Fig. 1. Schematic diagram of working mechanism and stability factors of PeLED devices

Fig. 2. Schematics of perovskite crystal structure, common defects and strategies^[63]

Fig. 3. Schematics of crystallization regulation mechanism. (a) BMCl regulating crystallization process^[81]; (b) SEM morphology without additives^[81]; (c) SEM topography with addition of BMCl^[81]; (d) schematic diagram of effect of ABA on perovskite and interaction between adjacent perovskite layers in ABA-doped perovskite^[83]; (e) schematic diagram of crystal structure of perovskite films^[89]; (f) schematic diagram of interlayer structures of (PEA) ₂PbI₄, (PEA) (NMA) PbI₄ ,and (NMA) ₂PbI₄^[92]

Fig. 4. Mechanism diagram and auxiliary proof for defect passivation in different methods. (a) Surface configuration after relaxation^[26]; (b) differential charge density plot of SFB10^[26]; (c) schematic diagram of passivation of perovskite grain boundary defects by FPMATFA^[48]; (d) ATR-FTIR spectra of FAI, EDEA, and FAI and EDEA mixtures^[96]; (e) theoretical calculation of electron distribution (maximum valence band) of HMDA and EDEA^[96]; (f) 1H NMR spectra of FAI containing 15% (mass fraction)EDEA or HMDA in DMSO and FAI ^[96]

Fig. 5. Interface modification and mechanism. (a) ETA interface modification diagram^[97]; (b) internal model diagrams of device after current injection under different conditions^[103]

Fig. 6. Band structure regulation and charge transfer. (a) Stepped injection level between PEDOT∶PSS and perovskite^[52]; (b) EQE-J curves of devices with different structures^[52]; (c) adjustment effect of different additives on perovskite work function^[112]; (d) schematic of surface coordination of SO-DMAc onto Pb²⁺ of perovskite and electron transfer from SO-DMAc to perovskite^[31]; (e) UPS spectra of high binding energy secondary-electron cutoffs and valence-band edge regions of nickel oxide and nickel oxide/SBTI films^[113]

Fig. 7. Inhibition and resolution of ion migration. (a) Schematic diagram of Ni doping inhibition of ion migration^[115]; (b) proton transfer reaction between MA and BnA^[118]; (c) schematics of possible ion migration pathways in 3D and 3D/2D hybrid perovskites and effective restriction of ion migration by BnA which has effect of blocking redirection^[118]; (d) in-depth analysis of time-of-flight secondary ion mass spectrometry (ToF-SIMS) on NMAI devices (initial, semi-degraded, recovered, and fully degraded) and display of I^-, Au⁺, and CH3- ions^[75]; (e) (f)XPS surface element characterizations of perovskite films of ODEA devices (initial, semi-degraded, and restored) ^[75]

Fig. 8. Investigation of Joule heat and its effect on devices. (a) Surface temperature distributions of PeLED based on glass and sapphire substrates at different voltages^[52]; (b) schematics of flat and patterned PeLED performance improvement mechanisms with photon trajectories shown by arrows ^[58]; (c) relationship between optical power distribution of MAPbI₃ PeLED and thickness of perovskite luminous layer^[120]; (d) lifetime of doped and undoped PeLED at constant current density of 10 mA·cm^{-2 [121]}; (e) external quantum efficiency-current density (EQE-J) curves of PeLED on glass or sapphire substrates^[121]; (f) EQE-J curve of PeLED on sapphire substrate^[121]