Pressure-modulated organic-inorganic interactions in hybrid perovskites - Dr. Xujie Lü and Dr. Wenge Yang

In organic-inorganic halide perovskites, the role of organic-inorganic interactions in determining the structural and optical properties has long been underappreciated and remains unclear. Recently, an international research team led by Dr. Xujie Lü and Dr. Wenge Yang from the Center for High Pressure Science and Technology Advanced Research (HPSTAR), in collaboration with Prof. Yongping Fu from Peking University, has successfully achieved the continuous regulation of organic-inorganic interactions in the hybrid perovskite MHyPbBr₃ through pressure modulation. They discovered that compression induces strengthening of organic-inorganic interactions, resulting in an increase of structural distortion and a significant enhancement of non-linear optical properties. This innovative research, entitled "Pressure-modulated anomalous organic-inorganic interactions enhance structural distortion and second-harmonic generation in MHyPbBr₃ perovskite", has been published in the recent issue of Journal of the American Chemical Society.

Organic-inorganic hybrid perovskites have been widely used in many electronic and optoelectronic devices. "Gaining a comprehensive understanding about the influences of organic-inorganic interactions on the structural and optical properties of these materials has long been hindered. This challenge is attributed to the scarcity of suitable material systems as well as the difficulty in continuously tuning the interactions via conventional methods," said by Dr. Lü. "The distinct pressure responses of the organic and inorganic parts provide an avenue for precise and controllable manipulation of the organic-inorganic interactions through high pressure."

Caption: (a) Schematic illustration of organic-inorganic interactions in MHyPbBr₃, which includes Pb-N coordinate bonds and N-H···Br hydrogen bonds. (b) Pressure-dependent Pb-N and Pb-Br bond lengths. (c) & (d) The SHG intensity and order-disordered transition temperature of MHyPbBr₃ as a function of pressure.

By continuously regulating the organic-inorganic interactions in MHyPbBr₃ using high pressure, the researchers observed an 18-fold increase of second harmonic generation (SHG) intensity at 1.5 GPa, and the order-disorder phase transition temperature of MHyPbBr₃ increases from 408 K under ambient pressure to 454 K at 0.5 GPa. “The pronounced organic-inorganic interactions, particularly involving the Pb-N coordinate bond and N-H···Br hydrogen bond, induce distortion in the inorganic octahedron," explained by Yuhong Mao, the lead author of the study and a Ph.D. student at HPSTAR. "Through pressure modulation, these interactions are strengthened, leading to a further distorted structure of MHyPbBr₃. Consequently, this results in an enhancement of the non-linear optical properties and an increase in the stability of the distorted structure.”

This work sheds light on the intricate correlations among organic-inorganic interactions, octahedral distortion, and SHG properties and, more broadly, provides valuable insights into structural design and property optimization through cation engineering of halide perovskites.

ABX₃型有机-无机杂化钙钛矿因其优异的光电性能和良好的结构可调性，已被广泛应用于许多光电器件中，然而，这类材料中的A位有机阳离子带来的有机-无机相互作用是如何影响其结构和光电性能的，还缺乏清晰的认知。为此，北京高压科学研究中心（HPSTAR）吕旭杰研究员和杨文革研究员带领的科研团队与北京大学傅永平老师课题组合作，利用高压技术在三维卤化铅钙钛矿MHyPbBr₃ (MHy⁺ = Methylhydrazinium, CH₃NH₂NH₂⁺)中实现了有机-无机相互作用的连续调控。压力增强了有机-无机相互作用，带来了更大的无机八面体畸变，进一步使材料的非线性光学性能以及有序-无序转变温度得到显著提升。相关成果以“Pressure-modulated anomalous organic-inorganic interactions enhance structural distortion and second-harmonic generation in MHyPbBr3 perovskite”为题发表于近期的《Journal of the American Chemical Society》上。