High Pressure Study On Two-dimensional Mixed Cation Organic-inorganic Hybrid Perovskite ?Ga??Ma?₂Pb₂I₇

In recent years,organic–inorganic halide perovskites have emerged as one of the most popular optoelectronic materials owing to their outstanding performance and pro-spects in the photovoltaic and optoelectronic fields.In 2009,Tsutomu Miyasaka and colleagues in Japan reported on organic–inorganic lead halide perovskite compounds as light absorbers in dye-sensitized solar cells.The device delivered just 3.8%power conversion efficiency,at the time of writing,the record perovskite power conversion efficiency is 24.2%,certified by the National Renewable Energy Laboratory.Besides efficiency,another critical factor for photovoltaics and other optoelectronic applications is environmental stability and photostability under operating conditions.Two-dimen-sional?2D?lead halide perovskites have many advantages?e.g.,stability,tuning of op-tical and electronic properties,and the large amount of possible organic cations that can be integrated into their structure?compared to their 3D counterparts.This make them a stable alternative for efficient and large-scale module solar cells,which may constitute the next step for commercializing perovskite-based solar cells.The 2D perovskite has a unique layered configuration structure with interesting physical properties.They consists of organic layers around 1 nm thick and inorganic sheets around 0.6 nm thick.The energy gap of the organic layers is much higher than the energy gap of the inorganic layers by at least 3 eV.As a result,the 2D-layered per-ovskite material is configured as a Quantum well structure,the organic cations function as the barriers,whereas the inorganic framework functions as the well.2D organic-inorganic hybrid perovskite materials exhibit many unique properties under high pres-sure owing to this unique layered structure.Here,we systemically investigated the relationship between the structure and op-tical properties of 2D layered perovskite?C?NH₂?₃??CH₃NH₃?₂Pb₂I₇ under a high pres-sure.The emission intensity significantly increased as the pressure increased to 1.3 GPa,followed by a continuous reduction and disappearance at 7.0 GPa.Simultaneously,the bandgap first decreased,then increased,and gradually decreased again along with pres-sure elevation.The XRD result showed that the structure was stable up to 7.0 GPa and then gradually amorphized with local structure distortion.We speculated two distinct regimes of compression dominated by the alternating ordering of softer organic cation layers and less compressible inorganic octahedral layers.The color of?C?NH₂?₃??CH₃NH₃?₂Pb₂I₇ changed from black to red,then to orange-light yellow,and finally back to black during decompression from 25.1 GPa.By comparing the absorp-tion spectra and optical micrographs of?C?NH₂?₃??CH₃NH₃?₂Pb₂I₇ before compression and after decompression from 25.1 GPa,we discovered that the color turned black after compression,while it was dark red before compression;the corresponding bandgap de-creased from 2.00 eV at ambient pressure to 1.79 eV.This work paves the way to in-vestigate structure–property relationships in 2D perovskites and offers new strategies for further development of advanced perovskite devices.