Understanding the Effect of Acid-Base Equilibria in Ligand Exchange on the Overall Quality of Inorganic Perovskite Nanocrystals and Light-Emitting Devices

Photoluminescence quantum yield (PLQY) losses in inorganic perovskite nanocrystals (PeNCs) due to ligand desorption hamper high external quantum efficiencies (EQE) in corresponding perovskite light-emitting devices (PeLEDs). Their low PLQYs derive mainly from ligand desorption during device fabrication. Post-synthesis treatments contribute to inefficiently adsorbed ligands due to their unfavorable chemical environments. Here the acid/base dynamics of treatments are investigated by applying a chemoselective and aprotic-driven ligand exchange strategy that favors neutral environments, in lieu of traditional acid-mediated strategies. Mild ligand-extracting reagents (LERs) are utilized to gently extract native anchoring ligands with their cations, while their anions temporarily passivate the PeNC's surface, ensuring steady colloidal stability. By applying tri-ethyloxonium tetrafluoroborate (TET) as the LER, PeNCs films displayed PLQYs as high as 92.8%. When paired with the widely-employed di-dodecyldimethylammonium bromide (DDAB) ligand, PeLED devices based on TET-treated PeNCs exhibited a maximum EQE of 22.94% for emissions at λ = 512 nm. The work highlights the versatility of ligand exchange processes by assessing their overall governing factors.