Anion‐Exchange Driven Phase Transition in CsPbI₃ Nanowires for Fabricating Epitaxial Perovskite Heterojunctions

Abstract

Anion‐exchange in halide perovskites provides a unique pathway of bandgap engineering for fabricating heterojunctions in low‐cost photovoltaics and optoelectronics. However, it remains challenging to achieve robust and sharp perovskite heterojunctions, due to the spontaneous anion interdiffusion across the heterojunction in 3D perovskites. Here, it is shown that the anionic behavior in 1D perovskites is fundamentally different, that the anion exchange can readily drive an indirect‐to‐direct bandgap phase transition in CsPbI3 nanowires (NWs) and greatly lower the phase transition temperature. In addition, the heterojunction created by phase transition is epitaxial in nature, and its chemical composition can be precisely controlled upon postannealing. Further study of the phase transition dynamics reveals a threshold‐dominating anion exchange mechanism in these 1D NWs rather than the gradient‐dominating mechanism in 3D systems. The results provide important insights into the ionic behavior in halide perovskites, which is beneficial for applications in solar cells, light‐emitting diodes (LEDs), and other semiconductor devices.

Halide Anion-Exchange-Driven Structural Phase Transition in CsPbX3 Perovskites: Alloys versus Heterostructures

“…Li et al utilized the solid−solid anion-exchange process to prepare epitaxial heterojunctions in yellow-phase Y-CsPbI 3 nanowires. 32 They found that the anion-exchange reactions drive the structural transition from Y-CsPbI 3 to black-phase CsPb(I x Br 1−x ) 3 . Despite preliminary achievements in controlling the anionexchange process of CsPbX 3 perovskites, several key issues have not been clarified in previous studies.…”

“…They found that anion interdiffusion could lead to the transition from the CsPbCl 3 /CsPbBr 3 heterojunction into the halide gradient CsPb­(Br x Cl 1– x ) 3 nanowires. Li et al utilized the solid–solid anion-exchange process to prepare epitaxial heterojunctions in yellow-phase Y-CsPbI 3 nanowires . They found that the anion-exchange reactions drive the structural transition from Y-CsPbI 3 to black-phase CsPb­(I x Br 1– x ) 3 .…”

Bandgap-Engineered CsPbBr3xI3–3x Alloy Nanowires for Broadly Tunable Nanoscale Lasers

“…Therefore, integrating different components to construct semiconductor alloys with flexible bandgaps has become increasingly challenging in recent years. ,− Presently, adjusting the composition by ion exchange has been proven to be an effective method for fabricating semiconductor alloys. − In general, the ion exchange reaction is driven by the ion concentration difference between the reactant and the reaction environment, and the alloy material is formed by the diffusion of high-concentration ions in the reaction environment in the low-concentration reactant . Due to the advantages of simple operation and fine adjustment of physical properties, the ion exchange method has played a crucial role in the development of semiconductor materials. ,, It has been a common method to synthesize homogeneous alloys, ,,, core–shell heterostructures , and nanowire (NW) heterostructures. − Perovskite has a soft and dynamic crystal lattice because of its fragile ionic bonds and high concentration of vacancies. ,, Moreover, perovskite materials have low defect formation energy, which allows ion diffusion and migration in the lattice and acts as an ideal material for ion exchange reactions . In addition, halide perovskites have the advantages of long carrier diffusion length, ,,− high PL quantum yield, − and high defect tolerance, − which make them ideal candidates for next-generation optoelectronic circuits.…”

Field-Induced Transport Anisotropy in Single-Crystalline All-Inorganic Lead-Halide Perovskite Nanowires

“…Single-crystalline perovskite nanostructures offer an intrinsic platform for the investigation of ionic movement on a microscopic scale. Research has shown that the reduction of dimensionality may cause significant difference in ionic behavior in one-dimensional (1D) nanowires (NWs) and 2D nanoplates. , In addition, combined with scanning probe measurements, the coupled ionic and optoelectronic transport process can be spatially and temporally resolved, , so that the microscale ionic transport mechanism can be revealed.…”

“…Research has shown that the reduction of dimensionality may cause significant difference in ionic behavior in one-dimensional (1D) nanowires (NWs) and 2D nanoplates. 32,33 In addition, combined with scanning probe measurements, the coupled ionic and optoelectronic transport process can be spatially and temporally resolved, 34,35 so that the microscale ionic transport mechanism can be revealed. In this work, we investigated the ion-drift-induced giant switchable photovoltaic effect in all-inorganic perovskite NW devices.…”