Polysilicon passivate junctions getting closer to commercial production of c-Si modules
N-type bifacial solar cell structures with front boron diffusion and rear n-type poly-Si passivated junctions.
Image: University of Melbourne
Passivated contacts based on doped polycrystalline-silicon/silicon-oxide junctions could soon be applied to the mass production of crystalline-silicon (c-Si) solar modules, according to a group of researchers from the Australian National University, the University of Melbourne
, and the Chinese module manufacturers GCL System Integration Technology
Commonly called poly-Si junctions, these junctions – which are formed by placing a thin insulating layer of silicon oxide (SiO2) between the c-Si wafer and a highly doped poly-Si layer – have already been tested at the factory level. “The process has been applied to commercial production since 2018,” research co-author Di Yan told pv magazine.
The scientists specified that major manufacturers such as Canadian Solar, Jolywood, SunPower, Trina Solar, and Yingli, as well as Jinko and GCL themselves, have recently implemented R&D activity on this technology. “Of the three largest manufacturers, two have already built pilot lines that produce large-area cells featuring poly-Si junctions with efficiencies above 24.5%,” they stated, adding that the International Technology Roadmap for PV (ITRPV) forecasts the modules manufactured with these junctions may achieve a 35% market share and cell efficiencies of 24% and 24.5% for p- and n-type substrates, respectively, by 2030.
The poly-Si junctions are currently manufactured by combining either doped poly-Si layers and an ultra-thin SiOx layer, or mixing intrinsic and doped hydrogenated amorphous silicon (a-Si:H), and their integration in existing production lines may be easily achieved, according to the researchers. “Early trials, particularly on the n-type TOPCon architecture, suggest [a] rapid, less-than-five-year technology transfer time, due largely to its compatibility with existing production tools and expertise,” they further explained.
For the implementation at the commercial production level, however, several technical and economic hurdles must still be overcome, including the damage that this technology can produce for the polysilicon layers due to the cell’s metallization process. “These challenges are largely responsible for the current, 18% higher manufacturing cost of poly-Si junction cells compared with PERC,” they noted. “Given the early stage of development, this margin is expected to decrease, as informed by the rapid decrease in PERC costs during its first years of production.”
In a statement to pv magazine, Yan explained that this cost gap, however, can be compensated for by PV modules with poly-Si junctions that have at least a 0.4% higher conversion efficiency than conventional PERC modules.
All the techniques and manufacturing processes used for the production of poly-Si junctions are described in the study Polysilicon passivated junctions: The next technology for silicon solar cells? published in Joule. “This paper is a perspective article on the poly-Si passivated junctions technologies for the silicon solar cells rather than including any new research contents on this topic,” Yan stated.
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