Effect of Shunt Resistance on the Performance of mc-Silicon Solar Cells: A Combined Electro-Optical and Thermal Investigation

In this paper we discuss the effect of shunt resistance on the electro-optical characteristics of multicrystalline silicon (mc-Si) solar cells at different illumination levels. The analysis is based on combined electro-optical characterization and thermographic measurements of solar cells with similar efficiencies, but with different shunt resistance levels. In order to understand how the shunt resistance can affect the performance of mc-Si solar cells, a special setup for J-V characterization at several illumination levels was developed. Results indicate that (i) a low shunt resistance is strongly correlated to the presence of hot spots, which can be identified by means of infrared thermography; (ii) solar cells with different shunt resistance levels can show significantly different fill factors and efficiencies, particularly at low irradiation levels. This can strongly influence the reliability of modules at low illumination conditions; (iii) the electrical characteristics of mc-Si solar cells can be modeled with good results, by considering the equivalent two-diode electrical model and solving it by a circuit simulator like SPICE.