With monocrystalline PERC passivation technology approaching the limit of its conversion efficiency at around 23.5%, with an efficiency of around 22.5% in mass production, heterojunction (HJT) with intrinsic thin-film is well placed to become the next generation solar cell technology.
However, for this to happen and for HJT to achieve commercialization at mass production levels, it will need to overcome a number of obstacles in its path, including the high cost of N-type silicon wafers, high consumption of silver paste and module encapsulation loss.
The adoption of Metal Wrap Through technology (MWT) may help in this regard, with Chinese manufacturer and long-term MWT advocate Sunport Power making public its willingness to enter into a technical cooperation arrangement with any company to explore a combination of MWT and HJT to “jointly promote the development of HJT technology.”
Dr. Zhang Fengming, Sunport’s founder and president, commented: “MWT technology can solve many difficulties attached to HJT and greatly improve the commercialization of HJT cells. The integration of MWT and HJT technologies can push the mass production of high efficiency MWT+HJT cells, not only improving cell conversion efficiency, but also reducing cost per watt.”
Taking Sunport’s recently launched C-Pro series of MWT+HJT products as an example, they are based on N-type monocrystalline high-efficiency cells, which combine the advantages of MWT and HJT in reaching a conversion efficiency of an impressive 25% in mass production. Meanwhile, the series adopts the manufacturing process of super-large size (G12: 210mm*210mm), ultra-thin (<120μm) silicon wafers, reinforcing the power of a single cell unit to 11W.
With the combined cell providing a 2.5% and 0.5-1% higher conversion efficiency than a normal PERC and HJT cell respectively and with a wafer at least 20% thinner than that of a conventional cell, there is a significant saving in silicon cost and a 20% reduction in silver paste consumption. This results in the unit cost of a cell being 10% lower per watt, enabling the technology to remain competitive and maintain a position of domination going forward.
Another obstacle for HJT module production is the encapsulation process in which conventional high temperature welding has to be avoided due to utilization of low temperature silver paste on an HJT cell. However, this problem can be easily solved with Sunport’s advanced 2-D encapsulation scheme of “conductive backsheet + conductive adhesive” used on its MWT module. Using this technology, the welding strip and high temperature welding process in conventional cell encapsulation can be completely eliminated.
The elimination of the stress generated by the welding strip and process and the low temperature curing process of the conductive adhesive also fits perfectly with the electrode of the cell’s low temperature silver paste, which supports ultra-thin silicon wafer application (<120μm) and reduction of paste consumption, with no need for a long silver main busbar. The encapsulation loss is significantly reduced, and the reliability and weather resistance of the module significantly enhanced.
The integration of MWT+HJT technologies gives full play to the respective technical advantages of each and solves the major problems of commercialization of HJT technology, improving conversion efficiency and reducing production costs.
According to research undertaken by Sunport, the reduction in single watt cost of a module using MWT+HJT can be as high as RMB 0.15 when compared with a conventional HJT module.