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

Abstract 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.