Author: Song, Jiajun
Title: High-performance organic electrochemical transistors for bioelectronic applications
Advisors: Yan, Feng (AP)
Degree: Ph.D.
Year: 2022
Subject: Organic electrochemical transistors
Hong Kong Polytechnic University -- Dissertations
Department: Department of Applied Physics
Pages: xvi, 122 pages : color illustrations
Language: English
Abstract: Organic electrochemical transistors (OECTs), utilizing ion penetration into the bulk of active materials to modulate the channel conductivity, are recognized as versatile building blocks for biosensors, bioelectronic circuits, and neuromorphic applications due to their high transconductance, low working voltage, design diversity, and facile manufacturing. However, the development of OECTs is currently hampered by the lack of high-performance n-type channel materials, and the study on OECT-based integrated devices is in its infancy. In this thesis, conductive two-dimensional metal-organic frameworks (2D MOFs) are employed to develop high-performance n-type electrochemical transistors, and a novel OECT-based integrated architecture, in which an OECT is gated by a perovskite solar cell (PSC), is exploited for high-gain, ultrafast photodetectors towards remote photoplethysmogram sensors under ambient light. First, a semiconducting 2D MOF, Cu3(HHTP)2 (HHTP: 2,3,6,7,10,11­hexahydroxytriphenylene), is deployed in solution-gated transistors due to its high porosity and unique charge transport properties. An n-channel solution-gated MOF transistor (SGMT) is realized for the first time, in which the solution-processed Cu3(HHTP)2 serves as the channel material. The conductivity of the Cu3(HHTP)2 film can be significantly modulated via the ion doping from the electrolyte. The SGMT is further implemented in dopamine (DA) sensing, realizing high sensitivity and selectivity due to the oxidation of DA on the MOF channel. The proposed SGMT demonstrates the great potential of 2D MOFs for electrolyte-gated transistors.
Second, based on a microfabrication process enabling the microscale patterning of high-quality 2D MOFs, a high-performance n-type MOF electrochemical transistor (MOFECT) based on Cu3(HHTP)2 is realized, in which the efficient electrochemical doping of Cu3(HHTP)2 is evidenced by the volumetric capacitance effect. The Cu3(HHTP)2 achieves a record-high electron mobility (μe) of 0.25 cm2 V-1 s-1 in n-type OECTs due to the unique extended π-conjugated structure and retains a high volumetric capacitance C* (80.9 F cm-3) originated from the high porosity facilitating ion uptake, yielding a μeC* product of 20.3 F cm-1 V-1 s-1, which is comparable to that of state-of-­the-art n-type OECTs. Besides, the MOFECT exhibits fast response and excellent operational stability. The n-type MOFECT is successfully integrated with a p-type OECT for flexible complementary inverters, which realize a high voltage gain of 14 V V-1 and a fast response (~200 Hz) under a low working voltage of 0.4 V. This work provides an effective microfabrication protocol for 2D-MOF-based microelectronics and demonstrates that 2D MOFs are promising channel materials for high-performance electrochemical transistors. Third, a novel OECT-based integrated architecture, where an OECT is gated by a PSC, is exploited to address the trade-off between high gain and fast response in traditional photodetectors. To satisfy diverse applications, a depletion-mode OECT and an accumulation-mode OECT are respectively integrated with a PSC via solution processing, exhibiting good flexibility and robustness. OECTs with high transconductance (10.3 mS) and fast response (4.9 µs) are realized, enabling the PSC-gated OECT to detect light signals in a broad spectral range from ultraviolet (UV) to near-infrared (NIR) light with a high gain of 1 x 10 6 and an ultrafast response of 18.1 μs under a low working voltage (-0.5 V). Vertically stacked architecture is proposed to facilitate arrays fabrication, showing great potential for weak light imaging. Benefiting from the excellent figures of merit, remote photoplethysmogram sensing under ambient light is achieved, offering a convenient, low-power approach for vital signs monitoring and overcoming the discomfort and restriction on motions caused by direct skin contact. This novel monolithic architecture is demonstrated as a promising platform for developing high-performance, flexible optoelectronic devices towards low-power, user-friendly, multifunctional wearable electronics. In summary, this thesis provides a systematic study on conductive 2D MOFs for electrochemical transistors and presents a novel PSC-OECT integrated architecture, demonstrating the great potential of OECTs for bioelectronic applications.
Rights: All rights reserved
Access: open access

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