Inert gas bubble formation in magnetron sputtered thin-film CdTe solar cells

Area of Science:

• Materials Science
• Solid State Physics
• Computational Materials Science

Background:

• Current Cadmium telluride (CdTe) solar cell production relies on evaporation techniques.
• Magnetron sputtering offers a potentially more cost-effective alternative for CdTe deposition.
• Sputtering processes can lead to unintentional incorporation of working gases into thin films.

Purpose of the Study:

• To investigate the effects of Argon (Ar) incorporation during magnetron sputtering of CdTe solar cells.
• To understand the mechanisms of Ar penetration, diffusion, and void formation in CdTe films.
• To model the exfoliation process of Ar-induced blisters.

Main Methods:

• Experimental deposition of CdTe films using magnetron sputtering.
• Post-deposition treatment with Cadmium chloride (CdCl2) to improve cell efficiency and remove stacking faults.
• Molecular dynamics simulations to determine penetration thresholds and diffusion barriers for Ar and Xenon (Xe) in CdTe.
• Modeling of blister exfoliation.

Main Results:

• Magnetron sputtering leads to Ar incorporation in CdTe films.
• Post-deposition CdCl2 treatment removes stacking faults but causes Ar to cluster, forming voids and blisters.
• Molecular dynamics calculations show higher Ar penetration than Xe, particularly on the (111) surface.
• Diffusion barriers for Ar in zinc-blende CdTe are reduced near clusters, promoting growth; higher, non-Arrhenius barriers are observed in wurtzite.
• Simulations of blister exfoliation reproduce crater formation with raised rims.

Conclusions:

• Argon incorporation during magnetron sputtering of CdTe presents challenges for device stability due to void and blister formation.
• Understanding Ar penetration and diffusion mechanisms is crucial for optimizing sputtering processes.
• Molecular dynamics simulations provide valuable insights into defect formation and surface morphology evolution in sputtered CdTe films.
• The findings explain void expansion after stacking fault removal and the morphology of exfoliated blisters.