In the past ten years, Halide Perovskites gained enormous attention due to the rapidly increasing performance of perovskite solar cells. Starting with firstly reported power conversion efficiencies of 3.8% in 2009 researchers now present groundbreaking results of 24.2%[1]. Driven by their fascinating properties, such as long charge carrier diffusion length and large absorption coefficients, halide perovskites became one of the most interesting materials for photovoltaic applications[2], [3]. Based on the general ABX3 structure of perovskites, where the A-side cation is commonly occupied by methylammonium (MA), formamidinium (FA) or cesium (Cs), the B side cation by lead (Pb) or tin (Sn) and the X side anion by halide anions such as iodine or bromine, many different compositions exist showing varying degrees of the above described features. Still, it is not determined why the observed differences are present. One approach to give an explanation might lay in a deeper knowledge of perovskites structural properties. 

Structural modifications induced by adding small amounts of specific elements lead to an adjustment of the electronic structure and properties of perovskites. A deeper knowledge of these doped perovskite systems compared to undoped perovskites may lead to a better understanding of crystal formation and further to control the properties of different perovskite compositions. In our work, we focus on the characterization of methylammonium lead iodide perovskite (MAPbI3) compared to a strontium (Sr) doped perovskite system (MAPbI3).  Using X-Ray Fluorescence Spectroscopy, we are able to identify even small amounts (0.2 at%) of strontium in the perovskite thin films. Moreover, in this work, we propose the use of resonant elastic X-ray spectroscopy such as anomolous small angle X-ray scattering (ASAXS) as a comprehensive methodology to obtain a more detailed characterization of halide perovskites using synchrotron radiation at BESSYII. ASAXS provides valuable information about the crystal growth and grain size distribution in the perovskites thin films. In addition to measuring the thin films, we also performed SAXS experiments on the precursor solutions corresponding to the thin films. First results confirm a cluste  r formation starting already in the liquid precursor phase. Interestingly, different features are observed for each investigated perovskite system, which in the end also leads to differences in the perovskite film and stability of the perovskites. A combination of the results from spectroscopy with full device perovskite solar cell performance may lead to a controlled adjustment of the processing of stable perovskites.