(Invited) A “Cocktail” Approach to Effective Passivation of Metal Halide Perovskite Magic Sized Clusters and Quantum Dots Using Novel Planar Molecular Ligands Based on Trivalent Metal Nitrate Coordination Complex

Abstract

Metal halide perovskites nanoparticles, including magic sized clusters (MSCs) and perovskite quantum dots (PQDs), exhibit interesting properties promising for emerging applications in energy and photonics. Their stabilization is critical for maintaining their properties and functionalities. One approach to stabilization is to use molecular ligands to passivate their surface. We have discovered a new class of molecular ligands based on trivalent metal nitrate coordination complex that is highly effective in passivating perovskite MSCs or PQDs. We can tune from PQDs to MSCs at will by adjusting the ligand concentration and/or using different ligands, with stronger binding ligands and higher ligand concentration favoring MSCs over PQDs. Both the MSCs and PQDs are highly stable and photoluminescent. Experimental evidence suggests that the planar geometry of the coordination ligands is critical for the outcomes observed. Such ligands should work for both nanoparticles and bulk films, and are likely more desired than linear or “cone-shaped” ligands. The results indicate that the size, shape, charge (including distribution), orientation, and inter-ligand interaction are critical characters affecting the effectiveness of passivation. Furthermore, due to the nature of multiple defects on the MSC or PQD surface, a combination of ligands is required for effective passivation, essentially a “cocktail” approach. We also found that the approach works well for both all inorganic perovskites such as CsPbBr3 as well as organo-metal halide perovskites such as CH3NH3PbBr3. We suggest that the passivation approach developed may be applicable to materials beyond perovskites.