Improving the Stability of Colloidal CsPbBr<sub>3</sub> Nanocrystals with an Alkylphosphonium Bromide as Surface Ligand Pair
Meenakshi Pegu, Hossein Roshan, Clara Otero‐Martínez, Luca Goldoni, Juliette Zito, Nikolaos Livakas, Pascal Rusch, Francesco De Boni, Francesco Di Stasio, Ivan Infante, Luca De Trizio, Liberato Manna
Abstract
High Resolution Image Download MS PowerPoint Slide In this study, we synthesized a phosphonium-based ligand, trimethyl(tetradecyl)phosphonium bromide (TTP-Br), and employed it in the postsynthesis surface treatment of Cs-oleate-capped CsPbBr 3 nanocrystals (NCs). The photoluminescence quantum yield (PLQY) of the NCs increased from ∼60% to more than 90% as a consequence of replacing Cs-oleate with TTP-Br ligand pairs. Density functional theory calculations revealed that TTP + ions bind to the NC surface by occupying Cs + surface sites and orienting one of their P–CH 3 bonds perpendicular to the surface, akin to quaternary ammonium passivation. Importantly, TTP-Br-capped NCs exhibited higher stability in air compared to didodecyldimethylammonium bromide-capped CsPbBr 3 NCs (which are considered a benchmark system), retaining ∼90% of their PLQY after 6 weeks of air exposure. Light-emitting diodes fabricated with TTP-Br-capped NCs achieved a maximum external quantum efficiency of 17.2%, demonstrating the potential of phosphonium-based molecules as surface ligands for CsPbBr 3 NCs in optoelectronic applications.