Spatially resolved evaluation of power losses in industrial solar cells by illuminated lock-in thermography

The principles of a recently introduced measurement technique for power losses in solar cells, illuminated lock-in thermography (ILT), are reviewed. The main advantage of ILT over dark lock-in Thermography (DLT) is measurement under realistic operational conditions of solar cells. The main focus of this paper is to demonstrate the wide range of applications of ILT in identifying the causes of power losses in solar cells. For this purpose different evaluation methods are presented. A method for the evaluation of improvement potentials within a given cell technology is demonstrated. It is shown that different types of series resistance may be localized. Small areas of recombination losses (e.g., grain boundaries) can routinely be detected, which is not possible in dark lock-in thermography. Good correspondence with light-beam-induced current images is found. A realistic evaluation of the impact of recombination losses on solar cell performance is demonstrated on two examples. Finally, process- or treatment-induced recombination losses are investigated. In summary ILT is shown to be an extremely powerful tool in localizing, identifying and quantifying power losses of solar cells under realistic illumination conditions.