Key takeaways:
Interconnecting BC and 0BB cells remains challenging at the module assembly stage, particularly due to post-solder bowing and the difficulty of soldering ribbons or wires to the cell fingers
Sticky Solar’s tape-based approach attaches wires without heating at the stringing step, accomplishing the interconnection at the lamination process, eliminating soldering altogether
While the technology is compatible with various cell architectures, Sticky Solar is primarily focusing its development on BC applications, with pilot projects and potential local tape manufacturing planned for India
Back contact (BC) cell technology is gaining importance among leading solar manufacturers. However, there are still some challenges at the cell and module levels that need to be addressed before it hits the mainstream.
One such challenge is the stringing of BC cells. The conventional soldering method used for stringing involves temperatures around 240°C. Given that all contacts of BC cells are on the rear side, soldering at this temperature can cause the cells to bow, potentially leading to cracks and breakage issues.
Another hot topic in the solar cell and module segments of the PV industry in 2025 was zero busbar (0BB) technology, driven by the aim of reducing silver use and addressing its rising price. There are several approaches to realizing 0BB. It is somewhat easier at the cell level, as it includes only a change of screen at the screen-printing stage. However, the process becomes quite complex at the module assembly, particularly when interconnecting 0BB cells with a combined tabber and stringer (CTS) tool. The challenge lies in soldering the ribbons to the fine fingers (or pads) of a cell.
Sticky Solar Power, a Sweden-based company offering solutions to the PV industry, focuses primarily on the module assembly side of manufacturing. The company developed a solution it calls ‘The Tape Solution’ (TTS) to enable cell interconnection at the stringing station. The solution primarily focuses on interconnecting BC cells at low temperatures.
Diving into the details, as part of TTS, Sticky Solar developed a stringer that uses tape and copper wires or ribbons that are attached to the fingers or busbars of the cells. Unlike typical stringers that use ribbon soldering to interconnect cells, Sticky Solar uses a proprietary tape to hold the ribbons intact, attached to fingers or busbars. The actual interconnection occurs during the lamination stage, thereby eliminating the need for soldering.
Therefore, in addition to cell and ribbon wires used in the mainstream stringer, Sticky Solar’s stringer also uses its tape. The stringer alone has a footprint of about 5.5 m2, which is about 1/5th the size of its mainstream counterpart. The tool can process 5,000 cells per hour in a single-lane configuration.
The key difference in its TTS approach is that a sheet of tape is slit into strips 5-7 mm wide. Ribbon wires are attached to these tape strips, which are then applied to the cells in series to form a string. Once the desired string length is reached, the string is cut at the end of the stringer and is ready for layup. The laid-up and interconnected strings are then covered with the rear encapsulant and glass stack, preparing the module for lamination. In addition to bonding the module layers, the lamination step also completes the cell interconnection, at a maximum process temperature of 160°C.
Jonas Buddgård, CEO of Sticky Solar, said, “The modules made using TTS have undergone reliability tests, including thermal cycles, damp-heat, humidity, and freezing tests. We ensured that the tape can withstand prolonged UV exposure and does not outgas during lamination.”
According to Sticky Solar, additional comparative cell-to-module (CTM) tests were performed on mini-sized modules made with bifacial HJT cells based on M2 wafers at Fraunhofer ISE. Some of these modules were made using TTS, and others were based on competitors’ interconnection methods. The company claims that modules based on the TTS route delivered 4% higher power than the competitors. This increase in power, according to Buddgård, comes from an increase in output current. He further stated that more tests are planned using clients’ cells to further confirm this result.
The company’s cost analysis indicates that by eliminating soldering at CTS and reducing silver at the cell line, TTS can reduce the cost of making a standard PV module by 5-7% on average. Sticky Solar’s team also noted that its first-generation stringer was suitable for bifacial TOPCon. However, the very first European order it received was for BC cell stringing, which led to a shift in its focus to BC technology. The company also believes TTS is a good fit in 0BB cell processing.
With India shaping up to become one of the emerging markets, Sticky Solar is eyeing this opportunity to establish its presence in the region. The company states that it made a couple of visits to the country as part of this effort, most recently in April 2025, and received an encouraging response from several cell and module manufacturers. Sales Director Andreas Runsten stated, “Some tier 2 Indian module manufacturers showed interest in BC technology and our TTS solution. One or two of these companies might also actively collaborate with us for establishing pilot lines in the near future.”
Encouraged by this, Sticky Solar is also planning to manufacture its tape in India and has already identified potential partners to produce its proprietary tape locally, according to Buddgård. This adds to the advantage of making its solution economically viable for the Indian market.
In conclusion, Sticky Solar stated that based on its assessment, installing its stringer in an existing module line is cost-effective, especially for integrated BC cell and module makers who can save on silver in cell lines, use copper wires for stringing, and potentially reduce the complexity of BC and 0BB module making.