Copper Outdiffusion from Copper-Plated Solar Cell Contacts during Damp Heat Exposure.

Area of Science:

• Materials Science
• Photovoltaics
• Semiconductor Physics

Background:

• Plated copper (Cu) contacts offer a promising alternative to traditional silver contacts for silicon (Si) solar cells.
• Concerns remain regarding the long-term reliability and integrity of these plated Cu contact structures.

Purpose of the Study:

• To investigate the long-term integrity of plated Cu contacts in encapsulated Si solar cells after damp heat (DH) stress.
• To characterize Cu diffusion pathways and potential degradation mechanisms within the solar cell structure.

Main Methods:

• Energy-dispersive X-ray spectroscopy (EDS) was used to analyze Cu outdiffusion through capping layers.
• Secondary ion mass spectrometry (SIMS) was employed to detect Cu presence at the Si surface and within the Si cell bulk.

Main Results:

• Evidence of Cu outdiffusion through tin and silver capping layers, forming a Cu layer on the outer contact surface.
• Detection of elevated Cu levels at the Si surface and in the Si bulk of DH-degraded cells.
• Confirmation that Cu can migrate from contacts into Si during DH stress.

Conclusions:

• Copper is mobile within encapsulated solar cell modules under DH stress.
• Cu migration from plated contacts into the silicon cell is a significant degradation pathway.
• Understanding Cu diffusion is crucial for improving the long-term stability of Cu-contacted Si solar cells.