Crystallization control based on A-site cation strategy for blue FAPbBr3 perovskite nanoplatelets with pure emission

Two-dimensional (2D) lead halide perovskite with attractive properties is considered one of the most promising candidates for preparing blue-emitting materials and corresponding optoelectronic devices. For the formamidinium-based (FA) nanoplatelets (NPLs), despite exhibiting better optical performance compared to their counterparts, it is still challenging to precisely control their emission in the blue region during synthesis and the influence of chloroform on the components of FAPbBr3 have not been investigated thoroughly. Herein, it is revealed that the decomposition of chloroform during the synthesis will introduce Cl into the crystal with the assistance of surface ligands, leading to the mixed-halide perovskite. Further, an A-site cation strategy was introduced for tuning the spectra of FAPbBr3 NPLs. The addition of Cs with a small ionic radius can shrink the arrangement of octahedrons and enhance their interactions, which will promote the seeding growth of perovskite and form uniform crystals. With help of surface ligands, these uniform crystals will further grow to form ho-mogeneous perovskite NPLs. The obtained NPLs show the pure emission from sky-blue to deep-blue. To the best of our knowledge, it is the first report about finely tuning the emission of FAPbBr3 in the blue region. This crystallization control strategy by introducing Cs is beneficial for their further applications in the field of pho-toelectric devices.