Electronic Modulation in Site-Selective Occupation of Quasi-2D Triangular-Lattice Cs₂CuCl_4–xBr_x Perovskite Probed by Surface-Sensitive Characterization

Abstract

A controllable electronic manipulation in a frustrated magnetic system such as solution-based two-dimensional (2D) all-inorganic perovskites offers a possible route for their integrations with electronic and magnetic devices for their advanced applications. Here, we perform element-specific investigations of an emergent class of quasi-2D all-inorganic perovskites Cs 2 CuCl 4−x Br x with (0 ≤ x ≤ 4) using a combination of synchrotron-radiation photoelectron techniques. Surface-and element-sensitive X-ray absorption spectroscopy spectra of Cu L 2,3 edges indicate strong electronic transition that is largely influenced by their halogen content at room temperature. This implies that site-selective occupation largely dominates the electronic transition across the unoccupied states of these series since chlorine atoms possess a stronger electronegative character than bromine atoms. Moreover, the implication of halogen site is reflected in the valence band of Cl-rich copper perovskite in which the valence band edge is closer to Fermi energy (E F ) than that of the Br-rich compound. Furthermore, X-ray magnetic circular dichroism spectra of mixed ratio and Br-rich compounds exhibit antiferromagnetism at room temperature. These site-specific magnetic-spectroscopic results are corroborated by density functional theory calculations. The strong electronic modulation and the local magnetic spectroscopy results in these solution-based and low-temperature-growth materials will pave the way toward energy-and cost-efficient perovskite devices.

Single Crystals of Mixed‐Cation Copper‐Based Perovskite with Trimodal Bandgap Behavior

“…Regarding to literatures, mixed‐halides of all MA Cu‐perovskites, that is, (CH 3 NH 3 ) 2 Cu(Cl/Br) 4 , are easily exfoliated into two‐dimensional (2D) perovskites [20,21] . On the other hand, mixed‐halides of all Cs Cu‐perovskites, that is, Cs 2 Cu(Cl/Br) 4 with different crystal structures depending on the halogen content, cannot be exfoliated into separated flakes [42–45] …”

“…[20,21] On the other hand, mixed-halides of all Cs Cu-perovskites, that is, Cs 2 Cu(Cl/Br) 4 with different crystal structures depending on the halogen content, cannot be exfoliated into separated flakes. [42][43][44][45] Herein, easily exfoliated 2D mixed-halides of all Cs perovskite are prepared through using excess concentration of cesium bromide (CsBr). Furthermore, based on this tricky point, we exceptionally synthesized and evaluated 2D Cubased mixed-cation perovskite crystals and studied their magnetic and photovoltaic properties.…”

Electronic and Optical Modulation of Pine Tree-like Nanostructures of Gallium Nitride

“…X-ray photoemission spectroscopy (XPS) experiments were carried out using an X-ray source of magnesium Kα with a typical excitation energy output of 1254 eV. Ultraviolet photoemission spectroscopy (UPS) measurements were performed using a VG ESCALab system and an ultrahigh vacuum (UHV) system with a typical base pressure in the range of ∼10 –10 mbar equipped with a gas discharge lamp in which helium gas was introduced into the analysis chamber. , The UV source was unfiltered He Iα (21.2 eV) excitation, and the samples were biased at −5 V to extract the low-energy secondary electron cutoff. The UV light spot size on the sample was about 1 mm in diameter.…”

Mechanochemical Synthesis, Optical and Magnetic Properties of Pb-Free Ruddlesden–Popper-Type Layered Rb2CuCl2Br2 Perovskite

“…So far, reported all-inorganic RP halide phases are Cs 2 PbI 2 Cl 2 , Cs 2 SnI 2 Cl 2 , Cs 2 CdCl 4 , and Cs 3 Cd 2 Cl 7 , some of which showed stimulating optoelectronic and ultralow thermal conductivity along with enhanced solar cell efficiency and stabilities. ,− Recently, transition metals (Fe 2+ , Zn 2+ , and Cu 2+ ) have seen pronounced attention for replacement of toxic Pb in halide perovskites. , Cu-based materials are mainly attractive due to their flexible and tunable structures, resulting from the Jahn–Teller effect of Cu 2+ , improved stability under ambient conditions, and high absorption coefficient in wide-ranging visible regions . Recently, a few reports appeared regarding the synthesis, structural information, specific heat measurement, and electronic properties of 2D all-inorganic Cu 2+ -based halide perovskites, − however, lacking detailed optical studies. In general, the Cu 2+ -based 2D layered analogues are interesting due to their fascinating magnetic properties. − …”