Structural Damage of Two-Dimensional Organic–Inorganic Halide Perovskites

Biao Yuan,Chao Liang,Letian Dou,Enzheng Shi,Yi Yu

doi:10.3390/inorganics8020013

Biao Yuan, Chao Liang + Show 3 more

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https://doi.org/10.3390/inorganics8020013

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Abstract

Organic–inorganic halide perovskites are promising photovoltaic materials with excellent optoelectronic properties. However, the extreme structural instability hinders their wide application as well as the microstructure characterization using high energy beams such as transmission electron microscopy (TEM). Here, taking BA2FAPb2I7 and BA2MAPb2I7 as examples, we investigate their structural evolution resulting from high energy electron irradiation, moist air, and low temperature, respectively. The results show that the long organic chains are the first to be damaged under electron beam, which is mainly arising from their instability and weak bonding with the framework of [PbI6]4− octahedrons. Then the short organic cations and the framework of [PbI6]4− octahedrons collapses gradually. The final products are clusters of detached PbI2 particles, which can also be observed in the sample degraded in moist air. In addition, the structures of BA2FAPb2I7 and BA2MAPb2I7 are discovered to undergo a phase transformation at liquid nitrogen temperature, which calls attention to the community that cryo-TEM methods should be used cautiously for organic–inorganic halide perovskite materials.

Highlights

Two-dimensional (2D) organic–inorganic halide perovskites have attracted significant research interests owing to their wide tunability and excellent optical/electronic properties [1,2]
Transmission electron microscopy (TEM) has been widely used to study the crystal structure and real atomic resolution is achieved in the recent decades owing to aberration correction [8]
After the organic-chain layer disordered, further electron irradiation causes damage to the short organic cations, and the inorganic layers and entire framework of the structure collapses into small particles

Summary

Introduction

Two-dimensional (2D) organic–inorganic halide perovskites have attracted significant research interests owing to their wide tunability and excellent optical/electronic properties [1,2]. The perovskite bulk structure has the general formula of ABX3 , where the A-site cations are normally inorganic alkali ions Cs+ , Rb+ , or can be substituted by short organic cations CH3 NH3 + (methylammonium, MA) or CH(NH2 )2 + (formamidinium, FA). In contrast to the bulk perovskites, 2D halide perovskites are usually formed in organic–inorganic hybrid phases, with separated octahedral [BX6 ]4− layers jointed by long organic chains, such as n-butylammonium (n-BA+ ), bithiophene (2T), and tetrathiophene (4T). Transmission electron microscopy (TEM) has been widely used to study the crystal structure and real atomic resolution is achieved in the recent decades owing to aberration correction [8]. With carefully controlling of the electron dose, atomic resolution has been demonstrated on the inorganic 2D halide

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