Analysis of the dynamic time response of a solar element or other photovoltaic devices after a pulse illumination gives more details of microphysical processes and inherent parameters. By means of different types of investigations one can separate diffusion and lifetime effects. Using different wavelength of irradiation, the influence of back side contact effects is to analyze with respect to the optical and recombination properties. Because the capacitance of the depletion layer and the concentration of acceptors is included into the registrated voltage decay, both parameters can also be determined. Measurements were made by using excimer laser radiation of 308 nm wavelength and 10 ns duration or dye laser radiation within a spectral range from 500 nm to 700 nm. The available radiation flux density was in a range from 10 mW/cm2 to 100 W/cm2. The irradiation was applied at front or rear side of commercial solar cells. Mono and poly crystalline material were investigated. The transient responses in short circuit current and open circuit voltage was registrated with a high speed DSO. For analyzing the physical processes, a numerical simulation of the cell has been developed. This modeling allows to study the fundamental effects and their time evolution step by step. Values for different parameters can be obtained by a mathematical fitting procedure. The results of various samples will be shown and discussed.