What happens to zero-dimensional metal halide perovskites at high pressure?

Developing an effective strategy to improve the optical properties of inorganic metal halide remains a pressing challenge. Here the authors demonstrate that an intriguing emission of isolated octahedra within zero-dimensional metal halide perovskites can be achieved via diamond anvil cell.
Published in Chemistry
What happens to zero-dimensional metal halide perovskites at high pressure?

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The recent success of organometallic halide perovskite nanocrystals (NCs) in photovoltaic devices has further triggered research activities on inorganic metal halide perovskite (MHP) NCs due to their good stability compared to their organic counterparts. Furthermore, developing an effective strategy to improve the optical properties of MHPs remains a pressing challenge. The cesium lead halide perovskite of Cs4PbBr6 is a typical zero-dimensional (0D) inorganic MHP, in which the octahedra are completely isolated by cation bridges and charge carriers are localized within the ordered metal halide component. Based on the previous established reports, the formation of localized self-trapped exciton (STE) is critically dependent on the dimensionality of the crystalline systems, and lowering the dimensionality makes exciton self-trapping easier. Therefore, 0D systems with strong confinement are reasonably expected to be favorable for the formation of STEs. 

Intriguingly, the initially nonfluorescent 0D perovskite Cs4PbBr6 NCs exhibit a distinct emission under a high pressure of 3.01 GPa. Subsequently, the emission intensity of Cs4PbBr6 NCs experiences a significant increase upon further compression. Joint experimental and theoretical analyses indicate that such pressure-induced emission (PIE) may be ascribed to the enhanced optical activity and the increased binding energy of self-trapped excitons upon compression. This phenomenon is a result of the large distortion of [PbBr6]4− octahedral motifs resulting from a structural phase transition. Our findings demonstrate that high pressure can be a robust tool to boost the photoluminescence efficiency and provide insights into the relationship between the structure and optical properties of 0D MHPs under extreme conditions.

How can we see the rainbow without experiencing a rainy day? After an arduous experience, it is very exciting for us to achieve this great success. Our results suggest that pressure processing offers an exciting means to achieve perovskite materials that may show enhanced functional properties upon overcoming the limitations of conventional synthetic chemistry. Nonetheless, I would like to express that the concept of PIE proposed by this work is more important than the result itself.

The published work is indeed the result of a truly multi-team effort that led to beautiful research. Also, we would like to express our sincere gratitude to Prof. Lijun Zhang, Prof. Simon A.T. Redfern and anonymous referees for their invaluable comments in improving this work. Many thanks also go to my supervisors, Prof. Bo Zou and Prof. Guangtian Zou, for their fruitful discussions on the project. This paper is dedicated to Prof. Guangtian Zou on the occasion of 80th birthday, and please send my best wishes.

To learn more about our work, you can read it here: Nature Communications, Volume 9, Article number 4506 (2018),  https://www.nature.com/articles/s41467-018-06840-8 by Zhiwei Ma, Zhun Liu, Siyu Lu, Lingrui Wang, Xiaolei Feng, Dongwen Yang, Kai Wang, Guanjun Xiao, Lijun Zhang, Simon A.T. Redfern & Bo Zou. 

Written by Guanjun Xiao, associate professor at State Key Laboratory of Superhard Materials, College of Physics, Jilin University.

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