Studies of high-membered two-dimensional Ruddlesden-Popper Cs 7 Pb 6 I 19 perovskite nanosheets via kinetically controlled reactions.

Two-dimensional (2D) all-inorganic Ruddlesden-Popper (RP) perovskite Cs 7 Pb 6 I 19 nanosheets (NSs) were successfully developed for the first time by employing a structural recrystallization process with additional passivation of small organic sulfide molecules. The structure of Cs 7 Pb 6 I 19 NSs is confirmed by powder X-ray diffraction measurements, atomically-resolved STEM measurements and atomic force microscopy (AFM) studies. Cs 7 Pb 6 I 19 NSs with a specific n value of 6 exhibits unique absorption and emission spectra with intense excitons at 560 nm due to quantum confinement effects in 2D perovskite slabs. The formation mechanisms of 2D Cs 7 Pb 6 I 19 NSs and 3D γ-CsPbI 3 phases were investigated by in situ photoluminescence (PL) spectroscopy and the activation energies of their formation reactions were calculated to be 151 kJ mol -1 and 95.3 kJ mol -1 , respectively. The phase stability of 2D Cs 7 Pb 6 I 19 NSs can be maintained at temperatures below 14 °C for more than 4 weeks. The overall results indicate that 2D Cs 7 Pb 6 I 19 NSs demonstrate unique optical properties and structural stability compared with other 3D perovskite materials. We have opened a new path to the future discovery of 2D perovskite structures with metastable phases by using this recrystallization method and the assistance of sulfur-derived organic molecules.