Solar Energy, Vol.194, 903-912, 2019
Imaging and micro-structural characterization of moisture induced degradation in crystalline silicon photovoltaic modules
Moisture induced degradation in photovoltaic (PV) modules operate via multiple chemical mechanisms commonly identified by the sole use of destructive techniques. However, in such cases, effective use of spatial imaging techniques can aid identification of certain operating mechanisms on the basis of degradation pattern characteristics. This paper presents an approach of imaging the effects of moisture induced degradation in crystalline silicon PV modules under damp heat (DH) test conditions using electroluminescence (EL) and dark lock-in-thermography (DLIT) imaging techniques. The affected regions were extracted for identification of degradation products using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) microstructural characterization technique. Consequently, combination of both imaging and micro-structural characterization techniques were used to propose the mechanism of degradation. The presented approach was instrumental in identification of the effects of moisture induced degradation through imaging techniques, moreover the investigation also provided insights in this field of work. The results present signature image patterns for identification and differentiation of dominant chemical mechanisms under moisture induced conditions viz. tin migration at the finger-wafer interface and formation of silver oxide at cell cracks and edges. The ribbon interconnects was identified as an active site for deposition of oxides from solder material, and aluminium electrode in presence of water as an electrolyte. Moreover, loss in interfacial adhesion between wafer, encapsulant and finger. In addition, material quality, manufacturing distinctions, and module design parameters seem to be responsible for observing different operating mechanisms. Also, the obtained insights were applied for investigation of a 20-year-old aged PV module.
Keywords:Moisture induced degradation;Damp heat test;Photovoltaic modules;Chemical degradation;Electroluminescence imaging;Dark lock-in thermography imaging