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

The stability is becoming a main issue for perovskite light emitting diodes (PeLEDs) as their external quantum efficiency (EQE) has been boosted to above 20%. 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 α-CsPbI3 phase by in-situ formation of perovskite nanocrystals. 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 nanocrystal films as emitter show a pure red emission at 692 nm and a high EQE of 14.8%. The EQE is further boosted to 18.6% using CsPbI2.8Br0.2 as emissive layer. Furthermore, the PeLEDs show very decent half-lifetime of over 1,200 min and shelf stability of over 2 months, much longer than that of hybrid PeLEDs.