Tuning the orientation of self-assembled CsPbBr3 perovskite nanoplatelet superlattices through ligand engineering

Controlling the orientation of perovskite nanoplatelets (NPLs) is critical to realize their benefits in improving outcoupling and achieving polarized light emission. Herein, we report an approach to finely tune the orientation of CsPbBr 3 perovskite NPL superlattices by partially substituting native ligands with organo-ammonium bromide ligands, enabling systematic modulation of NPL orientation from face down to edge up. Using a long-chain organic backbone (oleylammonium) favors the edge-up orientation, leading to a higher degree of linear polarization. Through in situ photoluminescence measurements, we show that these long-chain organo-ammonium bromide ligands sterically hinder growth, resulting in smaller NPLs that are easier to orient edge up. On the other hand, with shorter-chain ligands (butylammonium), NPLs are larger with weaker inter-ligand interactions, favoring a face-down orientation that improves outcoupling and the efficiency of blue NPL light-emitting diodes. The principles for orientation control demonstrated here are generalizable and allow the multifunctionality of anisotropic nanocrystals to be harnessed.