Abnormal Phase Transition and Band Renormalization of Guanidinium-Based Organic–Inorganic Hybrid Perovskite

Abstract

Low-dimensional organic–inorganic hybrid perovskites have attracted much interest owing to their superior solar conversion performance, environmental stability, and excitonic properties compared to their three-dimensional (3D) counterparts. Among reduced-dimensional perovskites, guanidinium-based perovskites crystallize in layered one-dimensional (1D) and two-dimensional (2D). Here, our studies demonstrate how the dimensionality of the hybrid perovskite influences the chemical and physical properties under different pressures (i.e., bond distance, angle, vdW distance). Comprehensive studies show that 1D GuaPbI3 does not undergo a phase transition even up to high pressures (∼13 GPa) and its band gap monotonically reduces with pressure. In contrast, 2D Gua2PbI4 exhibits an early phase transition at 5.5 GPa and its band gap follow nonmonotonic pressure response associated with phase transition as well as other bond angle changes. Computational simulations reveal that the phase transition is related to the structural deformation and rotation of PbI6 octahedra in 2D Gua2PbI4 owing to a larger degree of freedom of deformation. The soft lattice allows them to uptake large pressures, which renders structural phase transitions possible. Overall the results offer the first insights into how layered perovskites with different dimensionality respond to structural changes driven by pressure.

Spacer-Dependent and Pressure-Tuned Structures and Optoelectronic Properties of 2D Hybrid Halide Perovskites

“…The mechanical compression of perovskites can result in modification of the Pb–X bond lengths and angles in the inorganic lattice. The subsequent change in orbital overlap results in modification of the observed optoelectronic properties. − The effects of high pressure on 3D HOIPs, such as MAPbI 3 and FAPbI 3 , have been studied extensively. − More recently, high-pressure studies have been conducted on 2D lead-halide-based HOIPs, mostly focused on those with BA (butylammonium), PMA (phenyl methylammonium), or PEA (phenyl ethylammonium) spacer cations. − However, the effects of different spacer cations on the pressure-tuned optoelectronic properties are still not well understood. For example, the PMA and PEA spacer cations differ only by a CH 2 group, yet the high-pressure behaviors of (PMA) 2 PbI 4 and (PEA) 2 PbI 4 are drastically different.…”

“…In particular, the interplay between organic and inorganic layers in other 2D HOIPs with rigid spacers suggests that the distortion and tilting of the PbI 6 significantly influence the evolution of bandgap energies under high pressure, including the nonmonotonic fluctuation and/or direct-to-indirect transition in bandgaps. ,, The computationally optimized crystal structures of CMA 2 PbI 4 at different pressures, however, suggest that no significant changes occur in bond angles in either the PbI 6 octahedra or the Pb–I–Pb angle between adjacent octahedra, which maintains at approximately 152° upon compression and decompression in the entire pressure region and indicates no significant tilting of the PbI 6 octahedra. The major changes were found to be in the Pb–I bond lengths (Figure S8b) with anisotropic pressure-induced contraction ratios, which leads to some degree of individual PbI 6 octahedral distortion.…”

Magic guanidinium cations in perovskite solar cells: from bulk to interface

“…3b) with corner-sharing octahedra. 32 The crystallographic data of GAPbI 3 and GA 2 PbI 4 are summarized, as shown in Fig. 3c and d, and Table 2.…”

“…Reproduced with permission. 32 Copyright 2021, ACS Publishing Group. (e) PbI 6 inorganic framework and N-HÁ Á ÁI hydrogen bonds in MAPbI 3 , FAPbI 3 , and GAPbI 3 .…”

Two metal-free perovskite molecules with different 3D frameworks show reversible phase transition, dielectric anomaly and SHG effect

“…23,24 HOIPs are a crucial group of functional materials with perovskite or perovskite-like structures formed by the self-assembly of organic cation and anion frameworks. [25][26][27][28] Among them, the organic components have some special advantages such as mechanical plasticity, structural variability, ease of processing, and greater polarity. The inorganic components in perovskites also exhibit many unique properties, i.e., semiconductor properties, photoluminescence properties, magnetic properties, mechanical stability, and thermal stability.…”