Author: Liu, Chun Ki
Title: High-performance optoelectronic devices based on novel functional materials
Advisors: Yan, Feng (AP)
Degree: Ph.D.
Year: 2023
Subject: Optoelectronic devices
Hong Kong Polytechnic University -- Dissertations
Department: Department of Applied Physics
Pages: xxiv, 133 pages : color illustrations
Language: English
Abstract: Photodetectors (PDs) transform incident optical energy into electronic signal. It has been successfully integrated into various engineering systems and applications like optical communications, environmental monitoring and scientific research. However, the traditional semiconductors and devices fail to support emerging applications such as artificial eyes and low-cost wearable electronics, mainly due to their rigidity and high fabrication cost. Intensive research effort has been put in developing next-generation semiconductors and device structures to fulfil the new requirements. Among those materials, organic-inorganic hybrid perovskites (OIHPs) and two-dimensional conjugated metal–organic frameworks (2D c-MOFs) show huge potential due to their unique physical properties.
In this thesis, high-performance PDs based on novel OIHPs and 2D c-MOFs are fabricated through solution processing. Comprehensive device measurements are provided with detailed materials characterizations. The device physics are carefully studied. Those materials include a Sn-based perovskite, a quasi-2D perovskite and two promising new 2D c-MOF materials.
A low-cost solution-processed high-performance PD based on Sn-based perovskite/organic semiconductor vertical heterojunction is developed. The device exhibits broadband response from UV to NIR. The responsivity and gain are up to 2.6 × 106 A/W and 4.7 × 106, respectively. Moreover, much faster response speed and higher detectivity can be achieved by reducing the thickness of organic semiconductor. This work opens up a window for enhancing device performance of Sn-based perovskite PDs by vertical heterojunctions.
Then, another sensitive phototransistor based on quasi-2D perovskite/single-walled carbon nanotubes (SWCNTs) have been fabricated. The high optical absorption, direct band gap nature and self-constructed gradient heterojunction of the quasi-2D perovskite synergize well with the high mobility of SWCNTs. The resultant responsivity and detectivity are as high as 2 × 106 A/W and 7 × 1014 Jones, respectively. In addition, high on/off ratio of ~103 is obtained. The promising potential of such phototransistors for next-generation PDs has been demonstrated.
Next, high-quality wafer-scale thin film of a promising 2D c-MOF, Cu3(HHTT)2 (HHTT: 2,3,7,8,12,13-hexahydroxytetraazanaphthotetraphene) is demonstrated. Its semiconducting nature and charge transport mechanism are carefully studied by various temperature direct current (DC) and frequency dependent alternating current (AC) measurements. Ultrabroadband flexible photoconductor based on Cu3(HHTT)2 is fabricated. Reliable response from UV to mid-IR can be obtained, outperforms previous solution-processed broadband PDs. The device also shows typical synaptic properties and outstanding data recognition efficiency in an artificial neural network (ANN). Furthermore, ultrathin Cu3(HHTT)2 thin films can be used as hole transporting layer (HTL) for perovskite solar cells, which significantly enhances the power conversion efficiency (PCE). This work paves the way for developing high-performance optoelectronic devices based on 2D c-MOFs.
Finally, the thin film form of another novel 2D c-MOF, Cu3(HHHAT)2 (HHHAT: Hexahydroxy-hexaaza-trinapthylene). Materials characterizations clearly show that high quality oriented thin film is obtained. Broadband PDs from UV to NIR based on Cu3(HHHAT)2 is fabricated with reliable photo-response. The field-effect modulation of channel conductivity and more importantly ferroelectric memory effect is then demonstrated through top-gated device structure for the first time. This work opens up a window for the development of high-performance (opto)electronic devices based on Cu3(HHHAT)2 thin film.
Rights: All rights reserved
Access: open access

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