Busbarless connection method

Busbarless solar cells are interconnected using fine metal wires, electrically conductive adhesives, or embedded ribbons, ensuring both electrical contact and mechanical adhesion without traditional busbars.

Metal Wire Interconnection

In busbarless modules, metal connecting wires are used to link the individual cells. The process involves cutting wires to the required length, positioning them on the cell fingers, and welding or soldering them to form a stable electrical connection. Adhesive points are applied on the front and back of the cell string to reinforce mechanical stability, and curing ensures the connection is solid and reliable. Wire cross-sections can be triangular, circular, or rectangular, typically ranging from 0.005 to 0.55 mm², and may be coated with low-melting-point alloys to facilitate soldering at 120–250°C .

Wire-Embedded EVA Sheet Method

Another approach embeds SnBiAg or copper wires within an EVA encapsulant. The wires are aligned with the cell fingers, and lamination at controlled temperatures (around 170°C) forms ohmic contact while minimizing thermal stress on thin wafers. This method reduces microcracks and maintains high efficiency by optimizing contact resistivity and fill factor .

Electrically Conductive Adhesive (ECA)

ECA pads can replace busbars entirely, providing both electrical contact and mechanical adhesion. Low-temperature ECA processes allow decoupling of electrical and mechanical functions, reducing the amount of silver required and minimizing material costs. Adhesive droplets are applied to each finger, and curing ensures sufficient bonding strength without compromising electrical performance .

Measurement and Calibration Considerations

For testing busbarless cells, specialized contacting units are used to measure current-voltage characteristics accurately. Multiple contact bars or wires are positioned along the fingers to replicate the effect of full-area contact, ensuring consistent fill factor measurements across different laboratories .

Summary

Busbarless solar cell interconnection relies on fine metal wires, embedded ribbons, or ECA pads instead of traditional busbars. Key considerations include:

• Ensuring low contact resistivity and high fill factor
• Minimizing thermal and mechanical stress during lamination or soldering
• Providing mechanical adhesion through adhesives or encapsulants
• Optimizing wire geometry and placement for reliable series connections These methods enable high-efficiency, low-cost, and mechanically robust busbarless solar modules suitable for modern photovoltaic applications .