Reverse bias degradation of metal wrap through silicon solar cells

The study of solar cells subjected to reverse biasing is of fundamental importance since the reliability of an entire solar panel can be influenced by the presence of leakage paths on a single solar cell. The particular situation of reverse biasing can occur when, in a module, a solar cell is shadowed and the illuminated solar cells force the generated current through the shadowed solar cell that is reverse biased. The situation is further aggravated by the fact that reverse current crowds in localized shunt paths ("hot spots") that are related to the presence of semiconductor defects. In this biasing condition the shadowed solar cell acts as a load and it can dissipate tens of watts with the risk of high temperature and damaging of the encapsulating materials. In this paper we study the effects of reverse biasing on metal wrap through (MWT) solar cells. This cell structure is particularly sensitive to reverse-bias, due to the presence of via holes in the junction. The presence of "hot spots" can be related to the through hole metallization pattern: this leads to the conclusion that the MWT production process may strongly affect the reliability of this technology and should be optimized to avoid the formation of parasitic reverse current paths in the crystal structure.