Full analysis of series resistance components and their degradation in temperature cycling of PERC solar cells

Abstract

Accelerated aging of solar modules using temperature cycling is an international standardized part of the qualification procedure of solar modules. This procedure is applied to passivated emitter and rear contact solar cells, modules and test structures in this work. A breakdown of all series resistance contributions of the metallization and interconnection during the observed degradation of PERC solar cells under test, shows an increase in lumped series resistance. By using 3D FEM simulation, we combine the individual resistance values with their interaction on module level and therefore their effective series resistance effect during degradation. The main driver of the serial resistance degradation of multicrystalline PERC cells is to the loss of pressure contact and increase of aluminum sheet resistance and solder contact resistance. The pressure contact between interconnection ribbon and cell metallization on front and rear degrades fast during thermal cycling, resulting in a sudden rise of the series resistance of 0.1 Ωcm2 after 50 cycles, ending in 0.15 Ωcm2 after 400 cycles. Whereas the continuous degradation of aluminum rear metallization and solder contact leading to a 0.07 Ωcm2 and 0.18 Ωcm2 increase in series resistance, respectively. The overall series resistance increases of 0.45 Ωcm2 is in good accordance with the degradation of 1-cell modules and therefore proves the detailed characterization of each series resistance contribution. Thus, it is exemplarily shown in detailed temperature cycling investigations which solar cell components are affected during thermal cycling, what is typically not accessible during solar module reliability testing.