Passivation of Perovskite Nanocrystals Using Trifunctional Peptide Molecular Ligands

The strategy of using bifunctional peptides as passivating ligands in the assembly of perovskite nanocrystals (PNCs) has emerged recently. Bifunctional peptides contain amino (-NH₂) and carboxylic groups (-COOH) can target cationic and anionic defect sites of PNC surfaces. They are highly favorable in the synthesis of methyl ammonium lead bromide (CH₃NH₃PbBr₃) PNCs. Although the PL enhancement on bifunctional peptides has been investigated in some studies, there are only a few reports on the effects trifunctional peptides have on PNCs. Further research is required to optimize the PL properties of PNCs using trifunctional peptides as passivating ligands. We hypothesize that trifunctional peptides will passivate surface defects of PNCs as well. L-cysteine, a trifunctional amino acid containing three functional groups, amino, carboxylic, and sulfhydryl (-SH) groups was used as a capping ligand. L-cystine with different lengths and concentration was used in the precursor solution with PNCs. Synergistic effects of the three functional groups led to strong binding interactions between L-cysteine and PNCs. Therefore, L-cysteine ligands passivated the surface defect sites of PNCs effectively, and facilitated the self-assembly process to form stable nanocrystals. The stability of PNCs was tested by observing the X-ray Diffraction (XRD) patterns, and obtaining the UV-vis and PL spectra. These PNCs showed strong PL and stable optical properties. Using trifunctional peptide, L-cysteine, as capping ligands, CH₃NH₃PbBr₃ PNCs was synthesized successfully. This study shows that using trifunctional peptide molecular ligands in the assembly of PNCs is a promising method.