Progress in research on fluorescence lasing and kinetics of two-dimensional perovskite semiconductors

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[ Instrument Network Instrument Development ] In the new metal halide perovskite semiconductor material family, the two-dimensional Ruddlesden-Popper perovskite has the advantages of high exciton binding energy, high structural stability, natural quantum well structure, etc. Cost, flexible optoelectronic devices such as solar cells, light-emitting diodes, laser diodes, photodetectors and other fields have great potential, and also provide an ideal platform for the development of high-speed, low-power exciton devices. For example, the energy conversion efficiency of solar cells based on this type of perovskite mixed phase has exceeded 20%, and the fluorescence quantum yield is up to 80%. The room temperature exciton polarization effect has also been widely reported. Recently, Zhang Qing, a researcher at the Peking University School of Engineering, based on mechanically stripped pure phase two-dimensional perovskite flakes, reported the laser behavior depending on the number of inorganic layers (n), and studied the physical mechanism of internal energy loss. It is pointed out that the double exciton Auger recombination and exciton phonon coupling are the main loss pathways. Related work is published online at Adv. Mater. 2019, 1903030, entitled "Lasing from Mechanically Exfoliated 2D Homologous Ruddlesden - Popper Perovskite Engineered by Inorganic Layer Thickness", the first unit being the Peking University School of Engineering.
In this work, Zhang Qing's group prepared a single-component bulk single crystal of (C4H9NH3)2(CH3NH3)n-1PbnI3n+1 (n=1–5) and obtained micron-sized flakes by mechanical exfoliation. Under low temperature conditions, the two-dimensional perovskite with n≥3 can stimulate the laser out above the threshold, while for the case of n≤2, the laser/spontaneous radiation amplification cannot be obtained even if the temperature drops to 78 K. Combined with time-resolved fluorescence spectroscopy and temperature-dependent fluorescence spectroscopy, the non-radiative composite pathway is mainly composed of double exciton Auger recombination and exciton-phonon coupling. At the same time, they quantified the energy loss factors in different n-value two-dimensional perovskites. As the value of n decreases, the quantum confinement effect increases, and the Auger composite strength increases. At the same time, the lattice stiffness decreases. The sub-phonon coupling intensity increases, and the two effects cause the fluorescence lasing threshold to gradually increase as n decreases. The results of this study provide guidance for reducing the laser threshold of two-dimensional perovskites.
(a) Schematic diagram of laser characterization and energy loss path of mechanically exfoliated two-dimensional perovskite flakes; (b) laser desorption of two-dimensional perovskite flakes from n=2–5 at 78K (from left to right), n=2 can not emit laser; (c) the effective lifetime of the two-dimensional perovskite flakes with n=2–5 depends on the carrier density (top to bottom) and the corresponding fitting curve; (d) n=2–5 mechanically stripped two-dimensional perovskite fluorescence half-height width dependence on temperature (top to bottom) and corresponding fit curve
The first author of the work is the 2015 undergraduate student Liang Yin, the 2017 doctoral student Shang Qiuyu and Peking University/Northwestern Polytechnical University jointly trained doctoral student Wei Qi. The work is mainly with Professor Xing Guichuan of the University of Macau and Liu Xinfeng of the National Nanoscience Center. The researcher completed the collaboration and was assisted by researcher Ye Wei and Shi Kebin from the School of Physics, Peking University. The research has received funding support from the National Natural Science Foundation of China, the Ministry of Science and Technology Key Research and Development Program, and the Open Fund of the State Key Laboratory of Low-Dimensional Quantum Physics.

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