Microcrystalline Two-Dimensional Layered Metal-Halide Perovskite Heterostructures
Alexander Schleusener a, Mehrdad Faraji a b, Roman Krahne a
a Italian Institute of Technology (IIT), Via Morego 30, Genova, Italy
b Università degli Studi di Genova, Via Dodecaneso 31, 16146 Genova, Italy
Proceedings of International Conference on Emerging Light Emitting Materials (EMLEM23)
Peyia, Cyprus, 2023 November 13th - 15th
Organizers: Grigorios Itskos, Maksym Kovalenko and Maryna Bodnarchuk
Oral, Alexander Schleusener, presentation 027
Publication date: 18th August 2023

Two-dimensional layered metal-halide perovskites (2DLPs) represent an emerging class of materials where a semiconducting metal-halide octahedral layer is sandwiched between two layers of bulky organic cations. The distinctive structural characteristic of these materials results in high in-plane mobility of excitons and charge carriers, but at the same time, hinders the out-of-plane mobility due to the presence of mostly isolating organic cations [1], [2]. This limits the possibility to study charge and energy transfer processes in vertical heterostructures of this material class. Instead, lateral heterostructures, wherein the composition changes along the in-plane direction, offer an intriguing approach for investigating potential transfer processes at the junction region.

We studied the formation of lateral heterostructures in the system PEA2PbBr4-PEA2PbI4 by developing a facile room-temperature anion exchange method in solution. Ion exchange methods are a common tool used to tune the optical properties in 3D metal-halide perovskites but are underrepresented in the case of 2DLPs [3]. The approach takes advantage of the highly anisotropic structure of 2DLPs, where the bulky organic cations suppress the vertical diffusion of the ions while lateral diffusion is preferred [4]. We observed that 2DLPs can be stabilized in polar solvents such as octanol by exposing them to the corresponding halide salt of the organic cation. Introducing a different halide salt of the cation compared to the parent 2DLP leads to the formation of lateral heterostructures, which initiate at the edges of the microcrystals and propagate toward the center. This process ultimately results in a core-crown-like microstructure containing 2DLPs of two different halides, each contributing to a distinct emission profile. We demonstrate the influence of different processing parameters like the type of ion source and the solvent on the microstructure and optical properties of the resulting heterostructure. The formation of such a heterojunction in the in-plane direction of the semiconducting layer provides an opportunity to control the directionality of the charge carrier or energy flow toward the edges or the center of these microstructures. This, in turn, contributes significantly to a better understanding of the optoelectronic properties in heterostructured 2DLPs.

A.S. acknowledges the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska Curie Funding Program (Project TOGETHER, grant agreement No 101067869).

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