Fig. 1. Schematic diagrams of i-BA⁺, BA⁺ and PEA⁺ organic cations and dual source vapor deposition

Fig. 2. Quasi-2D perovskite templates with different organic spacers (a) UV-Vis spectra; (b) XRD patterns

Fig. 3. Crystal structures of the films. (a) XRD pattern; (b) (110) peak intensity and FWHM

Fig. 4. control, @i-BAI, @BAI and @PEAI film morphologies. (a)‒(d) Surface SEM; (e)‒(h) cross-sectional SEM; (i)‒(l) the particle size statistics of the corresponding films, respectively

Fig. 5. Photoelectric properties of MAPbI₃ thin film. (a) UV-Vis spectra; (b) PL spectra; (c) TRPL spectra

Fig. 6. Evaporation process parameters. (a) Evaporation temperature; (b) evaporation rate and chamber pressure

Fig. 7. Template induced growth process. (a) Optical photographs of the films with different thicknesses; (b) quasi-2D perovskite surface morphology; (c) Gibbs free energy versus particle radius; (d) morphological evolution of control films; (e) morphological evolution of @i-BAI films

Fig. 8. MAPbI₃ thin film XPS spectra. (a) Pb4f; (b) I3d; (c) N1s; (d) I∶N∶Pb element ratio

Fig. 9. Band gap and UPS tests of thin films. (a) tauc plot; (b) cut-off Region; (c) VB edge region; (d) schematic diagram of the energy band structure

Fig. 10. quasi-2D/3D perovskite solar cell performance. (a) J-V curve; (b) EQE; (c) short-circuit current distribution; (d) PCE distribution