The interparticle distance limit for multiple exciton dissociation in PbS quantum dot solid films

Area of Science:

• Materials Science
• Nanotechnology
• Photovoltaics

Background:

• Efficient charge transfer in quantum dot (QD) films is crucial for advancing quantum dot solar cells (QDSCs).
• The behavior of multiple exciton dissociation in QD solid films remains poorly understood, hindering performance optimization.
• Investigating charge transfer dynamics is essential for harnessing photogenerated excitons effectively.

Purpose of the Study:

• To systematically investigate the multiple exciton charge transfer behavior in PbS QD solid films.
• To elucidate the relationship between interparticle distance and exciton charge transfer rates.
• To determine the critical interparticle distance for efficient multiple exciton extraction.

Main Methods:

• Ultrafast transient absorption spectroscopy was employed to study charge transfer dynamics.
• Systematic investigation of PbS QD solid films with varying interparticle distances.
• Quantification of charge transfer tunneling constants for single, biexciton, and triexciton dissociation.

Main Results:

• Multiple exciton charge transfer rate exponentially increases as interparticle distance decreases.
• Biexciton and triexciton dissociation occur via charge transfer tunneling, similar to single excitons.
• Charge tunneling constants were determined: β1: 0.67 ± 0.02 nm⁻¹, β2: 0.68 ± 0.05 nm⁻¹, β3: 0.71 ± 0.01 nm⁻¹.
• An interparticle distance limit of ≤4.3 nm was identified for rapid multiple exciton charge transfer, preventing Auger recombination.

Conclusions:

• Multiple exciton charge transfer is distance-dependent and enhanced at shorter interparticle distances.
• Efficient extraction of multiple excitons requires interparticle distances ≤4.3 nm to precede Auger recombination.
• This finding provides a critical condition for utilizing multiple excitons in PbS QD films for QDSCs.