Performance boosting strategy for perovskite light-emitting diodes

Low-dimensional (low-D) luminescent materials have attracted significant attention due to the high photoluminescent quantum yields. However, it is unclear whether low-D materials are superior to 3D materials for electroluminescent (EL) devices given that low-D materials have poor charge transport nature due to their highly localized electronic structures. We noticed a significant phenomenon that EL performances for 3D materials, such as CsPbX3, are governed by adjacent charge transport layers, which is possibly due to nonradiative recombination resulting from the small exciton binding energy. This finding encouraged us to develop new electron transport layers (ETLs) that satisfy not only the energy alignment to confine excitons but also an efficient electron injection into 3D CsPbX3 layers. This strategy enables one to exploit the good charge transport nature of 3D CsPbX3. The proposed amorphous Zn-Si-O ETL has sufficiently shallow electron affinity (∼3.2 eV) to confine excitons and sufficiently high electron mobility (∼0.8 cm2/V s) to transport electrons. Furthermore, the controllable conductivity and electron affinity of amorphous Zn-Si-O enable fine-tuning of charge balance. Consequently, the very low operating voltage of 2.9 V at 10 000 cd/m2 and high power efficiency of 33 lm/W were achieved for a green perovskite (CsPbBr3) EL (PeLED). The obtained ultrahigh brightness of ∼500 000 cd/m2 demonstrates the effectiveness of the proposed strategy. We also extend this strategy into 3D CsPbBrI2 (red) and 3D CsPbBrCl2 (blue) PeLEDs, and demonstrate a record high brightness of 20 000 cd/m2 for the red PeLED. We believe this study provides new insight into the realization of practical PeLEDs.