| 1. |
- Tewari, Amit, et al.
(författare)
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Low-cost dielectric sheets for large-area floor sensing applications
- 2022
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Ingår i: Flexible and Printed Electronics. - : Institute of Physics. - 2058-8585. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- Sensitivity response is a critical parameter that decides the domain of dielectric materials to be implemented as piezocapacitive sensors for low- or high-pressure sensing applications. Here, we have clarified the sensitivity response behavior of three low-cost dielectric materials, two biodegradable paperboards, and one acoustic polymeric foam. The devices are fabricated in the form of a metal-insulator-metal structure, and the capacitive response of the devices is measured using the charge extraction by linearly increasing voltage technique. The sensitivity response curve (ΔC/C o vs. pressure) reveals that the paperboard materials are sensitive enough to detect low-pressure regimes (45 kPa), whereas the acoustic foam is quite promising for high-pressure monitoring (above 150 kPa). Using a multiplexer circuit, we demonstrated the sensitivity response via 2 by 2 matrix structure both as a steady-state and transient response. Our results show that the passive matrix structure interference between different pixels can be minimized after increasing the spacing between electrodes strip. Finally, a full-scale demonstrator (dimension 120 cm × 400 cm) with a 2 × 8 matrix structure laminated under floor tiling has been demonstrated. We show how such a floor sensor utilizing the low-cost substrates can be used to recognize single-stepping, walking, and falling.
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| 2. |
- Wilken, Sebastian, et al.
(författare)
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Experimentally Calibrated Kinetic Monte Carlo Model Reproduces Organic Solar Cell Current–Voltage Curve
- 2020
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Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 4:6
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Tidskriftsartikel (refereegranskat)abstract
- Kinetic Monte Carlo (KMC) simulations are a powerful tool to study the dynamics of charge carriers in organic photovoltaics. However, the key characteristic of any photovoltaic device, its current–voltage (J–V) curve under solar illumination, has proven challenging to simulate using KMC. The main challenges arise from the presence of injecting contacts and the importance of charge recombination when the internal electric field is low, i.e., close to open-circuit conditions. Herein, an experimentally calibrated KMC model is presented that can fully predict the J–V curve of a disordered organic solar cell. It is shown that it is crucial to make experimentally justified assumptions on the injection barriers, the blend morphology, and the kinetics of the charge transfer state involved in geminate and nongeminate recombination. All of these properties are independently calibrated using charge extraction, electron microscopy, and transient absorption measurements, respectively. Clear evidence is provided that the conclusions drawn from microscopic and transient KMC modeling are indeed relevant for real operating organic solar cell devices.
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| 3. |
- Zabihipour, Marzieh, 1985-
(författare)
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Organic Electrochemical Transistors for Printed Digital Circuits
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organic electronics enables cost-effective production of flexible electronic devices with high throughput and easy processing compared to the conventional electronics. Organic electronics, therefore, has the potential to realize various innovative applications on a large scale, for example, flexible displays, smart windows, solar cells, electronic skin and implantable medical devices.Many of the materials employed in the field of organic electronics can be processed from chemical solutions. This allows for making various types of inks and hence the possibility to use the traditional high-volume printing methods such as screen printing, inkjet printing and gravure printing for fabricating organic electronic devices on different surfaces. Screen printing has advantages over the other methods in terms of the range of ink viscosity, resolution, and controllable thickness of dry ink film.For various applications envisioned for an integration of printed organic electronics with other technology platforms, a prolonged lifetime and low power consumption are desired. This requires an optimized design of the electronic components and circuits so that they can operate at reduced voltages to guarantee both the long lifetime and the low power consumption. This thesis focuses on designing fully screen printed vertically stacked organic electrochemical transistors (OECTs) and OECT-based circuits operating at low supply voltages and at the same time delivering high gain and low power consumption with long lifetime. The OECTs and OECT-based circuits employ poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) as the organic polymer in their channel. The multi-layered OECTs have a small footprint with a high manufacturing yield and performance uniformity across the printed area, making them suitable for complex printed circuits. Furthermore, various inverter designs based on the reliable and reproducible OECTs are developed and explored to target circuits that can perform at relatively low supply voltages, yet offering improved performance.
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| 4. |
- Zhang, Qilun, 1992-
(författare)
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Materials and interfaces for sustainable organic solar cells
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Photovoltaics, the apparatus utilizing green solar power to generate electricity, is one of the efficient measures to the continuously increasing energy demand and exacerbated carbon emission of the human civilization. As a candidate with the potential of providing the cheapest and greenest form of electricity, organic solar cells (OSCs) received tremendous scientific interest, resulting in a significant power conversion efficiency (PCE) boosting to above 19% recently. Despite the impressive achievements in PCE, it’s alone not enough for the commercialization of OSCs. Sufficient lifetime and scalability at competitive cost are necessary as well. A better understanding of the interface energetic properties and materials electronic structures in the multilayer stacked OSCs are needed to improve the inherent instability of the devices. In addition, exploration of the sustainable and low-cost materials for OSCs are crucial. In this thesis, we carefully investigated dipole-induced energy level matching at the OSC interfaces, and the oxygen/water caused electronic structure evolution of the OSC materials via various of spectroscopic characterizations, and introduced natural wood-based materials to achieve highly efficient and stable OSCs.We employed ultraviolet photoelectron spectroscopy (UPS) to investigate the interface energetic properties of a commercially available cathode interface layer (CIL) material polyvinylpyrrolidone (PVP) in OSCs and proposed a "double dipole" model to explain the work function modification properties of PVP on several substrates. Then we used the large-area compatible immersion method to obtain the ultrathin PVP layer on the ITO substrate, the fabricated OSCs have a comparable efficiency to the traditional Zinc Oxide (ZnO) CIL based devices. We further use photoelectron spectroscopy (PES) to investigate the electronic structures of advanced OSC materials, i.e., PM6 and Y6. To better understand the degradation mechanism caused by water and oxygen in these materials, the electronic structures of the materials were in-situ characterized in near-ambient pressure with controllable water and oxygen dosing. We carefully analyzed the evolution of the PES spectra during the water and oxygen dosing, and unveiled that oxygen affected backbone sulfur in PM6 and a weak interaction between cyano groups in Y6 with water. Furthermore, the enhanced stability of the Y6 was observed in the blend films as the electronic structures in the PES spectra, which matched the device results of PM6 and Y6 based OSCs that the blend photoactive layers show better stability in air atmosphere than bilayer.Lastly, we presented the application feasibility of the natural wood-based materials in state of art OSCs to achieve better stability and lower cost. We firstly introduced an insulating polymer of natural betulin into the active layer, following the “filler strategy”, resulting in an improved open circuit voltage (Voc) in donor-acceptor-insulator ternary OSCs. We attribute this improvement to the decreased trap-assisted recombination, however, we simultaneously found reduced charge collection in the devices caused by the penetration of the filler materials at the bottom, forming insulator interface to block the charge transfer. The present work expands the range of filler materials in OSCs to include biomass, with the aim of developing highly efficient, environmentally friendly, and cost-effective OSCs. We further extended the utilization of natural wood-based materials to cathode interface layer (CIL). Kraft lignin (KL), the most abundant natural source of aromatic material constituents, has potential compatibility to various of traditional CIL materials, owing to the chemical activity of phenolic functionalities. In this work, we successfully combined the traditional CIL materials, i.e., PFN-Br and bathocuproine (BCP), with large ratio (30%-50% in weight ratio) of industrial solvent fractionated KL, obtained binary CILs with tuneable WF. The binary CILs with suitable KL ratio worked well in OSCs, exhibited equivalent or even higher efficiency to the traditional CILs. In addition, the combination of KL and BCP significantly enhanced the stability of the devices, which mainly ascribed to the protection from KL to block the reaction between BCP and fused-ring electron acceptors.The author hopes the findings in this thesis can contribute to the industrialization of OSCs, especially from the aspect of the sustainability, cost and stability.
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