Comparison of photovoltaic module luminescence imaging techniques: Assessing the influence of lateral currents in high-efficiency device structures

• Published in: Solar energy materials and solar cells 2019-04, Vol.192, p.81-87
• Main Authors: Sulas, Dana B., Johnston, Steve, Jordan, Dirk C.
• Format: Article
• Language: English
• Subjects: Contactless electroluminescence; Degradation; Dosage; Electroluminescence; Heterojunctions; Illumination; Imaging; Imaging techniques; Lasers; Lateral current; Luminescence; Material properties; Modules; Partial illumination; Photoluminescence; Photoluminescence imaging; Photons; Photovoltaic module; Photovoltaics; Silicon heterojunction; Statistical correlation
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2018.12.022

We investigate the implications of using partial or patterned illumination for luminescence imaging of photovoltaic modules. Partial illumination induces local photovoltage variations that drive lateral current flow into non-illuminated cell regions, causing the average injection level to vary over the course of luminescence measurement. The extent of lateral current depends on material properties and is especially significant for high-efficiency devices such as the silicon heterojunction with intrinsic thin layer (HIT) modules that we investigate. We compare four module imaging methods including large-area illumination, scanning-laser illumination, contactless electroluminescence, and pattern-illuminated photoluminescence. By evaluating the statistical correlation among the different methods under varying laser fluences, we conclude that most methods converge to similar results at matched photon dose per cell (not laser power density) for the modules that we study, while pattern-illuminated photoluminescence yields distinct images from the other techniques regardless of the illumination power. Our combined analysis using multiple luminescence imaging techniques gives specific insight into the causes of HIT module degradation, including suspected degradation of the transparent conductive oxide and passivation layer. [Display omitted] •Solar module luminescence images may differ for large-area vs. partial illumination.•Partial solar cell illumination causes lateral current that lowers carrier density.•Three imaging techniques converge at matched photon dose (not laser power density).•Pattern-illuminated photoluminescence images differ from other imaging techniques.•Passivation and conductive oxide may degrade in weathered silicon heterojunctions.