Fig. 1. Schematic of experimental device for two-step vapor deposition method. (a) Schematic of the device for synthesis of SnI₂ nanoplatelets. (b) schematic of the device for synthesis of CH₃NH₃SnI₃ nanoplatelets

Fig. 2. Optical microscopy images of SnI₂ precursors grown on mica substrates under different experimental conditions. Optical micrographs of SnI₂ precursors grown at H₂ gas flow rates of (a) 14 mL/min, (b) 16 mL/min, and (c) 18 mL/min; optical micrographs of SnI₂ precursors grown at deposition time of (d) 20 min, (e) 30 min, and (f) 35 min

Fig. 3. Optical properties of controllable content nanoplatelets. (a) XRD diagrams and (b) absorption spectra of CH₃NH₃SnI₃ nanoplatelet grown under different Ar flow rates; (c) XRD diagrams and (d) absorption spectra of CH₃NH₃SnI₃ nanoplatelet with reaction time of 150, 160, and 170 min

Fig. 4. Relevant characterization of CH₃NH₃SnI₃ nanoplatelet under 40 mL/min and 160 min conditions. (a) Absorption spectrum, the illustration shows the band gap corresponding to the absorption spectrum; (b) PL spectra at different pump powers

Fig. 5. Optical microscopy, XRD, and cross-sectional images of nanoplatelet before and after spin coating of PMMA thin film. (a) Optical microscopy of uncoated PMMA film (above image) and microscopy of the nanoplatelet passivated by PMMA film (below image); (b) XRD images of newly converted CH₃NH₃SnI₃ nanoplatelet and spin coated PMMA thin films at N₂ atmosphere for 48 h; (c) cross-section of the edges of SnI₂ and CH₃NH₃SnI₃ nanoplatelets after spin coating PMMA film (illustrations are optical micrographs of SnI₂ and CH₃NH₃SnI₃ nanoplatelets respectively)