Shunt imaging in solar cells using low cost commercial liquid crystal sheets

A simple low cost set-up to determine the location of shunts in solar cells has been developed. Our manual system can reproducibly detect all major shunts in large area reverse biased solar cells at a rate of 1 cell every 12 seconds and allows therefore the imaging of large numbers of cells in a short time. The system is based on the use of commercial liquid crystal sheets which are brought into thermal contact with the solar cell by vacuum. The colour change of the sheet is an indication of the local heating of the cell at shunt locations under reverse bias at typical voltages between -2 and -10 V. The detected shunts are the same as the ones found in lock-in infrared thermography at reverse bias. We discuss some of the system specifications and limitations and give several application examples, with a special emphasis on edge isolation.