Atomic structure and structural disorder vs. device efficiency in Kesterite monograin solar cells with S/(S + Se) ≈...

Area of Science:

• Materials Science
• Solid State Physics
• Renewable Energy

Background:

• Cu2ZnSn(S,Se)4 (CZTSSe) is a promising kesterite absorber for solar cells.
• Understanding intrinsic point defects and cation disorder is crucial for improving CZTSSe performance.
• Off-stoichiometry significantly influences defect formation and device efficiency.

Purpose of the Study:

• To directly quantify Cu/Zn disorder and intrinsic point defects in CZTSSe monograins.
• To correlate atomic-scale defect structures with photovoltaic device performance.
• To establish a quantitative framework for defect engineering in kesterite absorbers.

Main Methods:

• Neutron powder diffraction was employed to analyze CZTSSe monograins with S/(S+Se) = 0.8.
• Chemical composition and off-stoichiometry types (A and B) were determined.
• Defect concentrations (VCu, ZnSn, ZnCu) and their relation to stoichiometry were quantified.

Main Results:

• Monograins exhibited a mixture of A- and B-type off-stoichiometry.
• A-type off-stoichiometry correlated with reduced Cu/Zn disorder and increased VCu.
• ZnSn defect concentration increased with B-type off-stoichiometry, while ZnCu antisite defects increased with deviation from stoichiometry.
• Lowest combined defect concentration, near stoichiometry and the A-type line, correlated with highest photovoltaic efficiency.
• Lower optical band gap CZTSSe solar cells demonstrated enhanced stability.

Conclusions:

• Defect engineering in kesterite absorbers can be guided by a quantitative framework linking atomic-scale defects to device performance.
• Minimizing specific defects (e.g., ZnCu antisites) and controlling off-stoichiometry are key to enhancing solar cell efficiency.
• A trade-off exists between optical band gap and solar cell stability, with lower band gaps offering better stability.