A novel structure assembly strategy by introducing flexible carboxylic acid amine motifs

The spontaneous polarization of ferroelectric semiconductors interacts with photo-generated carriers, which has produced physical properties with important application prospects and has become a powerful candidate material for the development of new optoelectronic devices. In recent years, two-dimensional RP-type perovskite has emerged in this field. However, adjacent organic ion layers in its crystal structure are connected by weak van der Waals interaction, which is not conducive to maintaining the stability of its own structure. Under the premise of realizing RP-type lattice ferroelectricity, how to eliminate or reduce the interlayer energy gap and enhance the structural stability is a challenging topic in this direction.

On the basis of the previous work, Luo Junhua’s team, a researcher at the State Key Laboratory of Structural Chemistry "Inorganic Optoelectronic Functional Crystal Materials", Fujian Institute of the Structure of Matter, Chinese Academy of Sciences, proposed a novel structure assembly strategy, by introducing flexible carboxylic amine motifs and using hydrogen The bond acts to eliminate/reduce the energy gap in the crystal structure, thereby enhancing the structural stability of the ferroelectric compound. The results show that there is a strong O-H···O hydrogen bonding force between the carboxylates of the isomorphic trans isomer, which connects adjacent organic cation layers and effectively reduces the energy gap between the layers. The grid stability has been significantly improved. At the same time, the order-disorder transition of the carboxylic acid amine element induces a symmetry-breaking structural phase transition, which plays an important role in the generation of spontaneous polarization. The temperature-variable single-crystal structure analysis, nonlinear optics, and electrical properties have confirmed the material Ferroelectric effect.

Elimination of hydrogen bonding/reduction of van der Waals energy gap to construct a novel hybrid optical ferroelectric semiconductor

Based on the two-dimensional RP-type perovskite framework, this compound has strong structural anisotropy and spontaneous in-plane polarization effects. Under polarized light irradiation, it exhibits bulk photovoltaic characteristics that depend on ferroelectricity, and the intrinsic dichroic ratio of the material reaches ~3.2, which is better than most traditional inorganic two-dimensional material systems. This research is the first to design two-dimensional RP-type ferroelectrics using the structural elements of isomorphic and trans-isomers. The strategy of eliminating/reducing the van der Waals energy gap through hydrogen bonding provides an important reference for the design and synthesis of novel ferroelectric materials.

Relevant research results were published in "Journal of the American Chemical Society" (J. Am. Chem. Soc. 2021, 143, 4, 2130-2137). Researcher Sun Zhihua is the corresponding author of the paper, and Liu Yi, a doctoral student at the University of Chinese Academy of Sciences, is the first author of the paper. The research work was funded by the National Natural Science Foundation of China, the Basic Frontier 0-1 Original Innovation Project of the Chinese Academy of Sciences, and the Strategic Leading Technology Special Project of the Chinese Academy of Sciences.