Colloidal synthesis of lead-free all-inorganic cesium bismuth bromide perovskite nanoplatelets

Lead halide two-dimensional (2D) nanoplatelets (NPLs) have attracted intense interest due to their unique optoelectronic properties. However, environmental friendly lead-free 2D perovskite NPLs are highly desirable in terms of application. Herein, all-inorganic Cs 3 Bi 2 Br 9 perovskite NPLs are synthesized for the first time via the hot injection method. The Cs 3 Bi 2 Br 9 NPLs are parallelogram-shaped and exhibit an extremely sharp first exciton peak which blue-shifts substantially with respect to their bulk bandgap. The formation of Cs 3 Bi 2 Br 9 NPLs is determined by the layered feature of Cs 3 Bi 2 Br 9 crystalline structure and the shape of parallelogram is the reflection of the trigonal nature of Cs 3 Bi 2 Br 9 crystal. The large blue-shift and extremely sharp first exciton peak are due to large exciton binding energy and quantum confinement in the Cs 3 Bi 2 Br 9 NPLs and large exciton binding energy in Cs 3 Bi 2 Br 9 crystal. The Cs 3 Bi 2 Br 9 NPLs grow anisotropically from monodispersed parallelogram-shaped nuclei via Ostwald ripening, demonstrated by ex situ TEM investigation. Anion-exchange was used to effectively adjust the composition of the Cs 3 Bi 2 Br 9 NPLs. Additionally, the Cs 3 Bi 2 Br 9 NPLs exhibit excellent stability to air and illumination due to the robust crystal, BiOBr passivation and oleylamine and oleic acid co-passivation.