Laser scanning of solar cells for the display of cell operating characteristics and detection of cell defects

A new optical scanning technique was developed to map solar-cell operation over the cell area and reveal several types of cell defects. The technique, which makes use of the distributed nature of the cell, an intrinsic property shared by all cells, allows one to detect potentially harmful cracks with a sensitivity greater than any other optical technique reported previously, and it permits one, for the first time, to locate regions of poor metallization. It has also been used to determine efficacy of cell design and to study cell degradation processes. The new scanning technique employs forward biasing of the cell during scanning. Biasing may be achieved through the use of a steady-state light source, or for cells made using conventional semiconductor materials, e.g., silicon and gallium arsenide, the use of an external current source. The scanning technique is nondamaging; it requires no electrical contacts to the cell other than those already present, and it can be used on encapsulated or unencapsulated cells in almost any laboratory or test environment.