| 1. |
- Chen, Miaoxiang, 1962-
(författare)
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Electrochemical and electronic devices based on low bandgap polymers
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The research field of the organic electronics includes light emitting diodes (OLEDs), field-effect transistors (OFETs), polymer photovoltaic cells (PVCs), polymer lasers and electrochemical devices. Recently, organic materials are envisaged for spintronics. This dissertation covers a large research scope ranging from electrochemical devices, light emitting diodes, to field-effect transistors, in both processing techniques and device characterizations.Printed all-organic electrochemical diodes and transistors on flexible plastic or paper substrates have been realized by simple and low-cost method of fabricating. Conducting polymer poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), utilized as active component, is deposited by spin-coating or printing techniques. The devices are directly fabricated from design without the need for masks, patterns or dies. The output characteristics of both half-wave and full-wave rectifier circuits from two-terminal diodes show stable performances at frequencies of 5 Hz. Electrochemical transistors based on both three- and four-terminal configurations have good performances with IONlIoFF current ratios of 103 - 104 at operating voltages below 3 V. The new kind of devices reported are robust and could serve as components in microelectronics, and as redox sensors and detectors since the conductivity of conducting polymers depends on the redox states.Both LEDs and FETs are realized from a low bandgap donor-acceptor-donor (D-A-D) polymer. The polymer consists of fluorene units and donor-acceptor-donor (D-A-D) units. The D-A-D segment includes two electron-donating thiophene rings combined with a thiadiazolo-quinoxaline unit, which is electron withdrawing to its nature. The resulting polymer is conjugated and has a band gap of 1.27 eV. The corresponding electro- and photoluminescence spectra both peak at approximately 1 Ilm, which is largest emission wavelength ever reported to date. The resulting FETs exhibit typical p-channel functions, and relatively high field-effect mobility of 0.03 cm2y-1s-1, near zero threshold voltage and a current on/off ratio of 5 x104 in ambient atmosphere. The mobility value is highest in low bandgap D-A-D polymers ever reported so far.
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| 2. |
- Gladisch, Johannes, 1987-
(författare)
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Investigating volume change and ion transport in conjugated polymers
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Volume changes are the foundation for a wide range of phenomena and applications, ranging from the movement of plants to valves and drug delivery devices. Therefore, it does not come as a surprise that controlled volume changes are an interesting topic of research. In this thesis, volume changes in polymers are the object of investigation. Polymers are a class of macromolecules that comprise repetitive units. Owing to the wide variety of such units, polymers can exhibit manifold properties, including but not limited to strong water attraction and electrical conductivity. The former is the defining property in polymer hydrogels while the latter is a core property of conducting polymers. Both the water attracting properties and conductivity are closely linked to transport events on a molecular level. In the case of hydrogels, it is predominantly water uptake, while in the case of conducting polymers it is a complex interplay between charges, ionic charge balancing entities and water. However, in either case the transport events lead to volume changes. Despite the similarities, the properties of the materials differ greatly. On the one hand volume changes in hydrogels are very large but hard to control. On the other hand, volume changes in conducting polymers are much smaller than in hydrogels, but the control is easier due to the electronic addressing. P(gXTX) polymers combine a conducting polymer backbone with hydrogel sidechains. As described in publication 1, this combination of molecular entities was found to enabled unique properties of an electrically controllable giant volume change and concomitant solid-gel transition. In the second publication, the effect of the side chain lengths on the volume change properties of the polymers were explored. The knowledge acquired from these studies helped us to develop an electroactive filter based on p(gXTX) polymers which enabled electrochemical modulation of flow (publication 3). The aim of the fourth publication was to study the complex electronic-ionic transport processes and volume changes in a model conducting polymer, PEDOT:Tos. The understanding of fundamental processes and properties of controllable volume changes may pave the way for advances in various applications, including electroactive meshes, actuators and drug delivery devices.
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| 3. |
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| 4. |
- Liu, Jiang
(författare)
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Light-Emitting Electrochemical Transistors
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the discovery of conductive polymers in 1977, the implementation of organic conjugated materials in electronic applications has been of great interest in both industry and academia. The goal of organic electronics is to realize large-area, inexpensive and mechanically-flexible electronic applications.Organic light emitting diodes (OLEDs), as the first commercial product made from organic conjugated polymers, have successfully demonstrated that organic electronics can make possible a new generation of modern electronics. However, OLEDs are highly sensitive to materials selection and requires a complicated fabrication process. As a result, OLEDs are expensive to fabricate and are not suitable for low-cost printing or roll-to-roll process.This thesis studies an alternative to OLEDs: light-emitting electrochemical cells (LECs). The active materials in an LEC consist of a conjugated light-emitting polymer (LEP) and an electrolyte. Taking advantage of electrochemical doping of the LEP, an LEC features an in-situ formed emissive organic p-n junction which is easy to fabricate. We aim to control the electrochemical doping profile by employing a “gate” terminal on top of a conventional LEC, forming a lightemitting electrochemical transistor (LECT). We developed three generations of LECTs, in which the position of the light-emitting profile can be modified by the voltage applied at the gate electrode, as well as the geometry of the gate materials. Thus, one can use this structure to achieve a centered light-emitting zone to maximize the power-conversion efficiency. Alternatively, LECTs can be used for information display in a highly integrated system, as it combines the simultaneous modulation of photons and electrons.In addition, we use multiple LECs to construct reconfigurable circuits, based on the reversible electrochemical doping. We demonstrate an LEC-array where several different circuits can be created by forming diodes with different polarity at different locations. The thereby formed circuitry can be erased and turned into circuitry with other functionality. For example, the diodes of a digital AND gate can be re-programmed to form an analogue voltage limiter. These reprogrammable circuits are promising for fully-printed and large-area reconfigurable circuits with facile fabrication.
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| 5. |
- Luo, Yifei, et al.
(författare)
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Technology Roadmap for Flexible Sensors
- 2023
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Ingår i: ACS Nano. - : American Chemical Society. - 1936-0851 .- 1936-086X. ; 17:6, s. 5211-5295
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Forskningsöversikt (refereegranskat)abstract
- Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.
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| 6. |
- Matyba, Piotr, 1982-
(författare)
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Polymer light-emitting electrochemical cells : Utilizing doping for generation of light
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current implementation of conjugated polymers (“conducting plastics”) in a wide range of devices promises to bring the vision of a new generation of flexible, efficient and low-cost applications to reality. Plastic lightemitting devices in the form of polymer light-emitting diodes (PLEDs) are projected to be particularly close to the market in applications such as large area and conformable illumination panels and high-performance thin displays. However, two notable drawbacks of PLEDs are that they depend on vacuum deposition of a reactive metal for the negative electrode and that the active material must be extremely thin and uniform in thickness. As a consequence, PLEDs cannot be expected to allow for a low-cost continuous production using a roll-to-roll coating and/or printing process. This thesis focuses on an alternative to the PLED: A light-emitting electrochemical cell (LEC). LECs comprise a mixture of a conjugated polymer and a solid-state electrolyte as the active material positioned between two electrodes. The existence of mobile ions in the active material allows for a number of interesting attributes, both from a fundamental science and an application perspective. Importantly, the ions and the related unique operation of LECs make these devices apt for the utilization of low-cost roll-to-roll fabrication of the entire device as the electrode materials can be air stable and solution-processible and the requirement on the thickness of the active material is much less stringent than in PLEDs. The herein presented “basic science” studies primarily focus on the operation of LECs. It is for instance firmly established that a light-emitting p-n junction can form in-situ in a LEC device during the application of a voltage. This dynamic p-n junction exhibits some similarities, but also distinct differences, in comparison to the static p-n junctions that are exploited in crystalline inorganic semiconductor devices. We have also systematically explored the role that the constituent materials (ions, conjugated polymer, ionic solvent, and electrode material) can have on the performance of LECs, and two of the more important findings are that the concentration of ions can influence the doping structure in a motivated fashion and that it is critically important to consider the electrochemical stability window of the constituent materials in order to attain stable device operation. With this knowledge at hand, we have executed a number of more “applied science” studies, where we have used the acquired information from the basic-science studies for the rational design of improved devices. We have demonstrated LEC devices with significantly improved device performance, as exemplified by an orange-red device that emitted significant light (> 100 cd/m2) for more than one month of uninterrupted operation, and a yellow-green device that emitted significant light for 25 days at a low voltage of 4 V and at relatively high efficiency (6 lm/W). Finally, we have conceptualized and realized a solely solution-processed and metal-free LEC comprising graphene as the negative electrode and the conducting polymer PEDOT-PSS as the positive electrode. This type of devices represents a paradigm shift in the field of solid-state lighting as they demonstrate that it is possible to fabricate an entire light-emitting device from solution-processible and “green” carbon-based materials in a process that is akin to printing.
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