Electrical and chemical properties of vacancy-ordered lead free layered double perovskite nanoparticles

Amal Sawahreh; Tal Binyamin; Jie Jiang; Oded Millo; Oren Goldberg; Doron Azulay; Ruth Pachter; Lioz Etgar

doi:10.1039/d2nr00565d

Electrical and chemical properties of vacancy-ordered lead free layered double perovskite nanoparticles

Nanoscale. 2022 Mar 7;14(9):3487-3495. doi: 10.1039/d2nr00565d.

Authors

Amal Sawahreh¹, Tal Binyamin¹, Jie Jiang², Oded Millo³, Oren Goldberg³, Doron Azulay³, Ruth Pachter², Lioz Etgar¹

Affiliations

¹ Institute of Chemistry, Casali Center for Applied Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel. lioz.etgar@mail.huji.ac.il.
² Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433, USA.
³ Racah Institute of Physics, The Hebrew University of Jerusalem and the Center for Nanoscience and Nanotechnology, Jerusalem 91904, Israel.

PMID: 35171187
DOI: 10.1039/d2nr00565d

Abstract

In this work we synthesized vacancy-ordered lead-free layered double perovskite (LDP) nanoparticles. This structure consists of two layers of trivalent metal halide octahedra [B(III)X₆]^3- separated by a layer of divalent metal [B(II)X₆]^4- (B is a divalent or trivalent metal). The chemical formula of this structure is based on A₄B(II)B(III)₂X₁₂ where A is Cs, B(III) is Bi, X is Cl and B(II) is a different ratio between Mn²⁺ and Cd²⁺. Well-defined colloidal nanoplates of Cs₄Cd_xMn_1-xBi₂Cl₁₂ were successfully synthesized. These nanoplates show photoluminescence (PL) in the orange to red region that can be tuned by changing the Cd/Mn ratio. High resolution scanning transmission electron microscopy (HR-STEM) and atomic resolution elemental analysis were performed on these lead free LDP nanoplates revealing two different particle compositions that can be controlled by the Cd/Mn ratio. Ultraviolet Photoelectron Spectroscopy (UPS) and scanning tunneling spectroscopy (STS) reveal the band gap structure of these LDP nanoplates. Density functional theory (DFT) calculations show the existence of [MnCl₆]^4- in-gap states. While the absorption occurs from the valence band maximum (VBM) to the conduction band minimum (CBM), the emission may occur from the CBM to an in-gap band maximum (IGM), which could explain the PL in the orange to red region of these nanoplates. This work provides a detailed picture of the chemical and electronic properties of LDP nanoparticles.