Abstract
Lead-based halide perovskite nanocrystals (NCs) are recognized as emerging emissive materials with superior photoluminescence (PL) properties. However, the toxicity of lead and the swift chemical decomposition under atmospheric moisture severely hinder their commercialization process. Herein, we report the first colloidal synthesis of lead-free Cs4CuIn2Cl12 layered double perovskite NCs via a facile moisture-assisted hot-injection method stemming from relatively nontoxic precursors. Although moisture is typically detrimental to NC synthesis, we demonstrate that the presence of water molecules in Cs4CuIn2Cl12 synthesis enhances the PL quantum yield (mainly in the near-UV range), induces a morphological transformation from 3D nanocubes to 2D nanoplatelets, and converts the dark transitions to radiative transitions for the observed self-trapped exciton relaxation. This work paves the way for further studies on the moisture-assisted synthesis of novel lead-free halide perovskite NCs for a wide range of applications.
Highlights
Lead-based halide perovskite nanocrystals (NCs) are recognized as emerging emissive materials with superior photoluminescence (PL) properties
B enefiting from their reduced toxicity, compositional tunability, and superior structural stability,[1−4] lead-free double perovskites have attracted increasing attention in recent years both in the form of bulk films[5−8] and colloidal nanocrystals (NCs),[9−12] as substitutive materials of leadbased halide perovskites for potential commercial applications, i.e., light-emitting diodes (LEDs),[13] solar cells,[14] and photodetectors.[15]
Cs4CuSb2Cl12 has been successfully synthesized both in the form of a single-crystalline powder[22] and NCs,[23,25] exhibiting a narrow direct bandgap (1.0−1.8 eV) and impressive stability, which still suffers from the high toxicity of the Sb element and the absence of emission at room temperature
Summary
AFirst exciton peak. bEmission peak. cFull width at half-maximum. dBandgap. The X-ray diffraction (XRD) patterns of Cs4CuIn2Cl12 NCs formed in the presence or absence of moisture in the reaction show a negligible deviation from the simulated pattern of bulk. High-resolution TEM (HRTEM) image (Figure 2c) highlights that d-Cs4CuIn2Cl12 NCs possess a well-defined crystalline structure with a lattice d-spacing of 0.376 nm, which is assigned to the (311) crystal plane, highly consistent with the crystalline direction determined from the selected area electron diffraction (SAED) pattern (Figure 2d). The NCs grow in the 2D direction to form nanoplatelets This moisture-assisted shape change has been previously observed for CsPbBr3 NCs.[26] In addition, the morphological transformation from 3D d-Cs4CuIn2Cl12 NCus to 2D wCs4CuIn2Cl12 NPLs is irreversible because the 2D NPLs still dominate the product population after 6 days of storage in a nitrogen-filled glovebox
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