Mixed Lead Halide Passivation of Quantum Dots.

Area of Science:

• Materials Science
• Nanotechnology
• Photovoltaics

Background:

• Infrared-absorbing colloidal quantum dots (IR CQDs) are crucial for enhancing tandem solar cells, particularly perovskite and cSi photovoltaics.
• Current IR CQD solar cells utilize lead iodide passivation, which offers incomplete surface coverage.
• Alternative passivation methods using lead chloride or lead bromide present trade-offs between passivation quality and charge transport.

Purpose of the Study:

• To introduce a novel mixed lead-halide (MPbX) ligand exchange strategy for IR CQDs.
• To achieve thorough surface passivation without sacrificing charge transport properties.
• To improve the performance of IR CQD-based solar cells.

Main Methods:

• Development and application of a mixed lead-halide (MPbX) ligand exchange process on PbS CQDs.
• Characterization of passivation and charge transport properties of MPbX-passivated CQDs.
• Fabrication and testing of photovoltaic devices incorporating MPbX-PbS CQDs.

Main Results:

• MPbX-PbS CQDs demonstrate superior passivation (43 ± 5 meV Stokes shift) and charge transport (4 × 10^-2 cm² V^-1 s^-1 mobility) compared to single lead-halide passivated CQDs.
• Achieved a record infrared open-circuit voltage (IR V_oc) of 0.46 ± 0.01 V.
• Attained an external quantum efficiency of 81 ± 1% for IR photons (>1.1 µm).
• Demonstrated a 1.7× improvement in power conversion efficiency for IR photons compared to controls.

Conclusions:

• The mixed lead-halide ligand exchange is an effective strategy for simultaneous surface passivation and enhanced charge transport in IR CQDs.
• This advancement significantly boosts the performance of IR CQD solar cells, particularly in terms of open-circuit voltage and efficiency.
• The developed MPbX-PbS CQDs offer a promising pathway for next-generation photovoltaic technologies.