The invention relates to a method for producing a radiation detector used to detect ionizing radiation including a first inorganic-organic halide Perovskite material (24) as a direct converter material and/or as a scintillator material in a detector layer and to a radiation detector comprising a detector layer (24) produced by means of the steps of the method. In order to provide an approach for producing a thick layer (e.g. above 10 μιη) of Perovskite material suitable for a radiation detector, it is proposed to grow the material selectively on a seeding layer (23), yielding in a thick polycrystalline layer. One suitable seeding layer (23) to grow lead Perovskite material is made of a bromide Perovskite material.