Surface- vs Diffusion-Limited Mechanisms of Anion Exchange in CsPbBr₃ Nanocrystal Cubes Revealed through Kinetic Studies

Abstract

Ion-exchange transformations allow access to nanocrystalline materials with compositions that are inaccessible via direct synthetic routes. However, additional mechanistic insight into the processes that govern these reactions is needed. We present evidence for the presence of two distinct mechanisms of exchange during anion exchange in CsPbX3 nanocrystals (NCs), ranging in size from 6.5 to 11.5 nm, for transformations from CsPbBr3 to CsPbCl3 or CsPbI3. These NCs exhibit bright luminescence throughout the exchange, allowing their optical properties to be observed in real time, in situ. The iodine exchange presents surface-reaction-limited exchanges allowing all anionic sites within the NC to appear chemically identical, whereas the chlorine exchange presents diffusion-limited exchanges proceeding through a more complicated exchange mechanism. Our results represent the first steps toward developing a microkinetic description of the anion exchange, with implications not only for understanding the lead halide perovskites but also for nanoscale ion exchange in general.

Highly Luminescent CsPbX3 (X=Cl, Br, I) Nanocrystals Achieved by a Rapid Anion Exchange at Room Temperature

“…Then, we employ kinetic equations to further verify the effect of the above two factors . The completed derivation process can be found in the Supporting information.…”

Fully‐Inorganic Trihalide Perovskite Nanocrystals: A New Research Frontier of Optoelectronic Materials

“…[35][36][37]68,105,[121][122][123] The used halide sources include organic (methylammonium halide, tetrabutylammonium halide, tetraoctylammonium halide, and octadecylammonium halide, etc.) [124] It was found that the halide exchange mechanisms of transformation from CsPbBr 3 to CsPbI 3 is obviously different from that of transformation from CsPbBr 3 to CsPbCl 3 . [36,37,78,105,[121][122][123] The possible mechanisms of halide exchange transformation in CsPbX 3 cube NCs (the edge length ranging from 6.5 to 11.5 nm) from CsPbBr 3 to CsPbI 3 or CsPbCl 3 have been explored.…”

“…[36,37,78,105,[121][122][123] The possible mechanisms of halide exchange transformation in CsPbX 3 cube NCs (the edge length ranging from 6.5 to 11.5 nm) from CsPbBr 3 to CsPbI 3 or CsPbCl 3 have been explored. [124] It was found that the halide exchange mechanisms of transformation from CsPbBr 3 to CsPbI 3 is obviously different from that of transformation from CsPbBr 3 to CsPbCl 3 . The former presents surface-reaction-limited exchanges allowing all anionic sites within the NCs to appear chemically identical, whereas the latter is likely diffusion-limited, producing zones of exchange.…”

“…[124] In addition to taking place in solution medium, a solid-state anion exchange for CsPbX 3 NCs could be realized within minutes to hours only by embedding pure and dry perovskite NCs into various ionic salt matrices (KBr, KCl, and KI) at RT. [124] In addition to taking place in solution medium, a solid-state anion exchange for CsPbX 3 NCs could be realized within minutes to hours only by embedding pure and dry perovskite NCs into various ionic salt matrices (KBr, KCl, and KI) at RT.…”

All‐Inorganic Halide Perovskites for Optoelectronics: Progress and Prospects

“…On the one hand, changing the halide compositions of nanocrystals is an effective method to obtain IMH perovskites with different bandgaps and optical absorptions . To achieve this goal, several studies have reported the synthesis of different colloidal CsPbX 3 nanocrystals by adding different or mixed PbX 2 salts in the process of the reaction .…”