High-throughput exploration of Sn-based halide perovskites for photovoltaic applications

Global energy consumption continues to rise annually, making the decarbonization of energy sources an urgent necessity to mitigate global warming. Advances in data-driven material discovery have become a key focus for meeting the demands of specific energy applications. This thesis presents an experimental workflow combining combinatorial synthesis and high-throughput characterization to opti- mize the fundamental properties of perovskite semiconductors for photovoltaic applications. The chemical space of tin (Sn) and mixed tin-lead (Sn-Pb) perovskites is explored by depositing compositional gradients by thermal co-evaporation. Par- ticularly for Sn-based perovskites, which are prone to rapid crystallization and oxidation during solution processing, thermal co-evaporation offers the advan- tages of suppressing oxidation and providing precise thickness control. Automated high-throughput optical characterization techniques are employed to investigate optoelectronic properties, where optical absorption, photoluminescence, electrical conductivity and lifetime of charge carriers are the major experimentally acquired data. Three approaches on compositional tuning are demonstrated in this the- sis. First, the A- and B-site cation concentrations are varied during deposition of CsSnI3. Using X-ray-based techniques, the formation of the perovskite phase with the Sn2+ oxidation state is confirmed. A significant impact of cation con- tent on phase transitions is established under different atmospheric conditions. Further optoelectronic analysis reveals that compared to excess Cs compositions, the Sn-rich side exhibits decreased electrical conductivity, reduced doping den- sity and low photoluminescence intensity, attributed to the suppression of Sn vacancy defects by excess Sn. A distinct blue shift observed in the absorption onset of the Cs-rich perovskites is identified as the Burstein-Moss effect. This experimental study demonstrates a correlation between cation substitution and both the phase stability and the optoelectronic properties of perovskites. Second, CsSn(I1-xBrx)3 combinatorial library with Br contents up to 33% is investigated using high-throughput characterization to study the effect of halide ratio on sta- bility and optical properties. Analysis of the steady-state and transient PL measurements indicates the influence of Br addition on charge carrier density, leading to variations in optical band gap energies. Finally, the impact of the B-site cation on the optoelectronic properties of CsSnxPb1-x(I0.87Br0.13)3 is characterized using high-throughput optical screening. The influence of Sn content on charge carrier dynamics is confirmed and the photovoltaic parameters are predicted based on the optoelectronic results. Overall, this thesis analyzes 7935 chemical compositions and demonstrates strategies to optimize phase stability and optical properties in all-inorganic Sn- and Pb-based perovskites.