Inorganic-Cation Pseudohalide 2D Cs₂ Pb(SCN)₂ Br₂ Perovskite Single Crystal

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Two-dimensional (2D) Ruddlesden-Popper (RP) perovskites (A_n+1B_nX_3n+1) typically feature organic spacers between inorganic layers.
• X-site substitution in RP perovskites is less explored compared to A-site substitution.

Purpose of the Study:

• To synthesize and characterize the first inorganic-cation pseudohalide 2D perovskite single crystal.
• To investigate the structural, phase transition, and optoelectronic properties of the new material.

Main Methods:

• Antisolvent vapor-assisted crystallization (AVC) at room temperature.
• X-ray diffraction for structural analysis.
• Temperature-dependent phase transition studies.
• Photodetector device fabrication and characterization.

Main Results:

• Successful synthesis of Cs₂Pb(SCN)₂Br₂, a single-layer (n=1) RP perovskite with space group Pmmn.
• Observation of a kite-shaped octahedron distortion due to SCN^- anions, limiting quasi-2D formation.
• Reversible first-order phase transformation to 3D CsPbBr₃ at 450 K.
• Achieved a low exciton binding energy (160 meV) and demonstrated a photodetector with responsivity of 8.46 mA W^-1 and detectivity of ≈1.2 × 10¹⁰ Jones.

Conclusions:

• Cs₂Pb(SCN)₂Br₂ represents a novel class of 2D perovskites with inorganic cations and pseudohalide anions.
• The material exhibits unique structural features and a reversible phase transition, relevant for temperature-responsive applications.
• The demonstrated photodetector performance highlights the potential of this new 2D perovskite for optoelectronic devices.