Author: Loi, Hok Leung
Title: Highly sensitive photodetectors based on dimensionally and compositionally modulated perovskites
Advisors: Yan, Feng (AP)
Degree: M.Phil.
Year: 2020
Subject: Optical detectors
Hong Kong Polytechnic University -- Dissertations
Department: Department of Applied Physics
Pages: xv, 90 pages : color illustrations
Language: English
Abstract: Photodetector, which harvests light and converts it into electrical signals, is one kind of essential optoelectronic device extensively used in fields of environmental monitoring, imaging, optical communication, and biomedical sensing. Organic-inorganic halide perovskites (e.g., MAPbI3) have been regarded as revolutionary candidate materials for photodetectors because of their outstanding optoelectronic property and low-temperature solution processability, which require simple manufacturing technologies and low-cost facilities to attain sizeable photoresponse. Likewise, the optimal performance of perovskite photodetectors (PPDs) has grown to a level comparable to those of main inorganic semiconductor materials (e.g., MoS2, WSe2, Graphene, and Si) in commercial market. Notably, various types of halide perovskite materials have recently developed based on their outstanding structural and compositional tunability. In this thesis, the dimensional and compositional modulations on perovskite materials were reviewed briefly. Then, the working mechanisms, performance parameters and sensing applications of PPDs were systematically investigated. My works were mainly divided into two parts. The first one was a series of (PEA)2(MA)n−1PbnI3n+1 perovskite thin films designed and fabricated by a convenient hot-casting method to obtain gradient n-number in the films, which can lead to the formation of vertical two- /three-dimensional (2D/3D) heterojunctions that can enhance charge separation in the films under light illumination. Based on a single gradient perovskite film, the optimal photodetector exhibited the high responsivity of 149 AW−1 and specific detectivity of 2 × 1012 Jones. This work opens up the possibility of constructing a type of dimensionally graded perovskite heterojunction in high-performance optoelectronic devices. Another work was to apply the Sn-containing perovskite alloy MA0.5FA0.5(Pb1-xSnx)I3 with a bandgap lower than those of both end compounds as a photoactive layer in the near-infrared (NIR) photodetectors. Here, a high-performance phototransistor based on a single layer of Sn/Pb-based perovskite alloy has been demonstrated with ultrahigh responsivity of ~ 106 AW-1 and specific detectivity of ~ 1014 Jones in NIR-II region. Although Sn/Pb-based perovskite alloys are successful introduced in solar cells and even in photoconductors and photodiodes, they have never been used in phototransistors until now. This work provides a promising composition control technique for future exploration of ultrasensitive broadband perovskite phototransistors.
Rights: All rights reserved
Access: open access

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