Fig. 1. (a) Microscopic image of an MAPbI3 laser operating at a pump intensity of 1.1Pth (26.1  μJ/cm2) after working for different times. (b) Lasing stability data of MAPbI3 laser under femtosecond laser pumping with a repetition rate of 6 kHz in ambient air condition. (c) Spectrum evolution of MAPbI3 laser operating at a pump intensity of 1.1Pth (26.1  μJ/cm2) after working for different times. (d) Microscopic image of the nanoplatelet after operating for 1800 s. (e) Microscopic image and SEM image of the initial MAPbI3 nanoplatelet with surface defects. (f) Atomic force microscopic image of the MAPbI3 nanoplatelet shows that its RMS roughness is 2.1 nm.

Fig. 2. (a) Microscopic image of MAPbI3 nanoplatelets on a mica substrate. (b) XRD pattern of the MAPbI3 nanoplatelets. (c) Microscopic image of an MAPbI3 nanoplatelet used for demonstrating the laser before exposure to a pump laser. (d) SEM image of MAPbI3 nanoplatelet. (e) AFM image of MAPbI3 nanoplatelet shows its RMS roughness is ∼0.7  nm. (f) Laser output intensity as a function of pump intensity. (g) Evolution of emission spectra obtained at different pump intensities. (h) Lorentz fitting of a lasing oscillation mode at ≈781.3  nm gives an FWHM of 0.10 nm, corresponding to a Q factor of 7813. (i) Time-resolved photoluminescence (TRPL) spectra of perovskite nanoplatelet operating at spontaneous emission (P=11.12  μJ/cm2) and laser emission condition (P=24.8  μJ/cm2).

Fig. 3. (a) Microscopic images of a PbI2 passivated MAPbI3 nanoplatelet laser by operating at a pump intensity of 1.1Pth (16.48  μJ/cm2) for different times. (b) Microscopic image of MAPbI3 nanoplatelet after operating at 1.1Pth for 5600 s. (c) Lasing stability data of PbI2 passivated MAPbI3 nanoplatelet under femtosecond laser pumping with a repetition rate of 6 kHz in ambient air condition.

Fig. 4. (a) Schematic diagram of passivating the surface of MAPbI3 nanoplatelet with DBP (C64H36). (b) Process illustration of spin-coating a DBP film on the PbI2 passivated MAPbI3 nanoplatelet. (c) Laser output intensity as a function of pump intensity. (d) Evolution of emission spectra obtained at different pump intensities. (e) Lorentz fitting of a lasing oscillation mode at ≈779.9  nm, which gives an FWHM of 0.10 nm, corresponding to a Q factor of 7799. (f) Lasing stability data of the dual passivation processed MAPbI3 nanoplatelet laser under the femtosecond laser pumping with a repetition rate of 6 kHz in ambient air condition. Dual passivation refers to PbI2 passivation and DBP passivation.

Fig. 5. (a) Laser output intensity as a function of pump intensity. (b) Evolution of emission spectra obtained at different pump intensities. (c) TRPL spectra of a perovskite nanoplatelet without passivation operating at spontaneous emission (P=17.87  μJ/cm2) and laser emission condition (P=26.81  μJ/cm2).

Fig. 6. Lasing stability data of two other unpassivated MAPbI3 lasers under femtosecond laser pumping with a repetition rate of 6 kHz in ambient air condition.

Fig. 7. Emission spectra of an unpassivated MAPbI3 nanoplatelet laser after operating for different times measured using the ideaoptics PG2000 spectrometer (see Appendix A for more information).

Fig. 8. (a) AFM image of the edge of the unpassivated MAPbI3 nanoplatelet and (b) the corresponding cross view showing the thickness.

Fig. 9. XRD patterns of MAPbI3 nanoplatelets on mica substrate before and after exposure to the pump laser for 1800 s.

Fig. 10. Schematic diagram of the light path in an MAPbI3 nanoplatelet.

Fig. 11. (a) Schematic diagram of an MAPbI3 nanoplatelet on mica substrate being heated by a pump laser. (b) Transient thermal response of an MAPbI3 nanoplatelet. (c) Temperature of an MAPbI3 nanoplatelet at 290 fs after being pumped by a 290 fs laser pulse. (d) Radial temperature distribution of an MAPbI3 nanoplatelet at 290 fs after being pumped by a 290 fs laser pulse.

Fig. 12. (a) AFM image of the edge of PbI2 passivated MAPbI3 nanoplatelet and (b) the corresponding thickness.

Fig. 13. Lasing stability data of another two PbI2 passivated MAPbI3 lasers under femtosecond laser pumping with a repetition rate of 6 kHz in ambient air condition.

Fig. 14. (a) Image of the PbI2 passivated MAPbI3 nanoplatelets encapsulated with a DBP film on mica substrate and (b) image of unpassivated MAPbI3 nanoplatelets on mica substrate.

Fig. 15. Emission spectra of an unpassivated MAPbI3 nanoplatelet laser and a DBP passivated MAPbI3 nanoplatelet laser at the same pump intensity.

Fig. 16. Microscopic images of an MAPbI3 nanoplatelet after leaving in ambient air condition for (a) 0 h and (b) 48 h, respectively.

Fig. 17. Microscopic images of the PbI2 passivated MAPbI3 nanoplatelets encapsulated with a DBP film after leaving in ambient air condition for different times.

Fig. 18. Lasing stability data of another two dual passivation processed MAPbI3 lasers under femtosecond laser pumping with a repetition rate of 6 kHz in ambient air condition.

Fig. 19. Average operation time of unpassivated (sample A), PbI2 passivated (sample B), and dual passivation processed nanoplatelet lasers (sample C) under femtosecond laser pumping with a repetition rate of 6 kHz in ambient air condition.