LBIC Phase Mapping Detects Solar Module Interconnection Defects
Researchers utilize light beam-induced current phase mapping to identify localized solar cell contact quality issues.
1Innovative Diagnostic Technique
Researchers at Karlstad University have successfully employed light beam-induced current phase mapping to evaluate solar module performance. This non-destructive technique scans a focused laser beam across photovoltaic cells to measure photocurrent responses. Unlike traditional amplitude-based methods, this approach analyzes phase shifts to provide deeper insights into local electrical resistance and contact quality.
2Analytical Modeling Approach
The team developed an analytical equivalent-circuit model to interpret the relationship between measured phase shifts and electrical parameters. By deriving a specific equation, they established how local series resistance directly influences the phase response. This physical framework allows for precise interpretation of data rather than relying on purely empirical correlations between defects and shifts.
3Experimental Setup Details
The experiments utilized an 828 nm laser with 22 μW power and a 6 μm spatial resolution. The laser was modulated at 640 Hz to generate an alternating photocurrent, which was captured using lock-in amplifiers to minimize noise. This precision allowed the team to map internal quantum efficiency and phase shifts effectively.
4Testing Interconnection Quality
Scientists used monocrystalline bifacial silicon cells, cut into halves and laminated using The Tape Solution method. To validate the technique, they intentionally created regions with reduced contact areas by applying less pressure during lamination. This controlled environment allowed for a clear comparison between well-connected areas and those with deliberate electrical defects.
5Quantifying Electrical Resistance
Results showed that phase shifts became more negative post-lamination, indicating increased local series resistance. Regions with high-quality contacts exhibited average phase differences of 150 millidegrees, whereas weakened contact areas reached 250 millidegrees. These findings were confirmed through optical and scanning electron microscopy, which revealed physical gaps in the poorly connected regions.
6Comparison With Existing Methods
The researchers compared their LBIC phase mapping results with electroluminescence imaging to assess diagnostic capabilities. They found that electroluminescence could not easily distinguish the localized resistance variations identified by the phase mapping technique. This highlights the superior sensitivity of the new method in detecting specific interconnection defects within laminated solar modules.
7Scope and Limitations
While the study effectively distinguishes between varying contact qualities, the researchers noted that the current work does not definitively separate partially soldered connections from completely disconnected ones. They acknowledge that while parallel capacitance effects cannot be entirely excluded, changes in local series resistance remain the primary explanation for the observed electrical behavior.
8Future Diagnostic Potential
This methodology offers a robust diagnostic tool for identifying performance losses in photovoltaic modules. Although the study used five-busbar M2 cells, the team believes the approach is scalable to larger industrial solar cells. Future research will likely focus on testing the technique across a broader range of contact conditions to refine its diagnostic precision.
Original article: pv magazine — LBIC Phase Mapping Detects Solar Module Interconnection Defects