Structure-Property Control for Enhanced Spin-Related, Optical, and Thermal Properties of Layered Halide-Based Hybrid Perovskites

Abstract

Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) present remarkable prospects for advancing emergent optoelectronic and spin-related technologies, primarily due to their tunable structural symmetry-breaking and distortions. The deviation of metal and halogen atoms from symmetric positions within the inorganic lattice is primarily influenced by the steric effects of organic cations through the complex organic-inorganic hydrogen (H) bonding interactions. This tunable structural asymmetry is aided by modifying molecular configurations, including adjustments to the location of chiral moieties, aryl-ring substituent composition and placement, polycyclic aromatic hydrocarbon size, and alkyl chain length. Despite increasing efforts to enhance structural asymmetry, the resulting structural properties and associated key property parameters, such as spin splitting and spin lifetime, have yet to reach ideal levels. Strong spin splitting facilitates the efficient control and manipulation of electron spins, which is essential for the development of advanced spintronic devices. The scarcity of asymmetric 2D HOIP systems constrains a thorough exploration of the structure-properties correlation, thereby impeding the efficient screening and discovery of candidate 2D HOIP materials for spintronic applications. To address these challenges, the following studies are conducted: 1. Development of new material design strategies aimed at enhancing the templating effect and achieving desired structural properties. Additionally, utilization of temperature as an environmental stimulus to induce asymmetric structural transitions in 2D HOIPs; 2. Investigating optical, spin-related, and thermal properties for the new materials; 3. Quantitively understand the structural properties and establish a deeper and comprehensive correlation between structure and property. After an extensive exploration of new 2D HOIPs and a thorough investigation into the acquired structures and their influence on the associated emergent properties, the following conclusions are drawn: 1. Cation mixing emerges as a promising avenue for diversifying 2D HOIP structures and modulating structural symmetry. Various innovative cation mixing paradigms, including chiral cation doping and mono- and heterochiral mixing, have been demonstrated. Their effects on structural symmetry can manifest in two ways: a. Elimination of symmetry elements and modulation of the structure to the lowest symmetry state (P1); b. Amplification of asymmetric distortions. 2. The thermally-induced structural transition can break inversion symmetry and induce a larger degree of structural asymmetry. Additionally, the structural transitions in 2D HOIPs can be controlled by employing kinetic effect. 3. The enhanced structural asymmetry obtained as part of the current studies induces a more significant spin splitting and exhibits an impact on chiroptical properties. Pioneering material design strategies, complemented by structural transitions driven by environmental stimuli, can serve as a systematic scheme to optimize structural and associated properties. 4. To understand the mechanism of the organic templating effect and structural symmetry breaking, we not only precisely characterize the H-atom positions and H-bonding parameters using neutron diffraction, but also propose a more accessible DFT-based approach to help wider people to obtain neutron-quality results based on the quicker/less-expensive X-ray data. 5. We introduced a mathematic approach to continuously quantify the symmetry breaking in 2D perovskites and establish a quantitative correlation between symmetry breaking, distortion parameter, and spin-related properties.