Researchers from UNSW and DAS Solar developed a zero-busbar metal grid optimization approach for tunnel oxide passivated back-contact (TBC) silicon solar cells, enabling more efficient current collection at the rear surface while reducing silver consumption by 3–4 mg/W. The first TBC cells produced in mass manufacturing using this technique have demonstrated efficiencies exceeding 27%.
The TBC cell
Image: DAS Solar
A research team comprising scientists from the University of New South Wales (UNSW) in Australia and Chinese PV manufacturer DAS Solar have developed a new technique for the optimization of metal grid design of silicon back contact (BC) solar cells applying tunnel oxide passivated contact (TBC) at the rear surface.
The cell is based on a zero-busbar (ZBB) design, which the scientists said required significantly lower silver (Ag) content for metallization.
“Compared with the multi-busbar (MBB) schemes, the ZBB design cuts silver paste consumption by around 3-4 mg/W,” the research’s lead author, Dengyuan Song, told pv magazine. “The specific value varies slightly according to different metallization pattern designs of solar cells. Such a reduction in silver consumption is highly significant and practically remarkable. In particular, under the current frequent fluctuations in silver prices, lowering silver consumption plays a vital role in stabilizing production costs, and supporting the large-scale industrialization of TBC solar cells.”
“Supported by advanced solar cell simulation technology from UNSW, DAS Solar began mass production of ZBB TBC cell technology in early to the second half of 2025. The series welding equipment, soldering processes, and silver pastes have been fully optimized and are ready for industrial-scale manufacturing,” Song went on to say. “At present, DAS Solar has realized large-scale production of TBC cells with silver consumption of approximately 6 mg/W. The peak conversion efficiency of premium batches in mass production exceeds 27%, which further proves that ZBB technology possesses excellent cost performance.”
The 160-μm-thick ZBB TBC cell has dimensions of 182 mm × 105 mm. The front surface is textured with random upright pyramids at a 53° base angle and passivated using an aluminum oxide (Al₂O₃)/silicon nitride (SiNₓ)/silicon dioxide (SiO₂) stack. The inclusion of a low-refractive-index SiO₂ layer further reduces front-surface reflectance.
Image: DAS Solar
At the rear side, the device relies on p-type polycrystalline silicon, n-type polycrystalline silicon, and an undoped gap region. The p-poly and n-poly regions are planar to enhance surface passivation quality.
Using SunSolve for optical modelling and Quokka3 for electrical modelling, the academics measured the performance of the ZBB TBC cell and compared it to that of a reference device built with typical electrical contact pads used as current collection and interconnection points.
Optical results indicate that current generation is largely insensitive to finger width, but decreases slightly as finger pitch increases due to reduced light trapping. For pad-based designs, performance was primarily found to be limited by busbar-related losses, making wider and more numerous busbars and pads beneficial for efficiency. In contrast, zero-busbar (ZBB) designs shift current collection to fingers, where losses scale more strongly with finger geometry, favoring larger busbar segmentation and efficient current routing.
Across both architectures, reducing finger width via improved screen-printing technology offers clear efficiency gains. Pad-based cells were found to require at least 11 mg/W of Ag paste, while ZBB cells maintain similar efficiency at 7 mg/W.
“The absolute efficiency gain of ZBB over pad-based TBC is at least 0.1%, which would significantly increase if Ag paste consumption were below 10 mg/W. From the reduction of Ag paste consumption point of view, ZBB configuration is definitely advantageous, although the increased challenge of interconnection and module reliability requires careful examination,” the academics concluded.
The new methodology was described in “Grid Optimization of Tunnel Oxide Passivated Back Contact Silicon Solar Cells,” published in Progress in Photovoltaics.
In another recent study conducted with UNSW, DAS Solar unveiled a new circuit-model–based method to accurately detect hot-spot risks in TOPCon back-contact modules, overcoming limitations of the IEC 61215 approach caused by low shunt resistance.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.
More articles from Emiliano Bellini
Please be mindful of our community standards.
Your email address will not be published. Required fields are marked *
Comment *
Name *
Email *
Website
Save my name, email, and website in this browser for the next time I comment.


Δ
By submitting this form you agree to pv magazine using your data for the purposes of publishing your comment.
Your personal data will only be disclosed or otherwise transmitted to third parties for the purposes of spam filtering or if this is necessary for technical maintenance of the website. Any other transfer to third parties will not take place unless this is justified on the basis of applicable data protection regulations or if pv magazine is legally obliged to do so.
You may revoke this consent at any time with effect for the future, in which case your personal data will be deleted immediately. Otherwise, your data will be deleted if pv magazine has processed your request or the purpose of data storage is fulfilled.
Further information on data privacy can be found in our Data Protection Policy.
Legal Notice Terms and Conditions Data Privacy © pv magazine 2026
Δ
This website uses cookies to anonymously count visitor numbers. View our privacy policy. ×
The cookie settings on this website are set to “allow cookies” to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click “Accept” below then you are consenting to this.
Close

source