Quantitative local current-voltage analysis and calculation of performance parameters of single solar cells in modules

Quantitative characterization of single cells already embedded in modules is performed by a combination of electroluminescence imaging and dark lock-in thermography. Electroluminescence imaging is used to determine the terminal voltages of single cells in modules, and dark lock-in thermography imaging enables the use of quantitative analyses of single solar cells with the software Local I-V 2. This combination yields spatially resolved images of the performance parameters of single cells. To check the reliability of the method also the directly measured voltages of the single cells in a module have been used for Local I-V evaluation and are compared to the results of Local I-V evaluation from voltages determined by EL. The accuracy of the voltage determination in our experiments is about +/- 1% compared to directly measured voltages, leading to an accuracy of the cell parameters such as J(01), U-oc,, efficiency, power, FF, and so on of about +/- 2% using the voltages determined by EL for the Local I-V analysis. With the method introduced it is possible to quantitatively identify the performance of single solar cells in modules reliably and non-destructively, thereby tracking quantitative changes of the cell performance due to degradation processes with high sensitivity and spatial resolution becomes possible. (C) 2016 Elsevier B.V. All rights reserved.