First-principles study of electronic properties of amine ligand-capped CsPbBr3 surface with organo-metallic alumina precursor treatment

Water and oxygen stability has been one of the major bottlenecks in practical application of perovskite quantum dots (PeQDs). Recently, ultra-thin alumina via atomic layer deposition (ALD) has been used as protective coating to improve the stability of PeQDs. However, the use of organo-metallic trimethylaluminum (TMA) precursor is typically accompanied by undesirable photoluminescence quenching of PeQDs. We investigate in detail the interaction mechanism between TMA and amine ligands-capped PeQDs to shed light on the origin of such quenching. First-principles calculations reveal that TMA is highly reactive to insert into amine ligands and PeQDs, which disrupts the bonding between ligand and the PeQDs surface. The demethylation of the insertion product would induce substantial trap states on the PeQDs surface, resulting in the degradation of photo-luminescence. Methyl aluminum diisopropoxide (MADI) with asymmetric structure is proposed as an ALD pre-cursor for the treatment of PeQDs. Due to the tight binding of the isopropyl groups to the Al atom, MADI can effectively avoid successive dissociation after reaction with surface ligands, avoiding the formation of trap states. This work highlights the importance of precursor engineering for ligand passivation and provides guidance to the design of precursors with minimal trap-states for highly efficient and stable PeQDs.