Regulating off-centering distortion maximizes photoluminescence in halide perovskites

December 21, 2020

In work published in the National Science Review (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-xCsxGeI3 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.
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More information: "Regulating off-centering distortion maximizes photoluminescence in halide perovskites", Lü et al., National Science Review, nwaa288, https://doi.org/10.1093/nsr/nwaa288.

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