Metal halide solid-state surface treatment for high efficiency PbS and PbSe QD solar cells

Area of Science:

• Materials Science
• Nanotechnology
• Renewable Energy

Background:

• Quantum dot (QD) solar cells offer tunable optoelectronic properties.
• Efficient charge transport and reduced surface ligand carbon content are crucial for high-performance QD solar cells.
• Existing ligand exchange methods often involve sulfur or organic halides, impacting film conductivity and carbon footprint.

Purpose of the Study:

• To develop an efficient layer-by-layer method for preparing lead-based quantum dot (PbE, E = S or Se) solar cells.
• To reduce the carbon content in QD films through surface ligand displacement.
• To enhance carrier transport and power conversion efficiency (PCE) in QD solar cells.

Main Methods:

• Utilized a layer-by-layer approach using metal halide salts (PbI2, PbCl2, CdI2, CdCl2) in dimethylformamide to displace oleate surface ligands.
• Investigated the effectiveness of different metal halide treatments, particularly PbI2, for ligand removal and halide exchange.
• Characterized the resulting QD films for carbon content, work function, band positions, and carrier transport properties.

Main Results:

• The PbI2 treatment effectively removed alkyl surface ligands and exchanged surface chlorides for iodides.
• QD films exhibited significantly reduced carbon content compared to films treated with thiols and organic halides.
• PbS QD films showed deeper work function and band positions, indicating improved charge extraction.
• The method enabled efficient solar cells even at film thicknesses nearing one micron, demonstrating enhanced carrier transport.
• Achieved power conversion efficiencies exceeding 7% for QD solar cells based on PbI2 treatment.

Conclusions:

• The developed layer-by-layer method using metal halide salts is effective for preparing conductive QD solids.
• PbI2 treatment is a superior method for ligand exchange, reducing carbon content and improving electronic properties of PbS QD films.
• This approach leads to enhanced carrier transport and high-performance QD solar cells with PCEs over 7%.