Optical Property and Stability of Lead‐Free Cs3Sb2Br9 Perovskite Microplatelets Prepared by a Solution Method

Herein, a solution method is used to synthesize lead‐free Cs 3 Sb 2 Br 9 perovskite microplatelets. The freshly prepared microplatelets exhibit photoluminescence (PL) peaks at about 420 and 600 nm, when the excitation wavelengths are 325 and 532 nm, respectively. The 420 nm PL band is attributed to the band edge excitonic recombination while the 600 nm PL band originates from radiative defect state. The 600 nm emission is stronger than that of the 420 nm emission, implying the high density of defects and relatively poor crystal quality. Moreover, 2D PL and Raman mappings indicate the presence of defects at the edges. These features suggest the crystal quality, so as the structural stability of the Cs 3 Sb 2 Br 9 microplatelets obtained by solution method is relatively inferior. During the storage, the Cs 3 Sb 2 Br 9 microplatelets significantly degrade and the PL rapidly quenches. To improve the stability, a surface capping strategy by oleic acid (OA) is developed. The PL intensity retains more than 80% and the morphology maintains after storage for about one month, demonstrating the improved stability of the OA‐capped Cs 3 Sb 2 Br 9 microplatelets.