diode with an inverted configuration of glass substrate/indium tin oxide/zinc oxide/poly(ethyleneimine)/α-CsPbI₃/poly(4-butylphenyl-diphenyl-amine)/WO₃/Al, yielding the characteristic red emission of the perovskite film at 695 nm with brightness, external quantum efficiency, and emission band width of ≈101 cd m⁻², 1.12%, and 32 nm, respectively.