Lead halide perovskite nanocrystals (LHP NCs) are a state-of-the-art light-harvesting material, prized for their outstanding optoelectronic properties—high absorption coefficient, extensive charge carrier diffusion lengths, and low exciton binding energy. Despite achieving remarkable photovoltaic performance with a photoconversion efficiency exceeding 25% within a decade, the transition of LHP to industrial-scale development encounters obstacles due to moisture intolerance and ambient instability [1].

The inorganic/hybrid core of LHP NCs contributes to their unique photophysical properties, while surface ligands play a crucial role in stabilizing and influencing charge transfer dynamics in diverse environments [2,3]. Therefore, understanding the complex NC-ligand interfacial chemistry is vital for achieving colloidal stability in aqueous and polar media.

Our solution involves optimizing hydrophilic and hydrophobic interactions on the LHP NC surface using engineered multidentate ligands. We developed NKE-12, a bolaamphiphilic ligand derived from lysine (K) and glutamic acid (E), featuring multiple cationic (NH₃⁺) and anionic (COO^-) anchoring groups. Applied in a ligand exchange treatment on CsPbBr₃ NCs, NKE-12 achieved effective surface passivation and water molecule localization away from the inorganic core through hydrophilic interactions [4]. Confirmation of successful ligand exchange was obtained through Fourier transform infrared and X-ray photoelectron spectroscopy. Structural integrity was preserved and validated by transmission electron microscopy and X-ray diffraction patterns. NKE-12 binding interactions on the NC surface were elucidated through multidimensional nuclear magnetic resonance ligand spectroscopy [5].

Deconstructing NKE-12 into NK-12 and NE-12 fragments provided insights into the individual roles of cationic and anionic terminal ends in passivation and solvent phase transfer. The synergistic effect of robust ligand binding and increased hydrophilicity resulted in significant two-week-long water stability for CsPbBr₃/NKE-12 NCs compared to oleylamine/oleic acid capped NCs. Enhanced charge separation and transport capabilities observed through electrochemical measurements prompted the exploration of photocatalytic attributes. Water-stabilized CsPbBr₃/NKE-12 NCs exhibited excellent photocatalytic activity for acrylamide polymerization, showcasing their potential for diverse applications.

Presently, we are expanding ligand engineering, exploring different multi-ionic ligands to further extend water stability and deepen our understanding of photogenerated charge extraction processes. Our findings on ligand design principles for developing moisture-resistant perovskite NCs hold significant promise for applications in photovoltaics and photocatalysis.