In this work, time dependent changes of the open-circuit voltage and the doping density of the absorber under red-light illumination of Cu(In,Ga)Se2 solar cells are investigated. The experimental results show that the open-circuit voltage is linear on a logarithmic time scale under red-light illumination at room temperature and that the doping density increases according to a power law. From this it can be concluded that solar cells with increasing open-circuit voltage under red light are dominated by volume recombination, whereas solar cells with decreasing open-circuit voltage under red light are dominated by interface recombination (CdS/CIGSe). The combination of both time dependent measurements shows that changes in the open-circuit voltage are induced by changes in the doping density, which means that changes of recombination-active defects, in general, can be excluded. To compare the time dependent measurements with established theoretical models, time dependent solutions of copper migration as well as of the Lany-Zunger model are introduced. The interpretation of the experimental findings leads to the elimination of the copper-migration model, because the expected changes by copper migration during the experimental time scales, especially at lower temperatures, are too low. Also the Lany-Zunger model including only the metastable (VSe −VCu) defect complex is not able to explain the experimental findings. Assuming metastable defects with different metastable properties, e.g. transition rates, energy barriers or defect densities, the Lany-Zunger model is generalized. Using this, all experimental findings can be understood.