Investigating PID shunting in polycrystalline silicon modules via multiscale, multitechnique characterization. (27th February 2018)

• Record Type: Journal Article
• Authors: Harvey, Steven P.; Moseley, John; Norman, Andrew; Stokes, Adam; Gorman, Brian; Hacke, Peter; Johnston, Steve; Al‐Jassim, Mowafak
• Is Part Of: Progress in photovoltaics. Volume 26:Number 6(2018)
• Page Start: 377
• Page End: 384
• Publication Date: 2018-02-27
• Subjects: PID -- TOF‐SIMS -- EBIC -- polysilicon -- reliability; Solar cells -- Periodicals; Photovoltaic cells -- Periodicals; Solar power plants -- Periodicals; 621.31245
• DOI: 10.1002/pip.2996
• Languages: English
• ISSNs: 1062-7995

Abstract

Abstract: We investigated the potential‐induced degradation (PID) shunting mechanism in multicrystalline‐silicon photovoltaic modules by using a multiscale, multitechnique characterization approach. Both field‐stressed modules and laboratory‐stressed mini modules were studied. We used photoluminescence, electroluminescence, and dark lock‐in thermography imaging to identify degraded areas at the module scale. Small samples were then removed from degraded areas, laser marked, and imaged by scanning electron microscopy. We used simultaneous electron‐beam induced current imaging and focused ion beam milling to mark around PID shunts for chemical analysis by time‐of‐flight secondary‐ion mass spectrometry or to isolate individual shunt defects for transmission electron microscopy and atom‐probe tomography analysis. By spanning a range of 10 orders of magnitude in size, this approach enabled us to investigate the root‐cause mechanisms for PID shunting. We observed a direct correlation between recombination active shunts and sodium content. The sodium content in shunted areas peaks at the SiN X /Si interface and is consistently observed at a concentration of 0.1% to 2% in shunted areas. Analysis of samples subjected to PID recovery, either activated by electron beam or thermal effects only, reveals that recovery of isolated shunts correlates with diffusion of sodium out of the structural defects to the silicon surface. We observed the role of oxygen and chlorine in PID shunting and found that those species—although sometimes present in structural defects where PID shunting was observed—do not play a consistent role in PID shunting. Abstract : Using multitechnique, multiscale characterization—across a range of 10 orders of magnitude—we investigated root‐cause mechanisms of shunting in polysilicon modules due to potential‐induced degradation. We observed that (1) recombination active shunts and sodium content are directly correlated; (2) oxygen is sometimes, but not always, present at shunt locations; and (3) out‐diffusion of sodium to the surface leads to shunt recovery.