At present, the Czochralski method is the standard procedure for making monocrystalline ingots. With our Czochralski machine, we are able to pull crystals of industrial dimension with typical diameters of 8'' (210 mm). Current challenges are the provision of n-type material with as little variation in resistance as possible, as the basis for highly efficient cell concepts. At the Fraunhofer CSP's Laboratory for Crystallization Technology (CSP-LCT) in Halle we study the incorporation behavior of various doping substances and test several different ways to influence the profile of axial resistance. One approach we are now working on consists in the additional doping with gallium. Another possibility consists in the subsequent introduction of silicon into the process.