# Low-Cost Three-Quadrant Single Solar Cell _I-V_ Tracer
## 2 Methods and Materials
### Modular Platform Used  
A modular platform was designed and used to help place the cell and the illumination LED board. The design was made using Autodesk Fusion 360 and then 3D-printed using fused filament fabrication (FFF) technology. In Figure 13, two configurations of the platform can be seen--the base with the adapters for the (156 \(\times\) 156) mm cells and the supporting rods in (a); and with the adapter for the LED illumination board used in (b). Bigger cells, up to M6--(166 \(\times\) 166) mm--are possible with this design. For future trend sizes, such as M8--(182 \(\times\) 182) mm--or M10--(210 \(\times\) 210) mm--a redesign of the platform will be needed. A picture of the prototype can be seen in Figure 14 along with the \(I\)-\(V\) tracer device.  
Figure 14: Modular platform mounted in the \(I\)-\(V\) tracer mode. (**a**) Assembled except for the LED board. (**b**) Fully assembled with the LED board in place.  
Figure 13: Modular platform designed for the measurement of \(I\)-\(V\) curves, electroluminescence, thermography, and other techniques. (**a**) Base with the cell and adapters. (**b**) With the Radon for supporting the LED illumination board.  
PV cells and LED illumination.  
The characteristics of the PV cells used for testing are in Table 1. Busbars were hand-soldered to the cells using a soldering iron with the help of flux and hot air at 150 \({}^{\circ}\)C (see Figure 15a). The four busbars were then connected using a wider bar, which offered a low resistance path for the current and an easy zone to solder the voltage and current cables. Three cables were soldered at different points of each side (positive and negative) from the cell to the device to ensure the current flow with the lowest resistance possible. Another cable was soldered on each side for the voltage measurement.  
The illumination system was composed of an aluminium PCB with 42 infrared (IR, 850 nm) LEDs--see Figure 15b. This wavelength was chosen because the photon absorption curve for a silicon PV cell had its maximum efficiency in the near-infrared (NIR) zone, as shown in Figure 16. When these photons illuminating the cell are at their peak wavelengths, they could absorb better, so less energy is needed to obtain a state at the cell similar to the nominal conditions (1000 W/m\({}^{2}\) with the spectral composition of the Sun's irradiance at Earth's surface). Under these irradiation conditions, the PV cell can generate the free charges needed to reach its saturation current and, consequently, walk around its own \(I\)-\(V\) curve. The calibration of the current needed on the LEDs for obtaining the right density of photons was conducted with a calibrated irradiation cell to obtain the same signal exposed to the Sun at nominal conditions.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Characteristic** & **Value** \\ \hline Max power (MPP) & 4.67 W \\ \(V_{\text{OC}}\) & 0.645 V \\ \(I_{\text{SC}}\) & 8.99 A \\ \(F\) & 0.81 \\ Efficiency & 19\% \\ Number of busbars & 4 \\ Size & (156 \(\times\) 156) mm \\ Thickness & 200 \(\upmu\)m \\ Technology & Polycrystalline \\ \hline \hline \end{tabular}
\end{table}
Table 1: Technical characteristics of the PV cells used at nominal conditions (1000 W/m\({}^{2}\) of solar spectrum and 25 \({}^{\circ}\)C).  
Figure 15: **(a)** Photovoltaic cell used. **(b)** LED illumination system used.