In the past ten years, Halide Perovskites gained enormous attention due to the rapidly increasing performance
of Perovskite Solar Cells (PSCs). Starting with firstly reported power conversion efficiencies of
3.8% in 2009 researchers now present groundbreaking results of 23.7%[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 what the best composition is and why the observed
differences in performance and stability are present[4]. To affect the crystal structure and therefore the
perovskite properties doping is used. Structural knowledge of doped 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 absorption measurements (EXAFS) supported by x-ray fluorescence (XRF) and
small angle x-ray scattering (SAXS) to enhance the structural understanding of the perovskite formation.
As already a higher performance for doped PSCs was achieved, in our work we want to analyse the reason
for the observed behaviour. Hence, we concentrate on a strontium (Sr) doped perovskite system (MAPbI3).
To further investigate the chemical composition the L3-edge of iodine is measured using synchrotron radiation
at BessyII. Two compounds with different doping concentrations are compared to the undoped perovskite.
The results indicate possible ways how to explain the observed different behaviour of the systems.
Furthermore, we aim to detect and quantify the small amount of strontium in the perovskite film. For this
purpose, we performed XRF on the perovskite surface, which provides important information on how the
strontium is distributed and how it is interacting with the perovskite film. Supporting information about the
grain size distribution and crystal growth is given by SAXS and ASAXS (Iodine) measurements.
Via EXAFS, SAXS/ASAXS and XRF an enhanced image of the coordination chemistry in thin film perovskite
can be obtained, which may lead to a controlled adjustment of the processing of stable perovskites.
Thus, aim of the study is using the derived information to enhance the long-term stability of PSCs.