LBIC investigations of the lifetime degradation by extended defects in multicrystalline solar silicon

A calibrated measurement of the short circuit current and the surface reflection coefficient can be directly converted into the internal quantum efficiency (IQE) of a solar cell. The IQE at a wavelength of 833 nm were measured on ingot, EFG and RGS silicon solar cells with a spatial resolution of 6 mu m. ingot solar cells were found to be predominantly influenced by a homogeneous distribution of recombination centers. However, if the dislocation densities exceeded a certain limit the IQE was reduced by recombination at dislocations. This limit varied in different parts of the wafer. EFG solar cells only showed a lifetime reduction by dislocations whereas the investigated solar cells made of RGS silicon were dominated by recombination at grain boundaries. The RGS silicon was further investigated by TEM- measurements, which showed that the extended defects were highly decorated with SiO2- and SiC-precipitates.