Fig. 1. (Color online) (a) Diagram of 3D perovskite crystal structure^[71]. (b) Schematics of crystal structure and multiple quantum wells structure of 2D/quasi-2D perovskite with different n value. Energy can rapidly and efficiently funnel from wide bandgap phase to narrow bandgap phase^[72]. (c) Bandgap of CsPbX₃ NCs, X = Cl, Cl/Br, Br, Br/I or I. Reproduced with permission from Ref. [65]. Copyright 2016, American Chemical Society. (d) Emission wavelength of CsPbX₃ NCs. (e) Color gamut of combination of red, green and blue CsPbX₃ NCs emitters (black triangle) on CIE chromatic coordinates compared to LCD (white dashed triangle) and NTSC TV (white solid triangle) standards. (d) and (e) are reproduced with permission from Ref. [14]. Copyright 2015, American Chemical Society. (f) Diagram of defect tolerance of conventional semiconductor and perovskites. Reproduced with permission from Ref. [73]. Copyright 2017, American Chemical Society. (g) Young’s modulus of MAPbX₃ single crystals versus Pb−X bond strength, X = Cl, Br or I. Reproduced with permission from Ref. [74]. Copyright 2015, Royal Society of Chemistry. (h) Young’s modulus of APbX₃ single crystals versus Pb−X bond distance, A = MA or FA and X = Cl, Br or I. Reproduced with permission from Ref. [75]. Copyright 2017, Wiley−VCH. Out-of-plane elastic modulus of 2D/quasi-2D single crystal perovskites with different (i) B−X bond, (j) n value, (k) length of alkyl chains and (l) species of organic spacers. (i) and (l) are reproduced with permission from Ref. [76]. Copyright 2020, American Chemical Society. (j) and (k) are reproduced with permission from Ref. [77]. Copyright 2018, American Chemical Society. (m) Stress-strain curve of single crystal and polycrystalline perovskites with different grains amounts under tensile loading. Extensively amorphous occurs in polycrystalline perovskites during yielding process. Reproduced with permission from Ref. [78]. Copyright 2016, American Chemical Society.

Fig. 2. (Color online) (a) Diagram of FPeLEDs device structure. (b) Schematic of the synergetic effect of PEABr and PEG on modulating crystallization. (c) SEM images of perovskite films with composition of CsPbBr₃ and CsPbBr₃/PEG/PEABr. (b) and (c) are reproduced with permission from Ref. [86]. Copyright 2018, Wiley−VCH. (d) SEM images of perovskite QDs films without and with PVP. (e) PLQY of perovskite QDs films with PVP under different exciting intensities. (d) and (e) are reproduced with permission from Ref. [87]. Copyright 2020, Elsevier. (f) SEM images of perovskite films depositing on pristine and ETA-modified PEDOT:PSS films. Reproduced with permission from Ref. [46]. Copyright 2020, American Chemical Society. (g) Schematic of mechanism of passivation KI layer between HTL and EML. Reproduced with permission from Ref. [85]. Copyright 2022, American Chemical Society. (h) Schematic of encapsulation growth method. (i) Comparison of energy transfer between control and modified perovskite films grown by encapsulation growth method. (h) and (i) are reproduced with permission from Ref. [88]. Copyright 2021, Elsevier. (j) Schematics of the N₂-asisted spin-coating method. Reproduced with permission from Ref. [89]. Copyright 2019, Wiley−VCH. (k) Schematics of the mechanism of flash light annealing. (l) Maximum CE of devices using thermal annealing and flash light annealing under different energy density. (k) and (l) are reproduced with permission from Ref. [31]. Copyright 2019, Elsevier.

Fig. 3. (Color online) (a) SEM images of different perovskite films without and with 2.5 wt% PEO before and after stretching. (b) PL intensity of perovskite film with 2.5 wt% PEO after tensile tests. (a) and (b) are reproduced with permission from Ref. [44]. Copyright 2019, Elsevier. (c) PL intensity of EC-treated perovskite films as a function of bending cycles at a curvature radius of 3 mm. EL luminance of EC-treated perovskite films as a function of curvature radius. Reproduced with permission from Ref. [130]. Copyright 2022, WILEY-VCH. (d) Cohesion energy and PLQY of control, BAI, DDAI, PMAI, PEAI and FPMAI-modified perovskite films. (e) Normalized EQE of FPMAI-modified perovskite films as a function of bending cycles at a curvature radius of 1 and 2 mm. Normalized EQE of perovskite films modified by different additives as a function of curvature radius. (d) and (e) are reproduced with permission from Ref. [34]. Copyright 2018, WILEY-VCH. (f) Schematic of self-healing ability of perovskite films with MDI-PU. (g) SEM images of perovskite films with and without MDI-PU before and after annealing. (f) and (g) are reproduced with permission from Ref. [45]. Copyright 2022, American Chemical Society. (h) Schematic of self-healing ability of perovskites/fluoroelastomer composite films through strong dipole-dipole interaction between -CF₃ groups. (i) Images of broken perovskites/fluoroelastomer composite films during self-healing process. (j) Normalized PL intensity of perovskite/fluoroelastomer composite films after different mechanical tests. (h)−(j) are reproduced with permission from Ref. [131]. Copyright 2022, WILEY-VCH. (k) Schematic of fabrication of perovskite/polymer composite nanofibers membrane through electrospinning. Reproduced with permission from Ref. [132]. Copyright 2019, American Chemical Society. (l) Images of perovskite/polymer composite nanofibers membrane emitting bright white light under 365 nm ultraviolet irradiation before and during stretching. Reproduced with permission from Ref. [133]. Copyright 2018, American Chemical Society.

Fig. 4. (Color online) Comparison of advantages and disadvantages between various conductive materials. Reproduced with permission from Ref. [148]. Copyright 2020, WILEY-VCH.

Fig. 5. (Color online) (a) Image of the fully printed FPeLED emitting bright green light at a bending state with a curvature radius of 5 mm. Reproduced with permission from Ref. [40]. Copyright 2015, American Chemical Society. (b) Normalized CE of FPeLEDs based on ITO and graphene anodes as a function of bending strain and cycles. Reproduced with permission from Ref. [43]. Copyright 2017, WILEY-VCH. (c) Normalized sheet resistance of PEDOT:PSS with and without PEO films as a function of tensile strain. Reproduced with permission from Ref. [44]. Copyright 2019, Elsevier. (d) Luminance variation of FPeLEDs based on PEDOT:PSS/DMSO/Zonyl electrodes as a function of operation time and bending cycles at a curvature radius of 1.0 or 2.5 mm. Reproduced with permission from Ref. [94]. Copyright 2019, American Chemical Society. (e) Diagram of FPeLEDs based on photopatterned PEDOT:PSS anodes. Reproduced with permission from Ref. [159]. Copyright 2023, American Chemical Society. (f) Schematic of mechanism of tunable work function AnoHIL^[162]. (g) Resistance of PI/AgNWs as a function of stretch-release counts. Reproduced with permission from Ref. [106]. Copyright 2019, WILEY-VCH. (h) Sheet resistance of AgNWs/H₂SO₄-treated PEDOT:PSS composite electrodes (left) and luminance of corresponding FPeLEDs as a function of bending cycles at a curvature radius of 2.5 mm. (i) Images of FPeLEDs based on AgNWs/H₂SO₄-treated PEDOT:PSS composite anodes emitting bright light at different bending states. (h) and (i) are reproduced with permission from Ref. [39]. Copyright 2019, American Chemical Society. (j) Cross-sectional HRTEM image of Ag-Ni core-shell NWs composite electrodes. Reproduced with permission from Ref. [98]. Copyright 2020, American Chemical Society. (k) Resistance of different composite electrodes samples. Sample 1, 2 and 3 stand for AgNWs/AgNPs, AgNWs/AgNPs/PEDOT:PSS and AgNWs/AgNPs/PEDOT:PSS/MXenes composite electrodes, respectively. (l) Normalized resistance (left) and EQE (right) as a function of bending cycles at a curvature radius of 1 cm. (k) and (l) are reproduced with permission from Ref. [97]. Copyright 2022, American Chemical Society.

Fig. 6. (Color online) (a) Energy band structure of bi-HTLs FPeLEDs. Reproduced with permission from Ref. [91]. Copyright 2017, Royal Society of Chemistry. (b) Energy band structure of FPeLEDs using Buf-HTL. Reproduced with permission from Ref. [43]. Copyright 2017, WILEY-VCH. (c) Energy band structure of FPeLEDs using PEDOT:PSS HTL modified by different contents of Zonyl. Reproduced with permission from Ref. [39]. Copyright 2019, American Chemical Society. (d) Energy band structure of FPeLEDs using pristine, IPA and PSS-Na-modified PEDOT:PSS HTL. Reproduced with permission from Ref. [99]. Copyright 2020, Elsevier. (e) Schematic of perovskite films with dendritic structure. Reproduced with permission from Ref. [171]. Copyright 2021, WILEY-VCH. (f) Energy band structure of FPeLEDs adopting perovskite/CDs composite films. Reproduced with permission from Ref. [172]. Copyright 2021, WILEY-VCH.

Fig. 7. (Color online) (a) Schematic of fabrication process of FPeLEDs with patterned electrodes. Reproduced with permission from Ref. [159]. Copyright 2023, American Chemical Society. (b) Schematic of pixelated FPeLEDs arrays prepared by double-layer transfer printing technique. (c) EL images of ultrathin skin-attachable displays attached to human skin, leaf and edge of blade. (d) EL images of ultrathin skin-attachable displays under 20% compression, twists and water droplet^[107]. (e) Schematic of writable and wipeable FPeLEDs^[109]. (f) EL images of writable and wipeable FPeLEDs before and after wiping^[109]. (g) Schematic of mechanism of flexible perovskite LETDs. Reproduced with permission from Ref. [90]. Copyright 2017, American Chemical Society. (h) Schematic of mechanism of ECG monitor using multi-color FPeLEDs. Reproduced with permission from Ref. [122]. Copyright 2021, American Chemical Society.