Energy Dispersive Spectrometry Analysis of a CIGS Solar Cell

Energy Dispersive Spectrometry Analysis of a CIGS Solar Cell

Importance of Topic

Copper indium gallium diselenide (CIGS) thin-film solar cells offer high conversion efficiencies while requiring thinner and less costly substrates compared to silicon devices. Accurate elemental characterization of layered CIGS structures is critical to ensure reproducible electrical performance and optimize manufacturing processes. Energy dispersive spectrometry (EDS) in the scanning electron microscope (SEM) provides spatially resolved compositional data essential for quality control and research in photovoltaics.

Study Objectives and Overview

This study employed the Thermo Scientific NORAN System 7 EDS to map and quantify the elemental distribution within a commercial CIGS solar cell. Both planar and cross-sectional analyses were performed to:

• Identify individual layer compositions
• Assess substrate and contact materials
• Determine layer thickness and uniformity

Used Methodology and Instrumentation

Planar-view analysis was conducted at 20 kV accelerating voltage to detect surface layers and delaminated CIGS fragments. Cross-sectional samples were prepared by epoxy mounting and polishing, then analyzed at 5 kV to minimize interaction volume and charging effects. The SEM was equipped with a tungsten filament electron source and a NanoTrace SiLi detector. Data acquisition modes included Point-and-Shoot spectral analysis and Spectral Imaging mapping. Thermo Scientific COMPASS software facilitated phase analysis and quantitative mapping.

Main Results and Discussion

Planar analysis revealed that the top CIGS layer contained major In and Se peaks with smaller amounts of Cu, Ga, Zn, Cd, S, and O. Underlying metallic contacts consisted of Mo and Ag-based paint in localized regions. Cross-sectional low-magnification mapping confirmed the presence of polymer encapsulants, Fe and Al layers, and molybdenum contacts. High-magnification quantitative maps distinguished two Cu-Ga-Se absorber sublayers with differing X-ray intensities and compositions, indicating possible compositional and hardness variations affecting polishing behavior. Layer thicknesses measured approximately 0.9 µm for Mo, 3 µm for the first Cu-Ga-Se layer, and 1.5 µm for the second layer. No CdS or ZnO layers were detected due to their submicron thickness relative to the X-ray generation volume.

Benefits and Practical Applications

• Rapid identification of elemental composition across complex multilayer devices
• Quantitative thickness and uniformity assessment for quality control
• Non-destructive mapping of microstructural variations in thin films

Future Trends and Opportunities

Further improvement in spatial resolution using lower beam energies and advanced detectors may enable detection of ultra-thin junction layers such as CdS and ZnO. Integration with machine-learning algorithms could automate phase identification and defect recognition. In situ EDS analysis during film deposition could offer real-time feedback for process control.

Conclusion

The Thermo Scientific NORAN System 7 EDS provides comprehensive compositional insights into CIGS solar cell structures. By combining planar and cross-sectional analyses with low-voltage mapping and phase software, researchers can resolve multilayer compositions, enhance reproducibility, and guide device optimization.

References

1. D. Abou-Ras et al. Elemental distribution profiles across Cu(In,Ga)Se2 solar-cell absorbers acquired by various techniques. EMC 2008, vol. 1, p. 741.