Regulating off-centering distortion maximizes photoluminescence in halide perovskites - Dr. Xujie Lü

DECEMBER 21, 2020

In work published in the journal of National Science Review ("Regulating off-centering distortion maximizes photoluminescence in halide perovskites",  https://doi.org/10.1093/nsr/nwaa288), a team at HPSTAR led by Dr. Xujie Lü applied high pressure to tune the remarkable photoluminescence (PL) properties in halide perovskites. For the first time, they reveal a universal relationship whereby regulating the level of off-centering distortion (towards 0.2) can achieve optimal PL performance.

The extraordinary electronic and optical properties that halide perovskites possess have revolutionized next-generation photovoltaics and optoelectronics’ prospects. However, the underlying mechanisms responsible for their unique functionalities are still not fully understood. Developing our fundamental understanding of how structural configurations affect their properties is crucial. As a thermodynamic variable, pressure can effectively tune the lattice and electronic configurations, resulting in concomitant changes in materials’ properties.

Using advanced in situ/operando high-pressure techniques in combination with theoretical calculations yielded fascinating results. “By carefully selecting and regulating the highly-distorted halide perovskites, we reached an otherwise unreachable structural region for probing properties that affords a great opportunity to understand the structure-property relationship,” said Dr. Lü.

The team applied their obtained principle as a guideline to achieve bright PL in (CH₃NH₃)_1-xCs_xGeI₃ by chemically substituting CH₃NH₃⁺ with smaller sized Cs⁺. The chemical substitution tunes the distortion, much like external pressure. The compression of CsGeI₃ further regulates the distortion to the optimal value at 0.7 GPa, which maximizes the emission with a ten-fold enhancement. These findings open new paths to high-performance optoelectronic materials by leveraging the distortion and strain degrees of freedom.

“This work not only demonstrates the quantitative relationship between structural distortion and the PL property of halide perovskites,”said Dr. Lü, “but also illustrates the use of the extracted knowledge for the virtuous cycle of materials design and optimization.”

This direct use of knowledge gained from high-pressure research to purposefully design and synthesize materials with desired properties at ambient conditions is rarely reported.

Caption: Pressure-regulated off-centering distortion maximizes photoluminescence in halide perovskites.

 以CH₃NH₃PbI₃为代表的金属卤化物钙钛矿材料由于其独特的电子结构和光电特性，已经为光电器件带来了革命性的发展。然而，高效钙钛矿材料中铅的毒性与本身的不稳定性极大阻碍其在光电领域的发展和应用。为了设计开发安全、稳定、性能优异的新型钙钛矿光电材料，需要对其性能独特的内在机理以及结构物性关系有深刻的理解和认识，特别是晶格畸变和电子缺陷对性能的影响机制。为此，北京高压科学研究中心吕旭杰课题组与美国西北大学Mercouri G. Kanatzidis教授团队等通力合作，通过优选一系列具有独特畸变结构的锗基钙钛矿材料，利用压力调控结合化学方法揭示了卤化物钙钛矿定量构效关系并提出实现最佳发光性能的结构畸变参数，相关成果以题为“Regulating off-centering distortion maximizes photoluminescence in halide perovskites”近期发表于《国家科学评论》（National Science Review）。