A Mixed Organic-Inorganic Interlayer with Tunable Electrical Properties Enabling Stable and Efficient Perovskite Light-Emitting Diodes

The operational stability of perovskite light-emitting diodes (PeLEDs) is subjected to undesired Joule heating induced by the charge imbalance and the current leakage. The hole injection efficiency is inferior to that of electrons in the electron-dominated PeLEDs, owing to the low hole mobility of hole transport materials and a relatively large hole injection barrier. Herein, we inserted a mixed interlayer of 4,7-diphenyl-1,10-phenanthroline and cesium carbonate (Bphen:Cs 2 CO 3 ) (~10 nm) between the electron transport layer (ETL) TPBi and the metal cathode to improve the charge imbalance by optimizing the electron injection and suppressing the current leakage. Compared to TPBi, the Bphen interlayer builds a larger electron injection barrier from the cathode to perovskite layer owing to its shallower lowest unoccupied molecular orbital (LUMO), leading to inefficient electron injection. The Cs 2 CO 3 , an n-type dopant, was co-evaporated with Bphen to increase the conductivity and thus balance the electron and hole transport. The resultant quasi-2D PeLED achieves an external quantum efficiency of 17.62% and an operational lifetime of over 1900 min at an initial luminance of 100 cd m -2 .