Local investigation of hot spot areas on multicrystalline silicon solar cells

The formation mechanism and the electrical consequences of hot spots have been investigated in multicrystalline solar cells. The hot spots were revealed by means of an IR camera when the cells are reverse biased in the dark. The minority carrier diffusion length (L_n), the open-circuit photovoltage (V_oc) and the short-circuit photocurrent (J_sc) were measured both in the hot spot area and far from this zone by masking off and etching small mesa diodes around suspect areas. Dark forward I–V curves were plotted in order to compute the values of ideality factor (M) and reverse saturation current (J_o).It is found that J_o and M are higher in the hot spot area, while J_sc, V_oc and, to a less extent, L_n are smaller. Large densities of dislocations and lineages structures are revealed in the abnormally heated region by chemical etching of the samples. The dislocations involved in the hot spot formation could act as shunting paths for leakage currents, in addition to their contribution to recombination-generation currents.