RESEARCH ON EL IMAGE BLACKENING OF SOLAR CELL CUTTING SURFACE IN HALF-PIECE PERC PV MODULES
Compared with whole PV modules,half-piece PV modules have higher output power and superior reliability.However,when conducting electroluminescence(EL)testing on such PV modules,it is found that the problem of EL images blackening on the cutting surface of solar cells frequently occurs.This paper first introduces the structure and sintering process principle of PERC solar cells,as well as the EL imaging principle.Then,through experiments,the appearance,silver aluminum contact resistance,and microstructure of overlap between back field and back electrode of the solar cell detecting by scanning electron microscopy(SEM)in the half-piece PERC PV module are analyzed and studied to infer the reason for the EL image blackening on the cutting surface of the solar cell.Then,a verification experiment is conducted to investigate the cause,and improvement measures are proposed for the contact effect at the overlap between back field and back electrode of solar cells,thereby enhancing the yield of PV modules product.The research results show that:1)The obvious tearing gap at the overlap between back field and back electrode is the main reason for the EL image blackening of the solar cell cutting surface in the half-piece PERC PV module.Silver and aluminum undergo a fusion reaction due to high-temperature expansion,resulting in a high degree of alloying caused by excessive reaction.During cooling,the thermal expansion coefficients of silver and aluminum are different,and the silver aluminum paste will shrink during cooling,causing tearing at the overlap between back field and back electrode,resulting in gaps and voids,which deteriorates the silver aluminum contact effect,severely increases the silver aluminum contact resistance value,causes abnormal current transmission,and ultimately leads to EL image blackening of the half-piece PERC solar cell cutting surface.2)By controlling the peak sintering zone in the sintering temperature of the PERC solar cell sintering process,the silver aluminum contact resistance at the overlap between back field and back electrode can be reduced,improving the contact effect at that location,thereby improving the EL image blackening on the cutting surface of half-piece PERC solar cells,and ultimately improving the product yield of half-piece PERC PV modules.
PERC PV moduleshalf-piece technologysolar cell cutting surfaceoverlap between back field and back electrodesintering temperaturesilver aluminum contactEL image blackening
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