Early Stage LID Tester

• At SNEC in Shanghai, LayTec presents its new LID Scope to test solar cells for Light Induced Degradation (LID)
• The device was developed in cooperation with Fraunhofer CSP
• The system is designed based on a concept that electrical current to cell is equivalent to exposure to the light
• The tool applies 10 A current, while subjected temperature ranges between 80 oC to 160 oC depending on testing mode
• The LID tester typically takes 15 minutes to estimate the LID level

German based metrology toolmaker LayTec in-line GmbH, in cooperation with research institute Fraunhofer CSP, has developed a new tabletop tool for monitoring Light Induced Degradation (LID) at cell level. The new tool, called LID Scope, was introduced in early May and presented for the first time at the SNEC tradeshow in Shanghai on May 25. The tool simulates LID conditions in a small testing setup. LID Scope is mainly promoted for quality control and production process optimization.

Indeed, LID has been a major concern for Passivated Emitter and Rear Cell (PERC) architecture, especially for multicrystalline silicon cells. While LID is a cell level issue, the tests are so far accomplished at the module level. LID Scope enables estimating this degradation already at cell level.

Typically, LID is driven by two parameters; photo-generated free-carrier concentration and temperature. However, according to LayTec, researchers at Fraunhofer CSP found in a patent pending process that applying electrical current to the cell is equivalent to exposure to the light. LayTec has given a shape to this idea in the form LID Scope. According to LayTec's president Tobias Schenk, the tool generates free carriers by applying up to 10 A current to the cell, which is nearly equivalent to soaking under 1-Sun illumination. Simultaneously, the system also heats up the cell from about 80 oC to 150 oC. In these simulated degradation conditions, the system monitors drop in the open circuit voltage of the cell, from which the LID degree is estimated (in percentages).

According to Schenk, the typical measurement time is 15 minutes per cell. However, the tool comes with three modes of operation and the above testing procedure falls into a "Quick test" mode where the cell is exposed to 150oC to 160 oC and testing time varies between 10 to 30 minutes. This quick test data is extrapolated to field conditions. A Pass/Fail mode limits testing time to about 5 minutes. Then a Real-life testing sequence allows estimation of LID in quasi field conditions – 80 oC and the testing duration extends to 8 hours.

The LID Scope comes at a list price of €25,000.