Key takeaways:
Back contact technology is expected to gain market share, with projections exceeding 30% by 2035
Pilot line results show that existing TOPCon lines can be adapted for back-contact production with limited modifications
Key challenges remain in process complexity, yield optimization, and maintaining high Voc levels
While there exist 3 mainstream solar PV technologies, with a fourth on the wane (PERC), TOPCon dominates for the most part. The technology, however, is nearing its limits, and the industry’s gaze has turned to what comes next. Back-contact (BC) technology, with a tiny share of the market currently, is seen as an avenue for higher efficiencies and innovations. It is expected to grow to capture over 20% of market share by 2030 and over 30% by 2035. These figures, according to Florian Buchholz of ISC Konstanz, are already somewhat conservative, suggesting that the actual share of BC could still be higher. This was also mentioned by Radovan Kopecek at the recent TaiyangNews STC.I 2026.
Buchholz, at the TaiyangNews High in Efficiency, Low in Silver: BC Technology from Europe Conference, said that it is evident from the market’s best high-efficiency technologies across various platforms, including TaiyangNews’ TOP SOLAR MODULES, that BC has held the leadership position for quite a long time. The list has been featuring commercially available modules in which BC continues to lead, with multiple upgrades each year. The current top modules feature 25.1% efficiency shared by both AIKO and LONGi.
The recently concluded IBC4EU project, with a budget of more than €17 million and funded by Horizon Europe, aimed to demonstrate an industrially feasible bifacial IBC cell and module technology at the pilot level in Europe. The project involved a consortium of research institutes, materials manufacturers, PV manufacturers, and analysts.
Buchholz from ISC Konstanz presented IBC4EU’s results, banking on solar cell and module research conducted over the last 42 months. As part of the project, both n-type- and p-type-based BC cells were found to show good efficiency potential. The p-type POLO IBC from ISFH presents an efficiency potential of over 25.5%, and n-type polyZEBRA (TOPCon-based) from ISC Konstanz shows efficiencies of over 26%. These technologies have already been transferred to Kalyon PV and FuturaSun for commercial production, respectively.
In polyZEBRA, unlike conventional TOPCon, where the rear is passivated with only SiOx + n-polySi layers, there are additional SiOx + p-polySi layers arranged in an interdigitated format to form the BC structure. polyZEBRA, otherwise termed as TOPCon back-contact (TBC), needs several requirements to be addressed.
Reducing metal-induced recombination: Initially, pastes were improved to reduce J0,metal, which negatively affected Voc. This was mitigated through improvements to the passivation stack and with fast-firing profiles. Different passivation layer combinations were also tested, enabling efficiencies above 25%.
Surface passivation: To achieve excellent surface passivation, various stacked layers were tested on non-metallized cell precursors, reporting over 730 mV implied Voc. This again enables higher cell efficiencies.
Low breakdown voltage: This is important for partial shading behavior. The area between the fingers was experimented with different doping levels, which influence the breakdown curve and voltage of about -3 to -5 V. This allows tunable doping in the gap region based on the module’s final application.
Silver reduction is an important aspect, and since ISC’s ZEBRA technology was commercialized in 2018, alternative materials were applied in such a way that busbars and then fingers were sequentially replaced with copper in commercial scenarios. Cells with screen-printed Ag fingers and Cu busbars were made, delivering an efficiency of about 24.3%. These cells consumed only 4 mg/W of silver. However, a silver reduction of about 83% can be achieved compared to baseline consumption in mainstream manufacturing.
Finally, the industrial feasibility of TBC was evaluated using a pilot line at ISC Konstanz, where laser-based and mask-free processes were employed to structure the rear side. About 2,000 cells were manufactured as part of this pilot. Screen-printing metallization using Ag/Cu pastes was used. It was found that more than 90% of an existing TOPCon production line, with some modifications, can be adapted for TBC manufacturing. Some hurdles still need to be overcome, including maximizing Voc and overcoming tight tolerances in laser processes. Compared to a standard TOPCon line, TBC requires 4-5 additional steps, which may lead to a yield penalty of around 1-1.5%, with higher losses expected during early ramp-up. Despite this, Buchholz, in his conclusion of the talk, titled Key Results of IBC4EU, considers TBC to be quite close to industrial feasibility.
The feasibility of the pilot was also demonstrated by building full-sized modules with 120 M6 half-cells and copper busbars. These modules implemented gapless designs using overlapped cells. The modules exhibited lower fill factor and lower bifaciality due to thicker fingers on the rear side. However, the power output was similar to that of a silver reference module.
