Efficient All-Inorganic Perovskite Light-Emitting Diodes with Improved Operation Stability

Stability is becoming a main issue for perovskite light-emitting diodes (PeLEDs), as their external quantum efficiency (EQE) has been boosted to above 20%. An all-inorganic perovskite, cesium lead iodide (CsPbI₃), has better stability than organic–inorganic hybrid perovskites but suffers from a transition to yellow δ-CsPbI₃ phase at room temperature. Herein, we report stabilization of the α-CsPbI₃ phase by in situ formation of perovskite nanocrystals (NCs). By incorporation of a proper ratio of bulky organoammonium halides, 4-fluoro-phenylmethylammonium iodide (4-F-PMAI), stable α-CsPbI₃ films with nanometer-sized crystals can be obtained using a one-step spin-coating approach. The PeLEDs using α-CsPbI₃ NC films as emitters show a pure red emission at 692 nm and a high EQE of 14.8%. The EQE is further boosted to 18.6% using CsPbI_2.8Br_0.2 as the emissive layer. Furthermore, the PeLEDs show a very decent half-lifetime of over 1200 min and a shelf stability of over 2 months, much longer than that of hybrid PeLEDs.