Interface Engineering of Cu(In,Ga)Se₂ Solar Cells by Optimizing Cd- and Zn-Chalcogenide Alloys as the Buffer Layer

Area of Science:

• Materials Science
• Solid State Physics
• Renewable Energy

Background:

• Optimizing band alignment at the buffer/absorber interface is critical for high-efficiency Cu(In,Ga)Se2 (CIGS) solar cells.
• Traditional cadmium sulfide (CdS) buffer layers have limitations that necessitate exploration of alternatives.
• Tuning buffer layer composition offers a pathway to improved solar cell performance.

Purpose of the Study:

• To investigate novel buffer layers, specifically zinc-cadmium sulfide selenide (ZnCdSe) and zinc sulfide oxide (ZnSO) alloys, as alternatives to CdS for CIGS solar cells.
• To computationally determine the material properties and band alignments of these alloys using first-principles calculations.
• To identify optimal compositions for enhanced buffer/absorber interface properties and improved CIGS solar cell efficiency.

Main Methods:

• Utilized the special quasi-random structure (SQS) approach to model randomly disordered ZnCdSe and ZnSO alloys.
• Employed first-principles density functional theory (DFT) calculations to investigate formation energies, lattice parameters, band gaps, and band alignments.
• Analyzed the compositional dependence of these properties and their relationship to lattice mismatch and chemical disparity.

Main Results:

• Established linear and trinomial dependencies for lattice parameters, band gaps, and band-edge positions of ZnCdSe alloys with composition.
• Found that ZnSO alloy lattice parameters also exhibit linear dependence on composition.
• Identified optimal composition ranges for ZnCdSe and ZnSO alloys, considering band offsets, band gap, and lattice matching with CIGS absorbers.

Conclusions:

• ZnCdSe and ZnSO alloys demonstrate significant promise as buffer layers for high-efficiency CIGS solar cells.
• These novel alloys offer tunable properties for optimizing the crucial buffer/absorber interface.
• The findings provide a theoretical foundation for the experimental development of these advanced buffer materials.