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" van der Waals Heterostructure Devices — From Two-dimensional Materials to Hybrid Perovskites "
Cheng, Hung-Chieh
Huang, Yu
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Latin Dissertation
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English
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897551
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TL09p0q9bx
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| Main Entry
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Walsh, Carolyn Meta
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| Title & Author
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van der Waals Heterostructure Devices — From Two-dimensional Materials to Hybrid Perovskites\ Cheng, Hung-ChiehHuang, Yu
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| Date
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2016
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2016
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| Abstract
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Graphene, since its discovery in 2004, has stimulated considerable interest in two- dimensional layered materials research (2DLMs). Various applications have been investigated with the ever-expanding family of 2D materials, ranging from electronic, optoelectronic, sensing, energy storage and catalytic applications, etc. With weak van der Waals forces between layers, generally, 2DLMs can be exfoliated into atomically thin sheets and reassembled in a designed sequence for building artificial heterostructures, namely, van der Waals heterostructures (vdWHs). Except for the most common 2D material — graphene, the building blocks for vdWHs also include semiconductors, insulators and even metallic materials. Such versatility has rendered vdWHs become a promising platform for high performance electronic and optoelectronic devices. Researchers have shown that the devices based vertically stacked vdWHs could be the candidates for transistors (barristors), photodetectors, light-emitting diodes and flexible electronics, etc. Particularly, the unique electronic properties of graphene have been playing very important roles in these vertically stacked vdWH devices. In addition to the transparency and extraordinary electrical conductivity of graphene, the work function of graphene can be modulated by varying the gate electric field, enabling a tunable electrical contact with other materials. With the experience we have built up with 2D materials, we further explored the possibilities of integrating a new category of materials – organic- inorganic hybrid perovskites. The hybrid perovskites are the newly emerging materials for high performance optoelectronic applications, which are mostly investigated for solar cell applications. The perovskite based solar cells have shown an astonishing improvement in power conversion efficiency from 3.8 to 22.1% in just few years. Such prominent performance has attracted tremendous research interests from different perspectives. However, these perovskite materials are generally not compatible with conventional nanodevice fabrication due to their considerable solubility in polar organic solvent and water. Despite such fabrication difficulties, we have proposed several approaches to fabricate electronic and optoelectronic devices based on the integration of perovskites and 2D materials. In this dissertation, I will show how we develop a universal water-free dry transfer method to solve the fabrication problems of perovskites and how we build new types of vdWHs with perovskites and 2D materials. We have realized the first van der Waals heterojunction devices based on perovskites and 2D materials, and achieved a high photo- responsivity (950 A/W) and a very high photoconductive gain (~2200) with graphene/perovskite/graphene vertical structure. Moreover, a unique and prominent gate-tunable photovoltaic effect has been observed in the vertically stacked perovskite/WSe2 heterojunction devices. Finally, we have investigated the doping effect induced by ionic solid and the ion migration in perovskites. A switchable p-n junction formation has been demonstrated on a monolayer WSe2 device by electrical poling, along with a very high external quantum efficiency up to 93% under the excitation of 532 nm laser. I believe that in the near future, such platform can enable more possibilities in both electronic and optoelectronic applications with the expanding 2D materials family and hybrid perovskites with compositional tunability.
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Cheng, Hung-Chieh
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UCLA
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