Connectivity-Dependent Exciton-Phonon Coupling in Cesium Bismuth Halide Quantum Dots

Area of Science:

• Materials Science
• Quantum Dots
• Solid-State Physics

Background:

• Metal halide perovskites are crucial materials with properties dictated by their fundamental building blocks: metal halide octahedra.
• Understanding the structure-property relationships in perovskite quantum dots (QDs) is essential for their application in optoelectronics.

Purpose of the Study:

• To investigate how the connectivity of bismuth halide octahedra in Cs3Bi2Br9 and Cs3Bi2I9 quantum dots affects their electronic and optical properties.
• To elucidate the role of octahedra connectivity in exciton-phonon interactions and carrier relaxation dynamics.

Main Methods:

• First-principles calculations were employed to analyze the impact of octahedra connectivity on wave function symmetry, Huang-Rhys factor, and exciton-phonon coupling.
• Quantum dots were synthesized using a ligand-mediated transport method.
• Transient absorption spectroscopy was used to experimentally verify the theoretical findings and compare exciton dynamics in Cs3Bi2Br9 and Cs3Bi2I9 QDs.

Main Results:

• First-principles calculations revealed that bismuth halide octahedra connectivity significantly influences wave function symmetry and exciton-phonon coupling.
• Experimental results showed strong coupling between phonons and the electronic state in Cs3Bi2I9 QDs, leading to rapid carrier relaxation.
• Cs3Bi2Br9 QDs did not exhibit equivalent phonon involvement in band-edge absorption and exciton relaxation, indicating a lack of strong exciton-phonon coupling.

Conclusions:

• The connectivity of bismuth halide octahedra is a critical factor in tuning exciton-phonon coupling in perovskite quantum dots.
• Structural engineering of perovskite nanomaterials offers a pathway to control exciton relaxation and recombination processes.
• These findings provide insights into designing advanced perovskite-based optoelectronic devices.