From Heterostructures to Solid‐Solutions: Structural Tunability in Mixed Halide Perovskites

Abstract

The stability, reliability, and performance of halide‐perovskite‐based devices depend upon the structure, composition, and particle size of the device‐enabling materials. Indeed, the degree of ion mixing in multicomponent perovskite crystals, although challenging to control, is a key factor in determining properties. Herein, an emerging method termed evaporation–crystallization polymer pen lithography is used to synthesize and systematically study the degree of ionic mixing of Cs0.5FA0.5PbX3 (FA = formamidinium; X = halide anion, ABX3) crystals, as a function of size, temperature, and composition. These experiments have led to the discovery of a heterostructure morphology where the A‐site cations, Cs and FA, are segregated into the core and edge layers, respectively. Simulation and experimental results indicate that the heterostructures form as a consequence of a combination of both differences in solubility of the two ions in solution and the enthalpic preference for Cs–FA ion segregation. This preference for segregation can be overcome to form a solid‐solution by decreasing crystal size (<60 nm) or increasing temperature. Finally, these tools are utilized to identify and synthesize solid‐solution nanocrystals of Cs0.5FA0.5Pb(Br/I)3 that significantly suppress photoinduced anion migration compared to their bulk counterparts, offering a route to deliberately designed photostable optoelectronic materials.

Strain Regulation and Photophysical Properties in Halide Perovskite

“…Phase segregation in halide perovskite presents a major challenge for achieving high efficiency and stability in devices, as it is often caused by ion migration driven by the strain of the perovskite lattice. [ 61–63 ] Ehrler and co‐workers observed a reduction in the formation rates of both I‐ and Br‐rich phases in MAPb(Br x I 1− x ) 3 by incorporating a smaller cation, which is mainly attributed to the increase in activation energy of ion migration, as shown in Figure 2d. [ 64 ] Subsequently, applying a physical pressure of 0.3 GPa was found to further restrain the phase segregation by compressing the perovskite lattice.…”

Ion Diffusion Dynamics and Halogen Mixing at the Heterojunction of Halide Perovskites: Atomistic Insights

“…However, a comprehensive atom-istic study exploring the interfacial ion dynamics and their correlation with various local structural and compositional factors is still largely missing. 57 Here, we computationally model the heterojunction between A-cation mixed perovskites FA 0.875 Cs 0.125 PbI 3 and FA 0.875 Cs 0.125 PbBr 3 with FA 0.875 Cs 0.125 PbBr 3 surrounded by FA 0.875 Cs 0.125 PbI 3 similar to the structures studied by Shin et al 63 These FA-Cs mixed perovskites exhibit enhanced lattice and phase stability and improved photophysical properties, prompting their wide usage as optoelectronic devices. 18−20 The inequivalent interfaces modeled along the two equatorial planes (100) and (010) exhibit different extents of intrinsic structural strain.…”

“…Here, we computationally model the heterojunction between A-cation mixed perovskites FA 0.875 Cs 0.125 PbI 3 and FA 0.875 Cs 0.125 PbBr 3 with FA 0.875 Cs 0.125 PbBr 3 surrounded by FA 0.875 Cs 0.125 PbI 3 similar to the structures studied by Shin et al These FA-Cs mixed perovskites exhibit enhanced lattice and phase stability and improved photophysical properties, prompting their wide usage as optoelectronic devices. − The inequivalent interfaces modeled along the two equatorial planes (100) and (010) exhibit different extents of intrinsic structural strain. The local strain relaxation further influences the energetics associated with the anion vacancy formation at these interfaces. , The detailed simulations of interfacial ion diffusion exhibit the directionally anisotropic characteristics of anion migration in these perovskite heterojunctions.…”

Discovering polyelemental nanostructures with redistributed plasmonic modes through combinatorial synthesis

“…To do this, we used scanning probe block copolymer lithography (SPBCL) to synthesize a particle library containing individually addressable heterojunction nanoparticles with various metal types, compositions, particle shapes, and domain configurations. SPBCL and these massively parallel printing tools have been used to synthesize polyelemental metallic (28)(29)(30), oxides/sulfides (31)(32)(33), and halide perovskite nanocrystals (34)(35)(36) configured as solid solutions and phase-separated structures, and, recently, new types of intermetallic metal nanostructures, including Au 3 Cu intermetallic nanoprisms formed by concurrent chemical ordering and stacking discontinuities (30), were found through correlative electron microscopy techniques. Building on this work, the current study explores thousands of locationindexed heterojunction nanoparticles on microscopy-compatible chips and then correlates the elemental distributions and geometries of individual nanoparticles with their electromagnetic responses in both near and far fields.…”