The 0BB technology for solar modules uses ultra-thin low-temperature ribbons, in different technology routes including coating, soldering followed by dispensing, and dispensing followed by soldering
Currently, the low-temperature ribbon used in HJT technology is predominantly composed of bismuth for soldering
Adding rare earth elements to the ribbon composition can enhance corrosion resistance and improve ribbon shelf life
The growing adoption of busbarless (0BB) n-type cells, primarily heterojunction (HJT), driven by the cost optimization potential through significant reductions in silver (Ag) consumption, has fueled the demand for ultra-thin, low-melting temperature PV ribbons for 0BB module production. Proper optimization of the low-melting ribbon solder alloy composition, along with its adaptability to multiple 0BB technology routes, will determine the long-term durability of 0BB modules.
At the recent TaiyangNews annual flagship conference, High-Efficiency Solar Technologies 2024, Mengjiao Liang, Manager of Overseas Markets at YourBuddy, highlighted the company's experience in developing ultra-fine, low-temperature ribbons for 0BB module technologies (see YourBuddy presentation here). She also offered brief insights into the future trends in ultra-thin, low-temperature ribbon development.
0BB module technology consists of 3 different routes: glue dispensing followed by soldering, coating, and soldering followed by dispensing. In the 1st method, a dot of adhesive – either transparent glue or thermosetting glue – is dispensed onto the 0BB cell using screen printing technology, followed by the prefixation of the low-temperature ribbon and lamination. In the 2nd route, which is the IFC coating technology method, the carrier film and low-temperature ribbon are laid over the cell, followed by heating and lamination. In the 3rd route, the low-temperature ribbon is pre-soldered, followed by glue dispensing and lamination. However, the 1st and IFC coating routes are already in mass production, while the 3rd route is in the trial phase.
Liang noted that Risen and Chint have adopted the glue dispensing followed by soldering and IFC coating routes, respectively, for 0BB module production, while Huasun and REC follow the soldering followed by dispensing technology path.
Following a short overview of 0BB technology, the company highlighted a comparative analysis of different 0BB technologies. The glue dispensing followed by soldering technology and IFC technology both have high stability of equipment, while the tensile strength of the soldered ribbon cannot be measured after lamination. Liang added further that pre-welding followed by glue dispensing offers good welding reliability.
Liang emphasized that there are primarily 2 types of low-temperature ribbons used in 0BB modules: the busbar ribbon, which connects solar cell strings to junction boxes and transmits the generated current, and the interconnect ribbon, which connects the cells and collects and transmits the current. Currently, ultra-low temperature ribbons with diameters of 0.18 mm or 0.20 mm and a solder coating composition of SnPbBi26, with a melting temperature range of 93°C to 150°C, are in industrial mass production. Acknowledging the value proposition of low-temperature ribbons – such as low yield strength, high tensile strength, adjustable solder composition, and good wettability and solderability – the company also addressed potential quality-related issues.
YourBuddy noted an offset issue in 0BB technology, primarily observed with the 0.20 mm diameter ribbon. This potential offset can be partially mitigated by employing ribbons with higher yield strength or applying greater tension. The company recommends a 2% tensile ratio with a 0.20 mm diameter ribbon and 106 MPa yield strength to reduce offset issues. The formation of lumps post-lamination can result from several factors: excessive coating thickness, adhesive film (PVB) being superior to EVA, excessively high lamination temperature, or a low melting point of the ribbon, explained the ribbon manufacturer. Liang also emphasized the importance of properly setting the chuck.
YourBuddy’s internal research identified the major quality-related aspects of ultra-thin ribbons: alloy composition, wettability of the solder coating, and corrosion resistance. The use of bismuth (Bi), the main component of low-temperature ribbons, is sufficient to meet short-term demand due to global production capacity. While the SnPbBi composition of the solder alloy performs best in terms of wettability, adding rare earth elements such as phosphorus (P), gallium (Ga), germanium (Ge), and nickel (Ni) to the ribbon composition can enhance corrosion resistance and improve shelf life. The company recommends double-glass-configured 0BB modules over single-glass configurations for long-term reliability.
Liang also provided a brief overview of the company's future product: an ultra-fine triangular ribbon that features thinner diameter, enhanced reflectivity, lower solder melting point, and resistance to hidden cell cracks.