Size dependent charge separation and recombination in CsPbI₃ perovskite quantum dots

Area of Science:

• Materials Science
• Photochemistry
• Nanotechnology

Background:

• Cesium lead iodide (CsPbI3) perovskite quantum dots (QDs) are promising for optoelectronic applications due to their light-harvesting and light-emitting properties.
• Efficient charge carrier transfer is crucial for the performance of CsPbI3 QD-based devices.
• Understanding the fundamental processes of charge separation (CS) and charge recombination (CR) in these materials is essential.

Purpose of the Study:

• To investigate the influence of quantum dot size on charge separation and recombination dynamics.
• To explore the relationship between CsPbI3 quantum dot size and charge transfer rates with rhodamine B molecules.
• To elucidate the underlying mechanisms governing size-dependent charge transfer using theoretical models.

Main Methods:

• Transient absorption spectroscopy was employed to measure charge separation and recombination time constants.
• Studies were conducted on CsPbI3 quantum dots with varying average sizes, from 11.8 nm down to 6.5 nm.
• Marcus theory was utilized to analyze the experimental data, incorporating calculated driving forces and electronic coupling strengths.

Main Results:

• A significant decrease in both charge separation (CS) and charge recombination (CR) time constants was observed with decreasing CsPbI3 QD size.
• CS time constants reduced from 872 ± 52 ps (11.8 nm) to 40.6 ± 4.3 ps (6.5 nm).
• CR time constants decreased from 3829 ± 51 ns (11.8 nm) to 1384 ± 54 ns (6.5 nm).

Conclusions:

• Charge transfer properties of CsPbI3 QDs are strongly dependent on their size.
• The observed size-dependent trends align with predictions from Marcus theory, indicating the importance of driving forces and coupling strengths.
• CsPbI3 QDs operate in a weak quantum confinement regime, where size-dependent electronic coupling significantly impacts charge transfer kinetics, unlike strongly confined Cd chalcogenide QDs.