Fig. 1. ABX₃ metal halide perovskite general crystal structure. (a) A-type cations occupy lattice corners, B-type cations occupy interstitial sites, and X-type anions occupy lattice face centers; (b) B-type cations cluster around X-type anions to form [BX₆]⁴⁻ structures^[27-28]

Fig. 2. (a) Schematic of quasi-2D perovskite structure; (b) Schematic of energy funnel effect^[32]

Fig. 3. (a) Device structure of PeLEDs; (b) Energy level alignment of PeLEDs^[13]

Fig. 4. Schematic of interface and region of exciton generating for (a) PeLEDs (n=1); (b) Optimized PeLEDs (n=4). Black solid line represents the interface for exciton generation, and red dashed box represents the region for exciton generation^[14]

Fig. 5. (a) Schematic of PeLEDs device structure; (b) Energy level alignment of PeLEDs^[15]

Fig. 6. Exciton interface recombination effect. (a) PEDOT: PSS/CsPbBr₃; (b) PEDOT: PSS/TAPC/CsPbBr₃^[15]

Fig. 7. (a) Energy level alignment of PeLEDs; (b) Schematic of exciton energy transfer mechanism in FIrpic: CsPbBr₃^[16]

Fig. 8. Diagram of exciton energy transfer mechanism in TmPyPB:FIrpic: CsPbBr₃ film (red solid arrow indicates Förster energy transfer process, dashed arrow indicates Dexter energy transfer process)^[17]

Fig. 9. Schematic of energy transfer processes between the CsPbBr₃ emission layer and the TmPyPB: FIrpic composite exciton blocking layer(dashed arrows indicate Dexter energy transfer and solid arrows indicate Förster energy transfer)^[18]

Fig. 10. Molecular structure of thermally activated delayed fluorescence materials (TADF). (a) 2CzPN (traditional TADF); (b) Cz-3CzCN (TADF dendrimer); (c) Cz-4CzCN (TADF dendrimer); (d) t-DABNA-dtB (TADF dendrimer); (e) P-Cz5CzCN (TADF polymer)^[19-24]

Fig. 11. Schematic diagram of energy transfer mechanism in CsPbBr₃: 2CzPN film^[19-20]

Fig. 12. Schematic diagram of energy transfer mechanism between PEA₂Cs_n−1Pb_nBr_3n+1 and Cz-3CzCN^[21-22]

Fig. 13. Schematic diagram of phase distribution, carrier transport, and exciton radiative recombination in blue PeLEDs based on (a) PVK and (b) PVK: t-DABNA-dtB as HTLs^[23]

Fig. 14. (a) Schematic diagram of the distribution of the perovskite, additives, traps and grain boundary; (b) Schematic diagram of charge injection, exciton recombination, and energy transfer mechanism in luminescent thin films^[24]