PV Ribbon (PV Busbar & Tabbing wires) knowledge comprehensive summary

General Introduction

As the manufacturing level of PV module industry is continuously improving, each module enterprise wants to pursue higher quality products. First of all, high quality raw material squares should be selected to ensure the quality of the modules. And there are only three aspects that really have a key impact on the intrinsic quality of the modules. First, the battery, second, the PV ribbon, and third, the junction box. Because they have a close relationship with the output power of the module directly.

The choice of PV ribbon is more critical. Although the share of the module is only about 0.8 percent. But the role it plays is huge.

The PV ribbon is welded to the positive main grid and the negative main grid of the adjacent cell. The positive and negative terminals of the two cells are connected to form a string. Multiple cell strings are then connected in parallel to form a photovoltaic module through the converging welding tape.

Tabbing wire is an important raw material in the process of PV module welding. the quality of PV ribbon will directly affect the efficiency of PV module’s current collection. It has a great impact on the power of the PV module. PV ribbon (tabbing wire) width should be consistent with the width of the main deletion line of the battery, the softness and hardness of PV ribbon generally depend on the thickness of the cell and welding tools.

In the solar module production process, the electrode (current) of the cell is exported through the welding process, and then the leaded electrode is effectively connected to the junction box through a series or parallel connection. Therefore, PV welding tape is further divided into two types: PV tabbing wire and PV busbar tape.

I. Function

PV ribbon plays the role of connection and sinks in the module production process. The current from the cell is derived through the welding process. Then the leaded electrodes are effectively connected to the junction box through a series or parallel connection. Therefore, PV welding strips are further divided into two types: PV tabbing wire and PV busbar.

PV tabbing wire is welded on the front and back side of the cell, which will lead to the current collected by the cell. At the same time, the thickness should not be so thick that it will cause the cell to collapse during the lamination stage.

During the module reproduction process, cells are connected in series in a certain number. The PV busbar is selected to minimize power loss. This requires it to have a certain width to reduce its own resistance.

II. Composition

PV ribbon is generally composed of two parts: copper base material and surface coating.
The PV ribbon is mainly distinguished by the composition of the surface coating.

2.1 Copper base material

PV ribbon in the process of use, the role of backbone conductive is copper. The higher the purity of copper, the lower the resistivity, the greater the load-bearing capacity and the better the plasticity. The copper base material of PV ribbon is generally high purity oxygen-free copper. Oxygen-free copper is pure copper that does not contain oxygen or any deoxidizing

Oxygen-free copper is pure copper without oxygen or any deoxidant residues. However, it actually contains very small amounts of oxygen and some impurities. According to the standard, the content of oxygen is not more than 0.03%, the total content of impurities is not more than 0.05%, and the purity of copper is more than 99.95%.

According to the oxygen content and impurity content, oxygen-free copper is divided into No. 1 and No. 2 oxygen-free copper. The purity of No.1 oxygen-free copper reaches 99.97%, the oxygen content is no more than 0.003%, and the total impurity content is no more than 0.03%. No. 2 oxygen-free copper purity of 99.95%, the oxygen content of not more than 0.003%, the total content of impurities is not more than 0.05%.

PV ribbon’s copper is No.2 oxygen-free copper with a purity of more than 99.99%.

2.2 Coating

Although its main conductive role is the copper substrate, the importance of the PV ribbon surface coating is not to be ignored. PV ribbon is distinguished by the composition of the coating and its content.

Coating compositions generally include the following types:

SnPb: 60/40; 63/37 (183°C)

SnPbAg: 62/36/2 (178°C)

SnAg: 96.5/3.5 (221°C)

SnAgCu:96.5/3.0/0.5 (217-220 ℃)

Sn100: Pure Tin (232 ℃)

Among them, the role of silver (Ag) is to improve the mechanical strength of PV ribbon and improve the thermal fatigue strength in the case of lead-free. Silver is less ductile, less processable and more costly than lead. The role of copper (Cu) is to improve the wettability of the solder and improve the thermal fatigue strength, this copper is not the copper used in the copper base material.

The most commonly used coating composition is tin-lead coating. There are 63,37 coating and 60,40 coating. For one thing, the cost is lower, and it is easy to use and more effective. However, since lead has some toxicity, it should be used with care and protection.

III. Important parameters

◆Copper base: oxygen-free copper / T2 purple copper, copper content ≥ 99.99%, conductivity ≥ 98%

◆Resistivity of the copper base: oxygen-free copper ≤ 0.0165Ωm㎡/m T2 purple copper ≤ 0.0172Ωm㎡/m

◆Coating composition: 63%Sn37%Pb

◆The coating thickness: single-sided coating 0.01~0.05mm, uniform coating, bright and smooth surface.

◆Coating melting point: 183℃

◆Tensile strength: soft state ≥ 25kgf/m㎡ semi-soft state ≥ 30kgf/m㎡

◆Elongation of welded tape: soft state ≥ 30% semi-soft state ≥ 25%

◆Width error：±0.1mm

◆Thickness error: interconnection belt ±0.01mm, convergence belt ±0.015mm.