Since the last years hybrid perovskite materials became attractive in photovoltaic applications. They offer a broad range of properties, for instants a tunable wide-bandgap which is directly related to their chemical composition. Investigations on MAPbI3-xBrx solid solution thin films promise bandgaps between 1.77 and 2.05 eV. Less focus has been set on structural details of this material. X-ray powder diffraction studies at different temperatures revealed interesting phase transition behavior. By Rietveld refinement of the XRD-data the structural parameters can be determined to gain the phase diagram of the composition.