The efficiency of multi crystalline silicon solar cells is around 17% but the theoretical limit is 33,7 %. Impurities and dislocations are the main sources for degradation of the solar cell efficiency, especially the combination. Dislocations are also responsible for plastic deformation of materials. To improve the solar cell efficiency it is important to reduce the dislocation density in the raw material for solar cells. The nucleation and multiplication of dislocations in wafer can be suppressed by doping it with a method called solid solute strengthening. In solar cells, the minority carrier lifetime, internal quantum efficiency and the solar cell efficiency are also affected by germanium despite although it is, electrically inactive in the silicon lattice. In this thesis I have studied how all these factors are affected by germanium with different experimental methods. The main goal is to conclude if germanium could be a cost effective dopant in future solar cell production.