Correlating Photophysical Properties with Stereochemical Expression of 6s2 Lone Pairs in Two‐dimensional Lead Halide Perovskites

Author:

Gu Jiazhen1,Tao Yu1,Fu Tonghuan2,Guo Songhao2,Jiang Xiaofan1,Guan Yan1,Li Xiaotong3,Li Chen1,Lü Xujie2,Fu Yongping1ORCID

Affiliation:

1. Beijing National Laboratory for Molecular Science State Key Laboratory of Rare Earth Materials Chemistry and Applications College of Chemistry and Molecular Engineering Peking University Beijing 100871 China

2. Center for High Pressure Science and Technology Advanced Research (HPSTAR) Shanghai 201203 China

3. Division of Chemistry and Chemical Engineering California Institute of Technology Pasadena CA 91125 USA

Abstract

AbstractTwo‐dimensional (2D) lead halide perovskites (LHPs) have shown great promises for light‐emitting applications and excitonic devices. Fulfilling these promises demands an in‐depth understanding on the relationships between the structural dynamics and exciton‐phonon interactions that govern the optical properties. Here, we unveil the structural dynamics of 2D lead iodide perovskites with different spacer cations. Loose packing of an undersized spacer cation leads to out‐of‐plane octahedral tilting, whereas compact packing of an oversized spacer cation stretches Pb−I bond length, resulting in Pb2+ off‐center displacement driven by stereochemical expression of the Pb2+ 6s2 lone pair electrons. Density functional theory calculations indicate that the Pb2+ cation is off‐center displaced mainly along the direction where the octahedra are stretched the most by the spacer cation. We find dynamic structural distortions associated with either octahedral tilting or Pb2+ off‐centering lead to a broad Raman central peak background and phonon softening, which increase the non‐radiative recombination loss via exciton‐phonon interactions and quench the photoluminescence intensity. The correlations between the structural, phonon, and optical properties are further confirmed by the pressure tuning of the 2D LHPs. Our results demonstrate that minimizing the dynamic structural distortions via a judicious selection of the spacer cations is essential to realize high luminescence properties in 2D LHPs.

Funder

National Natural Science Foundation of China

Publisher

Wiley

Subject

General Chemistry,Catalysis

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