Browsing by Author "Liu, Fangzhou"

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High optical nonlinearity in low-dimensional halide perovskite polycrystalline films
(2020-08-17)
Liang, Wei-Yun
;
Liu, Fangzhou
;
Lu, Yu-Jung
;
Popovic, Jasminka
;
Djurisic, Aleksandra
The nonlinear optical properties of low-dimensional polycrystalline halide perovskite films consisting of ethylammonium (EA) and butylammonium (BA) cations are investigated using Z-scan technique. Across the band-edge, two-dimensional (BA)(2)PbI4 exhibits a transition from saturable absorption (SA) to reverse-SA and its nonlinear absorption and nonlinear refractive index are much smaller than those of bulk counterparts. Meanwhile, EAPbI(3) with one-dimensionality of the inorganic structure shows the SA behavior both above and below band-edge and the estimated nonlinear optical parameters of polycrystalline EAPbI(3) are comparable to those of single-crystalline ones, attributed to high dielectric contrast between the inorganic and organic elements in one-dimensional structures. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Structure-Dependent Photoluminescence in Low-Dimensional Ethylammonium, Propylammonium, and Butylammonium Lead Iodide Perovskites
(2020-01-29)
Lin, Chang-Wei
;
Liu, Fangzhou
;
Chen, Ting-Yang
;
Lee, Kuan-Hua
;
Chang, Chung-Kai
Hybrid organic-inorganic perovskites have attracted great attention as the next generation materials for photovoltaic and light-emitting devices. However, their environment instability issue remains as the largest challenge for practical applications. Recently emerging two-dimensional (2D) perovskites with Ruddlesden-Popper structures are found to greatly improve the stability and aging problems. Furthermore, strong confinement of excitons in these natural quantum-well structures results in the distinct and narrow light emission in the visible spectral range, enabling the development of spectrally tunable light sources. Besides the strong quasi-monochromatic emission, some 2D perovskites composed of the specific organic cations and inorganic layer structures emit a pronounced broadband emission. Herein, we report the light-emitting properties and the degradation of low-dimensional perovskites consisting of the three shortest alkylammonium spacers, mono-ethylammonium (EA), n-propylammonium (PA), and n-butylammonium (BA). While (BA)(2)PbI4 is known to form well-oriented 2D thin films consisting of layers of corner-sharing PbI6 octahedra separated by a bilayer of BA cations, EA with shorter alkyl chains tends to form other types of lower-dimensional structures. Nevertheless, optical absorption edges of asprepared fresh EAPbI(3), (PA)(2)PbI4, and (BA)(2)PbI4 are obviously blue-shifted to 2.4-2.5 eV compared to their 3D counterpart, methylammonium lead iodide (MAPbI(3)) perovskite, and they all emit narrow excitonic photoluminescence. Furthermore, by carefully optimizing deposition conditions, we have achieved a predominantly 2D structure for (PA)(2)PbI4. However, unlike (BA)(2)PbI4, upon exposure to ambient environment, (PA)(2)PbI4 readily transforms to a different crystal structure, exhibiting a prominently broadband light from similar to 500 to 800 nm and a gradual increase in intensity as structural transformation proceeds.