CsPbCl3 → CsPbI3 Exchange in Perovskite Nanocrystals Proceeds through a Jump-the-Gap Reaction Mechanism

Halide Exchange in Perovskites Enables Bromine/Iodine Hybrid Cathodes for Highly Durable Zinc Ion Batteries

With the increasing need for reliable storage systems, the conversion-type chemistry typified by bromine cathodes attracts considerable attention due to sizeable theoretical capacity, cost efficiency, and high redox potential. However, the severe loss of active species during operation remains a problem, leading researchers to resort to concentrated halide-containing electrolytes. Here, profiting from the intrinsic halide exchange in perovskite lattices, a novel low-dimensional halide hybrid perovskite cathode, TmdpPb2[IBr]6, which serves not only as a halogen reservoir for reversible three-electron conversions but also as an effective halogen absorbent by surface Pb dangling bonds, C─H…Br hydrogen bonds, and Pb─I…Br halogen bonds, is proposed. As such, the Zn||TmdpPb2[IBr]6 battery delivers three remarkable discharge voltage plateaus at 1.21 V (I0/I-), 1.47 V (I+/I0), and 1.74 V (Br0/Br-) in a typical halide-free electrolyte; meanwhile, realizing a high capacity of over 336 mAh g-1 at 0.4 A g-1 and high capacity retentions of 88% and 92% after 1000 cycles at 1.2 A g-1 and 4000 cycles at 3.2 A g-1, respectively, accompanied by a high coulombic efficiency of ≈99%. The work highlights the promising conversion-type cathodes based on metal-halide perovskite materials.

Structural and optical control through anion and cation exchange processes for Sn-halide perovskite nanostructures

Metal halide perovskite nanostructures, characterized by their ionic nature, present a compelling avenue for the tunability of dimensions and band gaps through facile compositional transformations involving both cationic and anionic exchange reactions. While post-synthetic ion-exchange processes have been extensively explored in Pb-halide perovskite nanocrystals, the inherent instability of Sn2+ has limited the exploration of such processes in Sn-halide perovskite nanostructures. In this study, we present a straightforward cation exchange process wherein 2D [R-NH3]2SnX4 Ruddlesden-Popper (RP) nanostructures with n = 1 transition to 3D ASnX3 nanocrystals at room temperature with the addition of A-cation oleate. In addition, anion exchange processes have been demonstrated for both 2D [R-NH3]2SnX4 RP nanostructures and 3D nanocrystals, showcasing transitions between iodide and bromide counterparts. Furthermore, we have fabricated a thin film of 2D [R-NH3]2SnX4 RP nanostructures for cation exchange, wherein A-cation diffusion through a liquid-solid interface facilitates the transformation into a 3D ASnX3 crystal. This investigation underscores the versatility of ion exchange processes in engineering the composition of Sn-halide perovskite nanostructures and, consequently, modulating their optical properties.

Fast Organic Cation Exchange in Colloidal Perovskite Quantum Dots toward Functional Optoelectronic Applications

Colloidal quantum dots with lower surface ligand density are desired for preparing the active layer for photovoltaic, lighting, and other potential optoelectronic applications. In emerging perovskite quantum dots (PQDs), the diffusion of cations is thought to have a high energy barrier, relative to that of halide anions. Herein, we investigate the fast cross cation exchange approach in colloidal lead triiodide PQDs containing methylammonium (MA+) and formamidinium (FA+) organic cations, which exhibits a significantly lower exchange barrier than inorganic cesium (Cs+)-FA+ and Cs+-MA+ systems. First-principles calculations further suggest that the fast internal cation diffusion arises due to a lowering in structural distortions and the consequent decline in attractive cation-cation and cation-anion interactions in the presence of organic cation vacancies in mixed MA+-FA+ PQDs. Combining both experimental and theoretical evidence, we propose a vacancy-assisted exchange model to understand the impact of structural features and intermolecular interaction in PQDs with fewer surface ligands. Finally, for a realistic outcome, the as-prepared mixed-cation PQDs display better photostability and can be directly applied for one-step coated photovoltaic and photodetector devices, achieving a high photovoltaic efficiency of 15.05% using MA0.5FA0.5PbI3 PQDs and more precisely tunable detective spectral response from visible to near-infrared regions.

Epitaxial Heterostructures of CsPbBr3 Perovskite Nanocrystals with Post-transition Metal Bismuth

The facet chemistry of halide perovskite nanocrystals plays a key role in designing nanoscale epitaxial heterostructures. However, despite significant successes achieved in designing these nanocrystals, their heterostructures with several leading transition metals could not be established yet. Herein, the possible heterostructures of metals beyond transition metals are explored and the epitaxial combinations of soft CsPbBr3 nanocrystals with the post-transition metal Bi(0) are reported. These heterostructures are built with interfacing facets having hexagonal atomic configurations of both the rhombicuboctahedron CsPbBr3 and octahedral Bi(0). A high reaction temperature and the presence of alkylamine kept Bi(III) in reduced form and helped in sustaining these CsPbBr3-Bi(0) heteronanocrystals. Since understanding of and synthesis optimization of metal-halide perovskite heterostructures are limited, this finding adds a new fundamental insight in designing ionic and nonionic materials heterojunctions. Furthermore, oxidation and sulfidation of Bi(0) are studied, and the possible oxide/sulfide heterostructures with CsPbBr3 are discussed.