Connectivity-Driven Electronic Structure and Charge Separation in Morpholinium-Based Bi³⁺/Sb³⁺ Halides

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Organic-inorganic metal-halide double perovskites (A₂MM'X₆) exhibit diverse structures and electronic properties influenced by A-site cations and M-site metals.
• The connectivity of M'X₆ octahedra and electronic characteristics are crucial for material functionality.

Purpose of the Study:

• To synthesize and characterize novel morpholinium (MOR)-based halides.
• To investigate the structure-property relationships in these materials, focusing on crystal architecture, charge transport, and optoelectronic behavior.

Main Methods:

• Single-crystal X-ray diffraction for structural determination.
• Density Functional Theory (DFT) calculations for electronic structure and effective mass analysis.
• Photoluminescence spectroscopy to probe electronic transitions and recombination mechanisms.

Main Results:

• Four morpholinium-based halides, (MOR)₂CsBiCl₆ (1), (MOR)₂CsSbCl₆ (2), (MOR)₂KBiCl₆ (3), and (MOR)₂RbSbI₆ (4), were synthesized and structurally characterized.
• Compounds 1 and 2 display anisotropic charge transport with higher electron mobility, while compound 1 shows spatial separation of charge densities, indicative of a Z-scheme heterojunction.
• Compound 3 exhibits suppressed charge mobility due to large Cl···Cl separations, and photoluminescence studies reveal distinct recombination mechanisms in compound 1.

Conclusions:

• The study highlights the critical roles of cation size, lone-pair activity, and halide polarizability in directing the structure and electronic properties of organic-inorganic metal-halide materials.
• These findings provide insights into designing novel materials with tailored optoelectronic characteristics.