Design, synthesis, and characterization of organic inorganic Halide Perovskite single crystals

Halide perovskites have gained attention for their potential in electronic applications such as photovoltaic cells, photodetectors, LEDs, and sensors due to their unique properties such as high-power conversion efficiency, adjustable bandgap, cost efficient solution processed fabrication, and high absorption coefficient. A new class of organic inorganic hybrid halide perovskites has been reported to demonstrate significant piezo-/ferroelectricity, yielding novel multifunctionality, including energy conversion and storage. Hybrid halide perovskites have shown great promise due to their straightforward and cost-efficient synthesis, as well as their mechanical flexibility making them promising alternative to inorganic counterparts. Significant progress has been made in the design and development of novel hybrid halide perovskites piezo/ferroelectrics. Of particular interest is TMCM-CdCl3 (TMCM = trimethylchloromethyl ammonium), which was reported to show a large piezoelectric coefficient (d33) and a saturation polarization (Ps) and a relatively high TC. Even though many studies have been dedicated to the fundamental properties of halide perovskites, there are still some challenges that need to be addressed, such as the understanding of domain structures, phase transitions, mechanisms of piezo/ferroelectricity, and the improvement of piezo/ferroelectric response to meet the advanced demands of electromechanical applications. The research described in this thesis, focuses on design and synthesis of novel piezo-/ferroelectric and ferroelastic materials, while also establishing the structure-property relationships of organic-inorganic hybrid halide perovskites. One of the challenges encountered in this project centres on the absence of a definitive design principle for developing novel, high-performance piezoelectric halide perovskites. In this research, we followed a theoretical design approach called the 'quasi-spherical theory' for the synthesis of novel hybrid halide perovskites and evaluated the efficiency and applicability of this approach. Through this objective, we successfully grew a few promising hybrid halide single crystals, including TMCM-CdCl3, the new DMECM-CdCl3 (DMECM = dimethylethylchloromethyl ammonium chloride) and (QCM)2CdCl4 (QCM = quinuclidinechloromethyl ammonium chloride). These new compounds exhibit different dimensionalities: DMECM-CdCl3 is a 1D organic-inorganic halide perovskite, while (QCM)2CdCl4 is a 0D organic metal halide. Furthermore, the structure-property correlations in organic-inorganic hybrid halide perovskites, such as the correlation between structural phase transitions, piezo/ferroelectric properties, and dielectric properties, are established. This provides an ideal platform for gaining insights into the intrinsic properties that have not been thoroughly understood yet.