Recent advances in the synthesis and passivation of pure bromide-based perovskite nanoplatelets

The peculiar properties of low-dimensional inorganic lead halide perovskite materials have triggered the attention of researchers in the past decade. The astonishing optoelectronic properties of these materials make them attractive for the next-generation light-emitting diodes. Perovskite nanoplatelets (NPLs) offer the advantage of thickness-controlled bandgap tunability, making them suitable for optoelectronic applications. However, the quantum efficiency of perovskite NPLs in thin films is substantially low compared with dispersions, due to their high surface-to-volume ratio. The undercoordinated atoms on the surface of the NPLs lead to the formation of a high density of defects, which consequently reduces the photoluminescence efficiency. In this review, we summarize various synthesis techniques and examine how the different ligand ratios affect the size, shape and morphological properties of the NPLs. We also investigate the effect of various isovalent and heterovalent ions in the A-site and B-site cations on the structural and optical properties. Furthermore, we have explored how metal ions influence the transformation of the morphological and optical properties of the nanocrystals into NPLs. The labile ligands on the surface can be easily detached during the purification process or as the material ages due to poor interaction between them. The loss of these ligands from the nanocrystal surface leads to the formation of defects. This leads to the formation of deep traps within the bandgap and consequently reduces quantum efficiency. In this review, we discuss various ligands used for passivation of the surface defects through in situ and post-synthesis methods. During the in situ passivation process, we focus on the role played by multidentate ligands, sulphur, phosphorus, polymer, zwitterionic compounds, silanes, and short-chain ligands. These ligands have demonstrated efficacy as passivating agents, helping to maintain high quantum efficiency and long-term stability. In the post-synthesis passivation strategy, several ligands are evaluated including metal bromide-ligand solution, polysalt, bidentate ligands and short-chain ligands. The ligands enhance the stability while introducing new properties based on their functional moieties. Additionally, we rationalize the effects of different chiral ligands and their surface chemistry related to the synthesis and passivation of the NPLs.