@article{5705ec59d53b492db27c59a632bb05bb,
title = "Enhanced Exciton and Photon Confinement in Ruddlesden–Popper Perovskite Microplatelets for Highly Stable Low-Threshold Polarized Lasing",
abstract = "At the heart of electrically driven semiconductors lasers lies their gain medium that typically comprises epitaxially grown double heterostuctures or multiple quantum wells. The simultaneous spatial confinement of charge carriers and photons afforded by the smaller bandgaps and higher refractive index of the active layers as compared to the cladding layers in these structures is essential for the optical-gain enhancement favorable for device operation. Emulating these inorganic gain media, superb properties of highly stable low-threshold (as low as ≈8 µJ cm−2) linearly polarized lasing from solution-processed Ruddlesden–Popper (RP) perovskite microplatelets are realized. Detailed investigations using microarea transient spectroscopies together with finite-difference time-domain simulations validate that the mixed lower-dimensional RP perovskites (functioning as cladding layers) within the microplatelets provide both enhanced exciton and photon confinement for the higher-dimensional RP perovskites (functioning as the active gain media). Furthermore, structure–lasing-threshold relationship (i.e., correlating the content of lower-dimensional RP perovskites in a single microplatelet) vital for design and performance optimization is established. Dual-wavelength lasing from these quasi-2D RP perovskite microplatelets can also be achieved. These unique properties distinguish RP perovskite microplatelets as a new family of self-assembled multilayer planar waveguide gain media favorable for developing efficient lasers.",
keywords = "exciton confinement, high stability, low-threshold lasing, photon confinement, Ruddlesden–Popper perovskites",
author = "Mingjie Li and Qi Wei and Muduli, {Subas Kumar} and Natalia Yantara and Qiang Xu and Nripan Mathews and Mhaisalkar, {Subodh G.} and Guichuan Xing and Sum, {Tze Chien}",
note = "Funding Information: microplatelet as shown by top-view scanning electron microscopy (SEM), and optical and atomic force microscopy (AFM) images (see Figure 1c and Figures S2–S4 in the Supporting Information). Consistent with the PL results, the X-ray diffraction (XRD) pattern (Figure 1d) reveals that the multiple diffraction peaks originate from stacked quasi-2D RP perovskite QWs ranging from n = 2 to n ≥ 6. A detailed analysis of the XRD pattern is presented in Figures S5 and S6 in the Supporting Information. The cross-sectional view SEM images at the MPL end (Figure 1e) and the cleaved facet (Figure 1f) clearly show that MPL comprised of stacked multilayers with sharp interfaces. The thickness of each layer ranges between ≈20 and 100 nm. Considering the smallest interlayer spacing is ≈2.7 nm for stacked n = 2 perovskite QW, each RP perovskite layer in MPL may contain at most approximately 40 stacks of QWs connected by van der Waals interactions.[16] These RP perovskite layers undergo further stacking and self-assembly to form an MPL (Figure 1c) as schematically shown in the inset of Figure 1d. The overall thickness of the MPLs is around ≈300–500 nm (see AFM images in Figure S4 in the Supporting Information) with near vertically edges. To further determine the contents of different dimensional perovskite layers in each MPL, micro-PL and micro-TA spectroscopies were performed (see later discussion). We also expect that these RP perovskite layers with different dimensions (i.e., each layer with a specific n value) are stacked randomly without preferential ordering in the MPLs. This hypothesis is supported by the similar PL spectra obtained for the front-side and substrate-side excitations. Funding Information: The authors thank Dr. Ankur Solanki and Ms Zhang Qiannan for their assistance with the AFM measurements. The authors acknowledge the financial support from the Ministry of Education Academic Research Fund Tier 1 grants RG101/15 and RG173/16 and Tier 2 grants MOE2015-T2-2-015 and MOE2016-T2-1-034, the NTU-A*STAR Silicon Technologies Center of Excellence Program Grant 11235100003, and the Singapore National Research Foundation through the Singapore?Berkeley Research Initiative for Sustainable Energy (SinBeRISE) CREATE Program and the Competitive Research Program NRF-CRP14-2014-03. G.C.X. acknowledges financial support from the Science and Technology Development Fund from Macau SAR (FDCT-116/2016/A3, FDCT-091/2017/A2) and Start-up Research Grant (SRG2016-00087-FST) from Research & Development Office at the University of Macau, and the Natural Science Foundation of China (91733302, 61605073, 2015CB932200), and the Young 1000 Talents Global Recruitment Program of China. Publisher Copyright: {\textcopyright} 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim",
year = "2018",
month = jun,
day = "6",
doi = "10.1002/adma.201707235",
language = "English",
volume = "30",
journal = "Advanced Materials",
issn = "0935-9648",
publisher = "Wiley-Blackwell",
number = "23",
}