Interface permanent dipoles induced by atomic layer deposited Al2O3 for high-performance perovskite light-emitting diodes

The deposition of charge blocking layer (CBL) has been proved as an essential approach to improve the unbalanced charge injection and enhance the external quantum efficiency (EQE) of perovskite light-emitting diodes (PeLEDs). Nonetheless, in near-infrared (NIR) PeLEDs, the CBL covering on the typical ZnO electron transport layer (ETL) usually affects the deprotonation process and thereby decreases the crystallinity of perovskite film. In this work, we improve the performance of PeLEDs by atomic layer deposition (ALD) of an ultra-thin (0.43 nm) aluminum oxide (Al 2 O 3 ) CBL between the ETL ZnO and perovskite layer. This CBL improves the charge injection balance and optimizes the morphological and crystalline characteristics of perovskite film. The NIR PeLEDs achieve a peak EQE of 17.0 % with the optimal Al 2 O 3 CBL, representing a 25 % enhancement compared to the control device. In particular, with in-situ electroabsorption (EA) spectroscopy, we discover that the presence of interface permanent dipoles ascribed to the ultra-thin Al 2 O 3 CBL, facilitates the charge injection balance by greatly increasing the built-in potential and reducing the electron injection. Hence, this work paves a practical way to enhance the efficiency of NIR PeLEDs without influencing the deprotonation process.