Scientists from Australia\u2019s University of New South Wales (UNSW) have reduced contaminant-induced degradation in solar cells based on tunnel oxide passivated contact (TOPCon) technology by using copper (Cu) plating on screen-printed devices.<\/p>\n
The research not only enhances the reliability and durability of TOPCon cells under damp heat (DH) and field-like conditions but also highlights the potential for reducing silver consumption and lowering the levelized cost of electricity (LCOE).<\/p>\n
\u201cOur work specifically addresses a key challenge: the sensitivity of TOPCon cells to corrosion, particularly on the front metallization,\u201d said the research\u2019s lead author, Bram Hoex. \u201cTo mitigate this issue, we introduced a 1 \u00b5m Cu plating layer on the front silver grid, creating a protective barrier that significantly reduces corrosion susceptibility. By conducting our experiments at the cell level, rather than the module level, we were able to accelerate the testing process by up to two orders of magnitude. This allowed us to obtain faster results and perform detailed failure analysis, which greatly improved the efficiency of our research and development cycle.\u201d<\/p>\n
The researchers explained that plated-Cu contacts capped with silver (Ag) or tin (Sn) are used to prevent contaminants from infiltrating the contacts themselves and causing oxidation, as well as to improve the soldering process in TOPCon cells.<\/p>\n
The experimenters used bifacial nine-busbar (9BB) 158 mm TOPCon solar cells based on carrier-selective passivating contacts (CSPCs) made of polysilicon and silicon monoxide (poly-SiOx) and a screen-printed silver grid on the rear side, as well as on a boron-doped emitter passivated with aluminum oxide (AlOx) and silicon nitride (SiNx) and another screen-printed silver grid on the front side.<\/p>\n
The plating process, which can result in sodium chloride (NaCl)-induced degradation in TOPCon devices, especially on the front side, was done on screen-printed solar cells using a Conifer plating tool. \u201cDuring the plating process, the rear side completely contacted the cathode electrode, and the front side was immersed in the plating solution (CuSO4),\u201d the academics said.<\/p>\n
\u201cA bias-assisted light-induced plating (LIP) was applied with an around 150 mA constant current and illumination during the process.\u201d<\/p>\n
The tests showed that the plated cells demonstrated an initial efficiency improvement of around 0.39% rel, attributed to reduced grid resistance and increased fill factor.<\/p>\n
\u201cAfter 6 hours of DH testing, unprotected cells showed over 80%rel efficiency degradation, while Cu-plated cells retained performance with only approximately 11.5%rel efficiency loss,\u201d Hoex explained. \u201cTransfer length method (TLM) measurements revealed a 10-fold increase in contact resistivity for bare cells within just 0.5 hours of testing, whereas Cu-plated cells maintained much lower resistivity levels over extended testing periods.\u201d<\/p>\n
Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis confirmed that Cu plating filled voids in the silver contact, creating a denser, more robust interface that prevents contaminant penetration and reduced parasitic recombination.<\/p>\n
\u201cConsidering the results of this accelerated test, we conclude the plated-Cu layer can effectively alleviate NaCl-induced degradation under DH conditions and highly improve the device stability,\u201d the scientists concluded. \u201cThe contact resistivity of NaCl-exposed bare cells was already 1 to 2 orders of magnitude higher than that of plated cells after just 2 h of DH testing, explaining most of the loss in fill factor.\u201d<\/p>\n