Lead halide perovskites have been well explored in various optoelectronic applications due to their unique properties. While issues like toxicity and instabilities hinder their further use, which aroused great interest for the development of alternative lead-free perovskites. Recently, a new family of layered double perovskites (LDPs) with a chemical formula of Cs4M(II)M(III)2X12 provide a new route to solve these problems by combining two main strategies including composition substitution and dimensionality reduction. On the one hand, Pb2+ cations are substituted by a combination of M(II) and M(III) cations with the enlarged composition tuning space. On the other hand, the LDP structure consists of one layer of [M(II)X6]4- octahedra sandwiched by two layers of [M(III)X6]3- octahedra in between two adjacent vacancy layers. However, accessibilities to this class of perovskite-type nanomaterials remain inadequate, hindering their practical implementations in various applications. Here, we report the colloidal synthesis of several types of LDP NCs using a modified hot-injection method, such as Cs4CuSb2Cl12, Cs4MnBi2Cl12, Cs4CdBi2Cl12 and Cs4CdSb2Cl12 LDP NCs. The resulting LDP NCs show unique optical, electronic and magnetic properties and different crystal structures, inspiring to build the composition-structure-property relations between various LDP NCs. Therefore, a series of Cs4CuxAg2-2xSb2Cl12, Cs4Cd1-xMnxBi2Cl12, and Cs4Cd1-xCuxSb2Cl12 perovskite-type NCs (0≤x≤1) are synthesized to investigate the composition-induced crystal structural transformation, and thus, the evolution of electronic bandgap, magnetic ordering and charge carrier dynamics. These transformation processes are explored by experimental observations and further confirmed by theoretical DFT calculations. Taking advantage of both the unique electronic structure and solution processability, we demonstrate that the LDP NCs can be solution-processed as high-speed photodetectors with ultrafast photo-response and narrow bandwidth. We anticipate that our study will prompt future research to design and fabricate novel and high-performance lead-free perovskite-type NCs for a range of applications.

Modulation on composition and structure of lead-free metal halide layered double perovskite nanocrystals

ACS Fall 2021

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