Understanding Dimensionality and Connectivity of Mixed-Cation Hybrid Perovskites

Student’s name: Monique Kubovsky Home Institution: University of Florida NNCI Site: RTNN @ Duke University REU Principal Investigator: Dr. David B. Mitzi - Department of Chemistry and Department of Mechanical Engineering and Materials Science, Duke University REU Mentor: Migon Choi - Department of Mechanical Engineering and Materials Science, Duke University Abstract: Perovskites are being increasingly studied due to their promising applications in solar cells, LEDs, and photodetectors; low-dimensional hybrid perovskites, in particular, exhibit fluorescence and exciton effects, as well as low defect densities. Introducing large cation spacers between the inorganic layers in low-dimensional perovskites plays a pivotal role in determining dimensionality by affecting the degree of connectivity and distortion, influencing bond angles and lengths. Being able to manipulate the dimension and connectivity of perovskites allows for the tuning of the material’s properties, aiding in their applications to electronics. Despite the organic cation spacer’s importance, there has been limited attention given to investigating how mixing the organic spacers will impact perovskite structure. In this study, we aim to understand the nature of dimensionality and connectivity within hybrid halide perovskites with mixed organic cations. We chose to mix branched aliphatic cations, that were known to yield one-dimensional face-sharing and one-dimensional corner-sharing structures depending on the cation to lead iodide ratio, to understand if the resulting phases would be altered. The slow evaporation method was used for synthesizing single crystal perovskites with mixed cations, followed by powder x-ray diffraction and single crystal x-ray diffraction to determine the dimension and connectivity the crystals yielded. We observed that the cation that is more favorable than the other to crystalize with the inorganic precursor tends to crystalize first, determining the crystal’s dimension and connectivity. However, when the two cations have similar tendencies to crystalize, we may see cation mixing within the crystals, suggesting that new structures, different from the pure cation structures, can be synthesized. This study allows us to better understand the impact on the structure choice of dimension and connectivity that organic cations produce in metal-halide perovskites. More informed control of low-dimensional perovskite structures will lead to property tunability of low-dimensional perovskites.