Multibandgap quantum dot ensembles for solar-matched infrared energy harvesting

Area of Science:

• Materials Science
• Renewable Energy
• Nanotechnology

Background:

• Crystalline silicon solar cells are nearing their theoretical efficiency limits.
• Harvesting infrared solar photons is crucial for augmenting silicon solar cell performance.
• Lead sulfide colloidal quantum dots (CQDs) offer tunable bandgaps for infrared light absorption.

Purpose of the Study:

• To develop a strategy for efficient infrared energy harvesting to complement silicon solar cells.
• To simultaneously maximize short-circuit current and open-circuit voltage using multi-bandgap CQD ensembles.
• To engineer the density of states in CQD ensembles for optimized solar spectrum matching.

Main Methods:

• Fabrication of multi-bandgap lead sulfide colloidal quantum dot (CQD) ensembles.
• Engineering the density of states by introducing larger-bandgap CQDs into a smaller-bandgap CQD population.
• Characterization of optical response and quasi-Fermi level splitting.

Main Results:

• Achieved a 40 meV increase in open-circuit voltage by shaping the density of states.
• Demonstrated near-unity internal quantum efficiency in the optimized multi-bandgap CQD ensemble.
• Maximized photocurrent to 3.7 ± 0.2 mA cm⁻².
• Attained a record silicon-filtered power conversion efficiency, a 25% relative improvement.

Conclusions:

• Multi-bandgap CQD ensembles effectively enhance infrared light harvesting for solar energy applications.
• Tailoring the density of states in CQDs is a viable strategy to simultaneously boost solar cell performance metrics.
• This approach represents a significant advancement in overcoming the limitations of silicon solar cells.