Browsing by Author "Shuai, Xinting"

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    Morphology controlled All-Inorganic 2D Perovskite and Transition-Metal Dichalcogenides materials synthesis, characterization and application
    (2023-09-01) Shuai, Xinting; Mohite, Aditya D; Ajayan, Pulickel M
    In recent years, 2D hybrid Ruddlesden-Popper (RP) halide perovskites have garnered significant attention due to their tunable optical and electronic properties alongside impressive stability. Their versatile applications span fields such as light emitting diodes (LEDs), field-effect transistors (FETs), photodetectors, and solar cells. This thesis delves into the evolution of traditional metal halide perovskites and 2D RP perovskites. Notably, emerging within this landscape are the all-inorganic 2D RP Cs2PbI2Cl2 (Pb-based n=1) and Cs2SnI2Cl2 (Sn-based n=1) perovskites, recognized for robust UV-light responsiveness, thermal stability, and remarkable carrier mobility. An innovative achievement is the synthesis of Pb and Sn-based n=1 2D RP perovskite films boasting sub-millimeter single crystal grains via a one-step CVD process at atmospheric pressure. These perovskites showcase a distinctive "tiled" crystal morphology and horizontally-oriented octahedral layers. The study advances to encompass the pioneering fabrication of multilayered Cs3Pb2I3Cl4 (Pb-based n=2) and Cs3Sn2I3Cl4 (Sn-based n=2) films, characterized by X-ray diffraction (XRD) and density functional theory (DFT) calculations for refined crystallographic structures. Complementary DFT calculations and experimental optical spectroscopy discern bandgap energy shifts attributable to quantum confinement effects. Intriguingly, a bias-free photodetector is realized using Sn-based n=1 perovskite, showcasing reproducible photocurrent and a swift 84ms response time. This research underscores the feasibility of growing substantial all-inorganic multilayered 2D perovskite crystals through a singular CVD process, propelling their potential as viable candidates for future photovoltaic applications. Additionally, exploration into using chloride and bromide as halide constituents yields large-area CsPbI2Br films on FTO substrate and CsPbI2Br nanowires on SiO2/Si substrate via the CVD method. Furthermore, the scope broadens to Transition-Metal Dichalcogenides materials, another semiconductor class commonly grown through CVD. Tailoring flow rates facilitates the fabrication of expansive MoS2 and WS2 films via a salt-assisted approach. For gas sensor applications, various chip treatment methodologies including wet-transfer, maskless lithography, and O2 plasma etching are investigated.
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    Revealing the impact of ammonium ions from different low-dimensional perovskite structures on the film formation and degradation mechanism of FAPbI3 via sequential deposition
    (AIP Publishing LLC, 2024) Wang, Yafei; Yuan, Shihao; Feng, Rongsen; Diao, Zecheng; Huang, Jie; Liao, Jiacai; Sidhik, Siraj; Shuai, Xinting; Wang, Meicong; Zou, Tao; Liang, Zhongwei; Zhang, Ting; Mohite, Aditya D.; Li, Shibin
    In recent years, the organic–inorganic hybrid perovskite community has been widely employed as the photo-active layer in optical-electronic devices. The black α-phase formamidinium lead iodide (FAPbI3) is the most popular perovskite for realizing high-efficiency solar cells due to its suitable bandgap. However, the issue of stability is also a concern in the research on FAPbI3 solar cells. In this study, different ammonium ions, such as butylamine (BA), guanidine (GA), and butylene diamine (BDA), which are commonly used to construct two-dimensional perovskites, including Ruddlesden–Popper, Dion–Jacobson, and alternating cations in the interlayer space, respectively, were introduced in the fabrication of FAPbI3 using a sequential deposition method. Several structures of PbI2 precursor films were formed by introducing the aforementioned ions, which exhibited different arrangements and connection modes in lead iodides. BA-PbI2 precursor films exhibited higher specific surface areas, which were beneficial to the diffusion, ion exchange, and sequential reaction of FA+. The BDA-PbI2 precursor film slowed down the sequential reaction of FAPbI3 because of reduced van der Waals bonds. The nucleation dynamics and degradation processes of perovskites were deeply investigated in this study. Solar cells based on BA-PbI2, GA-PbI2, and BDA-PbI2 were also fabricated.