Photovoltaic Ribbon: Product Performance Overview and Biotechnology Comparison

PV ribbon is a key component in solar panels and an important factor in improving the efficiency and durability of solar panels (Figure 2). The efficiency and durability of solar panels can only be achieved with PV ribbons properly installed in the solar panel. PV ribbon can also improve solar panel production efficiency and reduce scrap rate.

To ensure the high productivity of the string welding process, very straight, soft and weldable ribbons must be used. In the string welding and wiring process, the placement of the PV ribbon must also be ensured. Interconnecting ribbons necessarily reduces stringer downtime and its scrap rate. Today's high-speed stringers are more demanding on ribbon performance. The three main trends in PV ribbon performance are:

a) The new generation of fully automatic high-output stringers requires more and more stringent tolerances for flux thickness and ribbon straightness;

b) Thinning solar cells require lower yield strength of the ribbon (Rp0.2%);

c) New solar panel designs employ three interconnected ribbons per cell instead of two, reflecting the growing demand for smaller (narrower and thinner) ribbons. This in turn drives capacity expansion of tinning lines for small interconnect ribbons.

Properties and Requirements of PV Ribbon

The conductor or base material in PV ribbon is high-conductivity, high-purity copper (Figure 3). The copper used for PV ribbons is generally copper in the form of ETP, DIP or oxygen-free copper (OFC: CD-110, CD-101, CD-102).

The copper wire is wound in a rolling mill to produce copper strip, followed by tinning/flux plating on the tinning wire. Some manufacturers produce copper strip with an alternative copper strip slitting process, which is generally of lower quality.

The size of the PV busbar bare copper strip (the inlet material of the tinning production line) is 3-6mm wide and 0.2-0.5mm thick. For interconnect ribbon, the dimensions of bare copper ribbon are 1-3mm wide and 0.08-0.2mm thick.

Copper tape tolerances vary by manufacturer. They mainly depend on the type of rolling mill used, the quality of the input material and the manufacturer's process know-how. The following are typical tolerances for manufacturers with rolling capabilities: (a) Width tolerance: ±8μm-±15μm; (b) Thickness tolerance: ±8μm-±13μm.

The mechanical properties of PV ribbon that solar panel manufacturers typically seek are:

Tensile strength: <250MPa

●Elongation:>20%

camber: <0.5% [5mm on 1m long sample]

●Yield strength (Rp0.2%): a) hard>120MPa; b) soft<80MPa; super soft<65MPa

The straightness (also known as camber) of PV ribbon is measured in millimeters from a straight line on a one-meter-long ribbon sample. The large camber is determined by the string welding process, and its range is generally between <8mm/m and <5mm/m.

There are many different types of flux components used in PV ribbons. They depend on the stringer technology developed by the solar panel manufacturer and the local health and safety standards for solar panel manufacturing. Common flux components include lead-free flux (Sn 100), lead-containing flux (SnPb 60/40), silver-containing flux (SnAg 96.5/3.5; SnAgCu 96.5/3.0/0.5), lead-silver flux (SnPbAg 62/36) /2), low temperature flux (BiSn 57/43, BiSnAg 57.7/42/0.3). Flux coverage thickness range is 10μm-40μm, tolerance ±10%-±30%. Commonly used flux coverage thickness is 20μm ± 4μm.

There are three methods for measuring the thickness of flux coverage. The X-ray method is an offline measurement method for single-sided thickness measurement. A manual micrometer is also an offline measurement method used to measure the total thickness of both sides of the overlay. Laser thickness measurement equipment is often used for online measurement and can be used in tinning production lines to measure the total thickness of the two sides covered during the production of PV ribbons.

PV ribbons can also be inspected visually or microscopically for the quality of the overlay and should be free of defects such as smudges, chips, dents, discoloration, bare copper visible through flux coverage, small pinholes and other mechanical defects.