Shunt types in multicrystalline solar cells

Nine different types of shunts have been found in state of the art multicrystalline solar cells by lock-in thermography and identified by SEM-investigation (incl. EBIC), TEM and EDX. These shunts differ by the type of their I-V characteristic (linear or non-linear) and by their physical origin. Six shunt types are process-induced, and three are caused by grown-in defects of the material. The most important process-induced shunts are residues of the emitter at the edge of the cells, cracks, recombination sites at the cell edge, Schottky type shunts below grid lines, scratches, and aluminum particles at the surface. The material-induced shunts are strong recombination sites at grown-in defects (e.g. metal-decorated small-angle grain boundaries), grown-in macroscopic SiN inclusions, and inversion layers crossing the wafer (e.g. carbon-induced).