Characterization of defects

Authors: Archana Sinha/Rajesh Gupta (IITB)
 

Characterization of defects in PV devices is very important for the improvement of their performance over the long term.
A fast, efficient and non-destructive method has been developed for the detection and characterization of delamination in PV modules using active infrared thermography approach. Thermal image and transient thermal contrast evolution profile provide the qualitative as well as quantitative estimation of the severity of delamination in PV modules. This method can be applied in the production unit and outdoor field conditions.

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Fig. (a) Thermal image of delamination, (b) transient thermal profiles at delamination and non-delamination region, and (c) absolute thermal contrast evolution profile for delamination

In order to have spatially-resolved characterization of solar cells and modules, techniques like light beam induced current (LBIC), electroluminescence imaging (ELI) and lock-in thermography (LIT) have been used under different operating conditions which enhance their capabilities to identify the various types of defects and design failures in PV modules responsible for power loss.

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Fig. (a) Limited-LBIC: 2D map and central line profile of a-Si mini-module consisting of 4 cells, (b) EL images at Isc and 1/10th Isc, (c) LIT images: FB-DLIT, RB-DLIT, Voc-ILIT, Jsc-ILIT

This study involves the analysis of degradation effects in PV modules when they are exposed to harsh environmental conditions. IV characterization, EL and DLIT techniques have been used to investigate the various kind of defects and their growth over the time. By comparing EL and DLIT images, the influence of defects on the electrical parameters can also be studied. This study will be helpful in understanding the performance and reliability of modules and predicting module lifetime.

EL Images
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LIT Images

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Fig. (a) Pre-test images, (b) after 10 days of humidity freeze test, (c) after 40 cycles of temperature cycle test