Fig. 1. Strategies for improving the performance of perovskite LED^[3-5]

Fig. 2. Structure of near-infrared perovskite LEDs and dimensional control. (a) Band energy level diagram of perovskite LED structure^[3]; (b) schematic of cascade energy transfer in multiple quantum wells (MQWs) perovskite^[4]; (c) excitation-intensity-dependent PLQE of MQWs film^[4]; (d) schematic of charge recombination in MQWs with different well widths^[25]

Fig. 3. Near-infrared three-dimensional perovskites. (a) Grain distribution in perovskite films with different concentration^[27]; (b) structure and performance of top-emitting perovskite LED^[28]; (c) schematic of device structure and light output with submicrometre-structured perovskite film^[5]; (d) operation stability of devices at 45 K with a constant current density of 200 mA·m^{-2 [29]}; (e) schematic of growth pathways of perovskites with different additives^[30]

Fig. 4. Red, green,and blue perovskites. (a) Schematic showing the red perovskite LED structure^[35]; (b) mechanism of γ-CsPbI₃ formation process on ZnO substrate^[36]; (c) schematic of 2D perovskite films with various organic cations^[37]; (d) organic cations with various dipole moments and MQWs structure of quasi-2D perovskite^[38]; (e) schematic of in situ fabrication process of perovskite nanocrystal films^[39]; (f) schematic of phase homogenization process of mixed-halide perovskite through the assistance of Tween and TPPB^[40]

Fig. 5. Lead free perovskites. (a) Schematic of (PEAI)_x(CsI)_y(SnI₂)_z MQWs perovskite^[46]; (b) schematic of copper halide emitter material and EL spectra of the device under different voltages^[49]