HJT is the acronym for hetero-junction solar cells. Introduced by Japanese company Sanyo in the 1980s, then acquired by Panasonic in 2010s, HJT is considered as a potential successor to the popular PERC solar cell as of the time of writing, besides other technologies such as PERT and TOPCON.
Due to HJT’s fewer number of cell processing steps, and a much lower cell processing temperatures, this architecture has the potential to simplify the current solar cell manufacturing lines that are currently heavily based on PERC technology.
As shown figure 1, HJT is very different to the popular PERC structure. As a result, manufacturing processes between these two architectures are very different. Compared to n-PERT or TOPCON, which can be upgraded from the current PERC lines, HJT requires significant capital investment in new equipment to start mass productions.
Additionally, as with a lot of new technologies, long-term operation/manufacturing stability of HJT is still under reviewed. This is due to processing challenges such as amorphous Si’s susceptibility to high temperature processes.
HJT demonstrates high solar cell efficiency thanks to the high quality hydrogenated intrinsic amorphous Si (a-Si:H in Figure 1) that can provide impressive defect passivation to both the front and rear surface of Si wafers (both n-type and p-type polarity).
The use of ITO as transparent contacts also improves current flows, while also acting the anti-reflection layer to provide optimal light capturing. Moreover, ITO can also be deposited via sputtering at low temperature, thus avoiding the re-crystallisation of the amorphous layer that will impact the passivation quality of the materials on the bulk Si surface.
In spite of its processing challenges and high capital investments, HJT is still an attractive technology. This technology demonstrates the ability to achieve >23% solar cell efficiency, compared to ~22% shown by TOPCON, PERT and PERC technologies.