Ligands Mediate Anion Exchange between Colloidal Lead-Halide Perovskite Nanocrystals

Abstract

The soft lattice of lead-halide perovskite nanocrystals (NCs) allows tuning their optoelectronic characteristics via anion exchange by introducing halide salts to a solution of perovskite NCs. Similarly, cross-anion exchange can occur upon mixing NCs of different perovskite halides. This process, though, is detrimental for applications requiring perovskite NCs with different halides in close proximity. We study the effects of various stabilizing surface ligands on the kinetics of the cross-anion exchange reaction, comparing zwitterionic and ionic ligands. The kinetic analysis, inspired by the "cage effect" for solution reactions, showcases a mechanism where the surface capping ligands act as anion carriers that diffuse to the NC surface, forming an encounter pair enclosed by the surrounding ligands that initiates the anion exchange process. The zwitterionic ligands considerably slow down the cross-anion exchange process, and while they do not fully inhibit it, they confer improved stability alongside enhanced solubility relevant for various applications.

Universal scaling laws for charge-carrier interactions with quantum confinement in lead-halide perovskites

“…Synthesis of CsPb(Cl x Br 1-x ) 3 NCs with x~0.3 CsPb(Br/Cl) 3 NCs with size ~30 nm were prepared by partial anionexchange of CsPbBr 3 NCs 57,58 .…”

Facets-Directed Epitaxially Grown Lead Halide Perovskite-Sulfobromide Nanocrystal Heterostructures and Their Improved Photocatalytic Activity

“…Lead halide perovskite nanocrystal heterostructures remain one of the most aspirant optical materials in current research because of the possibility of enhancing their charge carrier transportation in devices and also imparting phase and/or optical stability compared to the parent perovskite nanocrystals. − In spite of extensive research in developing bright and color tunable emissions from different halide perovskite nanocrystals, − the heterostructures of any of their combinations are limited. While shapes have been tuned, sizes can be varied, growths have been controlled, phase and optical stability have been understood, and surface-ligand chemistry has also been investigated, − the hetero-epitaxial growth of other material or even same halide perovskite nanocrystals on preformed or parent perovskite nanocrystals could not be successfully achieved yet. Even a second-layer growth or shelling of another or the same material on seed nanocrystals also could not be carried out in spite of the large successes achieved in understanding the chemistry of formation of these nanocrystals. , Most of such reports on all-inorganic heterostructures involve non-epitaxial or random deposition of secondary materials without giving a proper chemistry of the growth of one on the surface of another material. − ,− Hence, designing epitaxial heterostructures of lead halide perovskites remained timely important to boost their charge carrier transport activity and also shelling with different materials to induce long-term ambient stability.…”

Improving anion-exchange efficiency and spectrum stability of perovskite quantum dots via an Al3+ bonding-doping synergistic effect

“…A typical solution is the ligand-assisted strategy, which provides a halogen source and can effectively decrease the superficial defects of QDs during the post-synthesis process. 23,24…”

“…A typical solution is the ligand-assisted strategy, which provides a halogen source and can effectively decrease the superficial defects of QDs during the post-synthesis process. 23,24 The shortcomings discussed above are unfavorable for the preparation of high-quality QDs. Therefore, most research still focuses on reducing the anion exchange-induced instability of perovskite QDs, especially the spectral shift and performance degradation of QDs and LEDs.…”