# Cell/Module Integration Technology with Wire-Embedded EVA Sheet
## 3 Results  
It is essential to design the structure of the module before fabricating the wire-embedded EVA sheet module using the cell/module integrated process. Variables such as the number and spacing of wires interconnected with the finger electrode of the busbarless cell serve as important factors in determining the output of the module. In this study, the front electrode of the wire-embedded EVA sheet module was designed using various simulations such as Griddler 2.5 and MathCAD, and the influence of various variables such as the number of wires and wire diameters on the module power was analyzed. Cell parameters were applied based on a PERC-structured c-Si solar cell. For the parameters of the simulation, the size of the wafer was 156.75 \(\times\) 156.75 mm\({}^{2}\), the thickness of the wafer after texturing was approximately 170 \(\upmu\)m, and the sheet resistance after the formation  
Figure 1: Wire-embedded EVA sheet module process flow. of the emitter was approximately 120 ohm/sq. At this time, the finger line width of the front electrode was fixed at 30 \(\upmu\)m, and the number of fingers was set to 90. The optimum line width and efficiency values were derived based on the number of busbars in the front electrode. Figure 2 compares the measured values and the simulated values of module characteristics and the efficiency value based on the number of busbars with a line width of 0.26 mm. The efficiency increased as the number of busbars increased and decreased when the number of busbars was 38. As the number of busbars increases, the shading loss increases owing to the busbar area, which leads to optical loss, resulting in a decrease in efficiency. The module for this analysis was manufactured using a low-melting-point solder-coated wire with a line width of 0.26 mm, and the module was manufactured using one solar cell. The 1 \(\times\) 1 unit module was manufactured based on the number of wires of 6, 12, 18, and 24 wires; a difference occurred between the simulation value and the actual efficiency measurement value. A wire-type busbar was used for contact with the finger line when a module was manufactured using a busbarless cell. Accordingly, the contact area and losses were different from those of the conventional busbar-type electrode. When a wire is applied, light reflection occurs on the curved surface of the wire, reducing the effective light-transmitting area of the busbar, which leads to a reduction in shading loss, which is a light loss owing to the busbar. It is necessary to perform a simulation of the front electrode based on the changed measurement conditions. The above simulation result using Griddler 2.5 is the value derived by setting the effective shading area of the busbar to a value of 100%. For a wire, part of the light is incident on the surface of the solar cell owing to the curved surface, and another part of the light is reflected; further, the reflected light is directly incident on the surface. Another part of the reflected light after encapsulation is reflected at the interface between the module glass and air and is then incident on the surface of the solar cell. Accordingly, the contact area between the finger line and wire is different because of the curved surface of the wire shape. The difference between the simulated and actual measured values occurred because the effective light transmission area ratio was different. The simulation program should derive the result by considering the contact area between the wires and the finger line. Figure 3 shows the schematic of the conventional rectangle-type busbar and wires. Based on literature research [21], it was confirmed that the effective shading area was observed differently by the light incident on the wire. For a wire, the incident light is directly reflected on the cell surface, and the effective shading area is reduced to approximately  
Figure 2: Simulated values and measured values based on the number of busbars for c-Si solar cell. 70% of the actual area.