As the monocrystalline PERC back passivation technology has almost reached the hat of its conversion rate (around 23.5%), with an achieved efficiency of around 22.5% in batch production, the heterojunction with intrinsic thin-film (HJT) technology is widely placed most expectations for next generation solar cell technology in the solar photovoltaic (PV) world. Many believe HJT will win in competition and become the dominator in next generation solar cell.
However, to become the true winner and realize commercialization with mass output, HJT has to remove several obstacles lying ahead of the march, including the high cost of N-type silicon wafers, high consumption of silver paste and module encapsulation loss.
At this point, another technology, the Metal Wrap Through (MWT) stretches out a helping hand.
Only a few days ago, the long-term MWT advocator, China based Sunport Power announced publicly: “considering the perfect combination of MWT and HJT which can be achieved, Sunport remains open to any company for technical cooperation of MWT and HJT to jointly promote the development of HJT technology.”
Dr. Zhang Fengming, founder and president of Sunport Power expressed his view that “the 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 efficient MWT+HJT solar cells, with not only improving cell conversion efficiency, but also help in cost reduction per watt.”
Taking Sunport’s recently launched MWT+HJT products — C-Pro series as an example, the C-Pro series products are N-type monocrystalline based high-efficiency solar cells which present advantages of the combination of MWT and HJT. The conversion efficiency inherits advantage of both of MWT and HJT, and to an impressive high figure of 25% for products in batch production. Meanwhile, the C-Pro series realize the manufacturing process of super-large size (G12: 210mm*210mm) and ultra-thin in thickness (<120μm) of silicon wafer, which successfully reinforce the power of a single piece of cell to 11W. In summary, with higher conversion rate of MWT+HJT combined cell than competitors, 2.5% higher than normal PERC cell, 0.5-1% higher than normal HJT cell, and also thinner thickness of wafer used by at least 20% compared to conventional cell, which significantly saves silicon cost, and 20% cut off for silver paste consumption, the unit cost of solar cell can be reduced by 10% per watt, and this ensures the technology keep strong competitiveness and remain domination in future.
Another obstacle for production of HJT module is the encapsulation process in which conventional high temperature welding has to be avoided due to utilization of low temperature silver paste on HJT cell. However, this featured difficulty can be easily solved by the advanced 2-D encapsulation scheme of “conductive backplane + conductive adhesive” developed by Sunport Power and utilized on its MWT module. This plane 2-D stress-free encapsulation methodology, which was derived from the SMT electronic encapsulation industry, was developed by Sunport through continuously dedicated R&D investment and eventually applied to MWT cell encapsulation. With help of this technology, the application of welding strip and high temperature welding process in conventional cell encapsulation can be fully eliminated.
Meanwhile, as eliminating the stress generated by the welding strip and welding process, and the low temperature curing process of conductive adhesive also fits perfectly with the electrode of the low temperature silver paste of the cell, which supports ultra-thin silicon wafer applications (<120μm) and reduction of paste consumption (no need for long silver main busbar), the encapsulation loss is significantly reduced, and the weather ability and reliability of the module products are greatly improved.
The integration of MWT+HJT technology gives full play to their respective technical advantages and solves the major problems of commercialization of HJT technology, and improves the conversion efficiency and reduces the production cost as well. We can say that the MWT+HJT technology is the ultimate combination of “super efficiency” and “low cost”, and makes them the best partner of each other.
According to study by Sunport Power, the reduction on module single watt cost with utilization of MWT+HJT is as high as RMB0.15 compared with conventional HJT module. Like Dr. Zhang once said: “‘MWT+HJT’ is a perfect integration of the most advanced module encapsulation process and solar cell technology of the solar PV industry.”