Fig. 1. Preliminary study of pure 3D perovskites and their blue PeLEDs. (a) Schematic diagram of the structure of 3D perovskites. (b) Photoluminescence spectra of MAPb(Br_1−xCl_x)₃ perovskite film with different ratios of Cl^-. (c) SEM image of MAPb(Br_1−xCl_x)₃ perovskite film on ITO/PEDOT:PSS substrate. (d) Normalized EL spectra of CH₃NH₃Pb(Br_xCl_1−x)₃ [0 ≤ x ≤ 1] perovskite thin-film-based LEDs with different chloride−bromide ratios, as indicated and measured at 77 K. Figure reproduced with permission from: (a-c) ref.³⁵, American Chemical Society; (d) ref.³⁶, American Chemical Society.

Fig. 2. Morphology and PLQY modification for 3D perovskites and their blue PeLEDs. (a) The calculated coverage degree and average grain size of perovskite films with various CsBr:RbBr molar ratios. (b) EL spectra of the device fabricated with cocktail cation strategy operating under different voltages. The inset shows a digital photograph of a device in operation. (c) PLQY measurements with various Mn doping ratios. (d) Time-resolved photoluminescence (TRPL) decays of samples A (deep-blue region), B (blue region), and C (sky-blue region). Figure reproduced with permission from: (a) ref.³⁹, Royal Society of Chemistry; (b) ref.⁴⁰, American Chemical Society; (c) ref.⁴¹, American Chemical Society; (d) ref.⁴², American Chemical Society.

Fig. 3. Spectral tuning strategies for PQDs and their blue PeLEDs. (a) Schematic diagram of CsPbBr_xCl_3-x QD-based blue PeLED device structure by the DDAB/DDAC post-treatment strategy. (b) EL spectra of CsPbBr_xCl_3−x QD-based PeLEDs with various ratios of DDAB and DDAC in precursor solution. The inset shows a digital photograph of the device in operation. (c) Schematic diagram of the halogen exchange process in PQDs enhanced by benzenesulfonates. Figure reproduced with permission from: (a) ref.⁵³, American Chemical Society; (b) ref.⁵⁴, American Chemical Society; (c) ref.⁵⁵, American Chemical Society.

Fig. 4. Defects passivation strategies for PQDs and their blue PeLEDs. (a) TRPL curves of pristine, RbBr-modified, and FABr/RbBr-modified PQD films. (b) PLQY of Ni²⁺ ion-doped CsPbCl_xBr_3−x PQDs in dispersion with NiCl₂ precursor feeding amounts of 0, 0.01, 0.02, 0.04, and 0.08 ml. The inset shows photographs of the Ni²⁺ ion-doped CsPbCl_xBr_3−x PQDs under 365 nm UV lamp illumination. (c) Illustration of Cl vacancy-induced trap site formation, electron trapping, and self-assembly of DAT on the defect sites of perovskite films. (d) EL spectra of Cs₃Cu₂I₅ QD-based PeLEDs measured before aging, after running for 108 and 170 h, and after a relaxation time of 1 h. Figure reproduced with permission from: (a) ref.⁶³, Royal Society of Chemistry; (b) ref.⁶⁵, American Chemical Society; (c) ref.⁶⁸, American Chemical Society; (d) ref.⁷⁰, American Chemical Society.

Fig. 5. Dimension tuning and surface passivation strategies for PNLs and their blue PeLEDs. (a) A digital photograph of the first colloidal PNL-based pure-blue LED in operation (area: 3 mm × 5 mm). (b) Schematic diagram of colloidal NPLs treated by DDAB. (c) EL spectra of the colloidal PNL-based PeLEDs fabricated by Bohn et al. with PbBr₂ post-treatment strategy. The inset shows digital photographs of a device in operation. (d) Illustration of in-situ passivation strategy of PbBr₆⁴⁻ octahedra. Figure reproduced with permission from: (a) ref.⁷⁴, American Chemical Society; (b) ref.⁷⁵, American Chemical Society; (c) ref.⁷⁶, American Chemical Society; (d) ref.⁷⁸, American Chemical Society.

Fig. 6. Phases modulation strategies for quasi-2D perovskite and their PeLEDs. (a) EL spectra of BA cations-based quasi-2D PeLEDs. (b) PLQY and trap density curves of quasi-2D perovskite film with various concentration of PEABr. (c) PL spectra of Rb-Cs alloyed perovskite films with various composition. (d) Transient absorption spectra of PEA₂MA_1.5Pb_2.5Br_8.5 with various molar ratio of IPABr from 0 to 40%. Figure reproduced with permission from: (a) ref.⁸⁵, American Chemical Society; (b) ref.⁸⁷, Springer Nature; (c) ref.⁸⁹, Springer Nature; (d) ref.⁹¹, Springer Nature.

Fig. 7. Spectral stability modification strategies for quasi-2D perovskite and their PeLEDs. (a) Schematic diagram of the yttrium gradient distribution in the CsPbBr₃:PEACl (1:1) film and its function in increasing the bandgap around the grain surface. (b) Stable EL spectra of DPPOCl-treated PeLEDs before and after operation. The inset is the schematic diagram of the mechanism of the DPPOCl induced chlorides-insertion-immobilization process. (c) EL spectra of moisture-treated blue emissive device operated under a different bias with moral ratio of CsBr: PbBr₂ of 2.2. Figure reproduced with permission from: (a) ref.⁹⁸, Springer Nature; (b) ref.⁹⁹, American Chemical Society; (c) ref.¹⁰⁴, American Chemical Society.

Fig. 8. Interface modification strategies for blue PeLEDs. (a) Device structure of quasi-2D blue PeLEDs with LiF as the interface modification layer. (b) Energy level alignment diagram of blue PeLEDs with device structure of LiF-perovskite-LiF. (c) Device structure and (d) cross-section picture of quasi-2D PeLEDs with RbCl as the interface modification layer. Figure reproduced from: (a) ref.⁸⁶, American Chemical Society; (b) ref.⁴⁰, American Chemical Society; (c) and (d) ref.¹¹⁰, American Chemical Society.

Fig. 9. Energy level alignments of various ETL, HTL, and emissive layer materials.

Table 1. Summary of the main blue PeLEDs.