Thin-film photovoltaic (PV) modules often suffer from a variety of parasitic resistive losses in transparent conductive oxide (TCO) and absorber layers that significantly affect the module electrical performance. This paper presents the holistic investigation of resistive effects due to TCO lateral sheet resistance and shunts in amorphous-silicon (a-Si) thin-film PV modules by simultaneous use of three different imaging techniques, electroluminescence (EL), lock-in thermography (LIT) and light beam induced current (LBIC), under different operating conditions. Results from individual techniques have been compared and analyzed for particular type of loss channel, and combination of these techniques has been used to obtain more detailed information for the identification and classification of these loss channels. EL and LIT techniques imaged the TCO lateral resistive effects with different spatial sensitivity across the cell width. For quantification purpose, a distributed diode modeling and simulation approach has been exploited to estimate TCO sheet resistance from EL intensity pattern and effect of cell width on module efficiency. For shunt investigation, LIT provided better localization of severe shunts, while EL and LBIC given good localization of weak shunts formed by the scratches. The impact of shunts on the photocurrent generation capability of individual cells has been assessed by li-LBIC technique. Results show that the cross-characterization by different imaging techniques provides additional information, which aids in identifying the nature and severity of loss channels with more certainty, along with their relative advantages and limitations in particular cases.
The characterization of localized shunts in photovoltaic (PV) modules is of major concern due to its impact on the performance and reliability of the modules. Generally, lock-in thermography has been used as an effective non-destructive technique for the characterization of shunts in solar cells; however, it has limited applicability in PV modules. Electroluminescence (EL) imaging is another non-destructive technique for the investigation of shunts, which can be employed in both cells and modules in a much faster and inexpensive way. However, it suffers from a limitation in differentiating shunts from other defects. In this paper, a novel non-destructive approach is presented by combining both techniques, which systematically overcomes the limitations of an individual technique for the characterization of shunts in commercial crystalline silicon PV modules. The dark lock-in thermography technique has been utilized to locate shunts in cells and combined with different aspects of EL imaging applications for the spatial severity analysis of individual shunts. The proposed approach has been successfully employed to investigate the severity of different shunts in modules. This approach can be helpful in locating shunts on the basis of severity, which can be related to the performance, degradation and reliability of PV modules.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.