Materials

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9 pages, 2450 KiB

Open AccessEditor’s ChoiceCommunication

Effect of Gate Bias Stress on the Electrical Characteristics of Ferroelectric Oxide Thin-Film Transistors with Poly(Vinylidenefluoride-Trifluoroethylene)

by Bon-Seong Gu, Eun-Seo Park, Jin-Hyuk Kwon and Min-Hoi Kim

Materials 2023, 16(6), 2285; https://doi.org/10.3390/ma16062285 - 12 Mar 2023

Viewed by 1629

Abstract

We investigated the effect of gate bias stress (GBS) on the electrical characteristics of ferroelectric oxide thin-film transistors (FeOxTFTs) with poly(vinylidenefluoride-trifluoroethylene). Generally, conventional oxide thin-film transistors (OxTFTs) with dielectric gate insulators exhibit a small negative shift under negative gate bias stress (NBS) and [...] Read more.

We investigated the effect of gate bias stress (GBS) on the electrical characteristics of ferroelectric oxide thin-film transistors (FeOxTFTs) with poly(vinylidenefluoride-trifluoroethylene). Generally, conventional oxide thin-film transistors (OxTFTs) with dielectric gate insulators exhibit a small negative shift under negative gate bias stress (NBS) and a large positive shift under positive gate bias stress (PBS) in transfer characteristic curves. In contrast, the FeOxTFTs show a small positive shift and a large negative shift under NBS and PBS, respectively. It was confirmed that sufficient changes in the electrical characteristics are obtained by 10 min NBS and PBS. The changed electrical characteristics such as threshold voltage shift, memory on- and memory off-current were maintained for more than 168 h after NBS and 24 h after PBS. It is deduced that, since the dipole alignment of the ferroelectric layer is maximized during GBS, these changes in electrical properties are caused by the remnant dipole moments still being retained during the gate sweep. The memory on- and memory off-current are controlled by GBS and the best on/off current ratio at 10⁷ was obtained after NBS. By repeatedly alternating NBS and PBS, the electrical characteristics were reversibly changed. Our results provide the scientific and technological basis for the development of stability and performance optimization of FeOxTFTs. Full article

(This article belongs to the Special Issue Soft Materials and Optical Devices)

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8 pages, 2202 KiB

Open AccessEditor’s ChoiceArticle

Deformable Photonic Crystals Based on Chiral Liquid Crystals with Thermal-Mediative Shape Memory Effect

by Min-Seok Park, Kitae Kim, Young-Joo Lee, Jun-Hee Na and Se-Um Kim

Materials 2023, 16(1), 35; https://doi.org/10.3390/ma16010035 - 21 Dec 2022

Cited by 1 | Viewed by 1350

Abstract

We propose a deformable photonic crystal that exhibits the thermal-mediative shape memory effect. The chiral liquid crystalline polymeric scaffold, which produces the structural colors from a helical twist of the liquid crystal director, is prepared through phase-stabilization of a reactive mesogen in a [...] Read more.

We propose a deformable photonic crystal that exhibits the thermal-mediative shape memory effect. The chiral liquid crystalline polymeric scaffold, which produces the structural colors from a helical twist of the liquid crystal director, is prepared through phase-stabilization of a reactive mesogen in a small molecular chiral liquid crystal (CLC), polymerization, and removal of the CLC. The prepolymer of polyurethane acrylate (PUA) is then infiltrated in the prepared scaffold and subsequently photo-polymerized to form a CLC-PUA composite film. Upon compression, this film shows the blue shift of the structural color and retains this color-shift as released from compression. As the temperature increases, the color is recovered to a pristine state. The concept proposed in this study will be useful for designing mechanochromic soft materials. Full article

(This article belongs to the Special Issue Soft Materials and Optical Devices)

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21 pages, 3908 KiB

Open AccessEditor’s ChoiceArticle

Experimental and Computational Studies on Bio-Inspired Flavylium Salts as Sensitizers for Dye-Sensitized Solar Cells

by Iulia Păușescu, Anamaria Todea, Diana-Maria Dreavă, Tania Boboescu, Bianca Pațcan, Larisa Pațcan, Daiana Albulescu, Valentin Badea, Francisc Peter, Róbert Tőtős, Daniel Ursu, Lorant Szolga and Mihai Medeleanu

Materials 2022, 15(19), 6985; https://doi.org/10.3390/ma15196985 - 08 Oct 2022

Cited by 1 | Viewed by 2519

Abstract

Six new bio-inspired flavylium salts were synthesized and investigated by a combined computational and experimental study for dye-sensitized solar cell applications. The compounds were characterized by FT–IR, UV–Vis, NMR spectroscopy, and LC–MS spectrometry techniques. The pH-dependent photochromic properties of the flavylium dyes were [...] Read more.

Six new bio-inspired flavylium salts were synthesized and investigated by a combined computational and experimental study for dye-sensitized solar cell applications. The compounds were characterized by FT–IR, UV–Vis, NMR spectroscopy, and LC–MS spectrometry techniques. The pH-dependent photochromic properties of the flavylium dyes were investigated through a UV–Vis spectroscopy study and revealed that they follow the same network of chemical reactions as anthocyanins upon pH changes. The structural and electronic properties of the dyes were investigated using density functional theory (DFT) and time-dependent density functional theory (TD–DFT). Geometry optimization calculation revealed that all dyes, regardless of the specie, flavylium cations or quinoidal bases, present a planar geometry. The photovoltaic performances of the dyes, in both flavylium and quinoidal base forms, were evaluated by the HOMO and LUMO energies and by calculating the light-harvesting efficiencies, the free energy change of electron injection, and the free energy change regeneration. The MO analysis showed that all dyes can inject electrons into the conduction band of the TiO₂ upon excitation and that the redox couple can regenerate the oxidized dyes. The results obtained for the free energy change of electron injection suggest that the quinoidal bases should inject electrons into the semiconductor more efficiently than the flavylium cations. The values for the free energy change regeneration showed that the redox electrolyte can easily regenerate all dyes. Dipole moment analysis was also performed. DSSCs based on the dyes, in both flavylium and quinoidal base forms, were assembled, and their photovoltaic performances were evaluated by measuring the open-circuit voltage, the short circuit current density, the fill factor, and the energy conversion efficiency. Results obtained by both experimental and computational studies showed that the overall performances of the DSSCs with the quinoidal forms were better than those obtained with the flavylium cations dyes. Full article

(This article belongs to the Special Issue Soft Materials and Optical Devices)

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11 pages, 3320 KiB

Open AccessArticle

Fabrication of Color Glass with High Light Transmittance by Pearlescent Pigments and Optical Adhesive

by Hyeon-Sik Ahn, Akpeko Gasonoo, Seong-Min Lim, Jae-Hyun Lee and Yoonseuk Choi

Materials 2022, 15(7), 2627; https://doi.org/10.3390/ma15072627 - 02 Apr 2022

Cited by 6 | Viewed by 2098

Abstract

In this study, we propose a solution process for realizing colored glass for building integrated photovoltaic (BIPV) systems by spin coating a color solution composed of pearlescent pigments mixed in a Norland Optical Adhesive (NOA) matrix. Color solutions are made from mixing pearlescent [...] Read more.

In this study, we propose a solution process for realizing colored glass for building integrated photovoltaic (BIPV) systems by spin coating a color solution composed of pearlescent pigments mixed in a Norland Optical Adhesive (NOA) matrix. Color solutions are made from mixing pearlescent pigments in NOA63. Compared to a physical vapor deposition process, color coatings are achieved by spin coating in a relatively simple and inexpensive process at room temperature. The optical properties can be easily controlled by adjusting the spin coating speed and the concentration of the pearlescent pigments. The produced colored glass achieved a high transmittance of 85% or more in the visible wavelength range, except for the wavelength spectrum exhibiting the maximum reflectance. In addition, we propose a one-step lamination process of colored glass on a solar cell by leveraging on the adhesive property of the NOA matrix. This eliminates the cost and process of additional ethylene vinyl acetate (EVA) layer or other materials used in the conventional lamination process. The colored glass produced through this study has stability that does not change its properties over time. Therefore, it is expected to be applied to the BIPV solar module market where aesthetics and energy efficiency are required. Full article

(This article belongs to the Special Issue Soft Materials and Optical Devices)

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11 pages, 2637 KiB

Open AccessArticle

Fabrication of Multi-Layer Metal Oxides Structure for Colored Glass

by Akpeko Gasonoo, Hyeon-Sik Ahn, Eun-Jeong Jang, Min-Hoi Kim, Jin Seog Gwag, Jae-Hyun Lee and Yoonseuk Choi

Materials 2021, 14(9), 2437; https://doi.org/10.3390/ma14092437 - 07 May 2021

Cited by 8 | Viewed by 2103

Abstract

This study proposes front colored glass for building integrated photovoltaic (BIPV) systems based on multi-layered derivatives of glass/MoO₃/Al₂O₃ with a process technology developed to realize it. Molybdenum oxide (MoO₃) and aluminum oxide (Al₂O₃ [...] Read more.

This study proposes front colored glass for building integrated photovoltaic (BIPV) systems based on multi-layered derivatives of glass/MoO₃/Al₂O₃ with a process technology developed to realize it. Molybdenum oxide (MoO₃) and aluminum oxide (Al₂O₃) layers are selected as suitable candidates to achieve thin multi-layer color films, owing to the large difference in their refractive indices. We first investigated from a simulation based on wave optics that the glass/MoO₃/Al₂O₃ multi-layer type offers more color design freedom and a cheaper fabrication process when compared to the glass/Al₂O₃/MoO₃ multi-layer type. Based on the simulation, bright blue and green were primarily fabricated on glass. It is further demonstrated that brighter colors, such as yellow and pink, can be achieved secondarily with glass/MoO₃/Al₂O₃/MoO₃ due to enhanced multi-interfacial reflections. The fabricated color glasses showed the desired optical properties with a maximum transmittance exceeding 80%. This technology exhibits promising potential in commercial BIPV system applications. Full article

(This article belongs to the Special Issue Soft Materials and Optical Devices)

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8 pages, 2202 KiB

Open AccessArticle

Improving of Sensitivity of PbS Quantum Dot Based SWIR Photodetector Using P3HT

by Kyeong-Ho Seo, Jaewon Jang, In Man Kang and Jin-Hyuk Bae

Materials 2021, 14(6), 1488; https://doi.org/10.3390/ma14061488 - 18 Mar 2021

Cited by 4 | Viewed by 3444

Abstract

In this study, we improved the photosensitivity of the lead sulfide quantum dot (PbS QD)-based shortwave infrared (SWIR: 1.0–2.5 μm) photodetector by blending poly(3-hexylthiophene-2,5-diyl) (P3HT) with PbS QD. The PbS QD used for SWIR photoactive layer showed an absorption peak at 1410 nm. [...] Read more.

In this study, we improved the photosensitivity of the lead sulfide quantum dot (PbS QD)-based shortwave infrared (SWIR: 1.0–2.5 μm) photodetector by blending poly(3-hexylthiophene-2,5-diyl) (P3HT) with PbS QD. The PbS QD used for SWIR photoactive layer showed an absorption peak at 1410 nm. In addition, by using zinc oxide nanoparticles (ZnO NPs) as an interlayer, we obtained the stable current characteristics of our device. To confirm the effectiveness of P3HT on the PbS QD-based SWIR photodetector, we compared the electrical characteristics of a PbS QD-based device with a hybrid P3HT:PbS QD-based device. In the reverse bias region, the current on/off ratio of the PbS QD-based device was 1.3, whereas the on/off ratio of the hybrid P3HT:PbS QD-based device was 2.9; 2.2 times higher than the PbS QD-based device. At −1 V, the on/off ratio of the PbS QD-based device was 1.3 and the on/off ratio of the hybrid P3HT:PbS QD-based device was 3.4; 2.6 times higher than the PbS QD-based device. The fabricated P3HT:PbS QD-based device had the highest on/off ratio when −1 V voltage was applied. Full article

(This article belongs to the Special Issue Soft Materials and Optical Devices)

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10 pages, 3190 KiB

Open AccessEditor’s ChoiceArticle

Carbon Dot/Naphthalimide Based Ratiometric Fluorescence Biosensor for Hyaluronidase Detection

by Pushap Raj, Seon-yeong Lee and Tae Yoon Lee

Materials 2021, 14(5), 1313; https://doi.org/10.3390/ma14051313 - 09 Mar 2021

Cited by 12 | Viewed by 2865

Abstract

Bladder cancer is the leading cause of death in patients with genitourinary cancer. An elevated level of hyaluronidase (HAase) was found in bladder cancer, which acts as an important biomarker for the early diagnosis of bladder cancer. Hence, there is a need to [...] Read more.

Bladder cancer is the leading cause of death in patients with genitourinary cancer. An elevated level of hyaluronidase (HAase) was found in bladder cancer, which acts as an important biomarker for the early diagnosis of bladder cancer. Hence, there is a need to develop a simple enzymatic assay for the early recognition of HAase. Herein, we report a simple, sensitive, and ratiometric fluorescence assay for HAase detection under physiological conditions. The fluorescence assay was constructed by the adsorption of cationic carbon dots and positively charged naphthalimide on negatively charged hyaluronic acid and the development of a Förster resonance energy transfer (FRET) mechanism from carbon dots to a naphthalimide fluorophores. The hyaluronidase enzyme cleaves the hyaluronic acid in this assay, and breaking down the FRET mechanism induces ratiometric changes. A detection limit of 0.09 U/mL was achieved, which is less than the HAase level found in normal human body fluids. Moreover, this assay may be used for diagnosing HAase-related diseases. Full article

(This article belongs to the Special Issue Soft Materials and Optical Devices)

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7 pages, 1869 KiB

Open AccessArticle

Effect of Buffer Layer Capacitance on the Electrical Characteristics of Ferroelectric Polymer Capacitors and Field Effect Transistors

by Eun-Kyung Noh, Amos Boampong, Yu Konno, Yuji Shibasaki, Jae-Hyun Lee, Yoonseuk Choi and Min-Hoi Kim

Materials 2021, 14(5), 1276; https://doi.org/10.3390/ma14051276 - 08 Mar 2021

Cited by 4 | Viewed by 1882

Abstract

We demonstrated the effect of a buffer layer on the electrical characteristics of ferroelectric polymer capacitors and field-effect transistors. Various polymer materials with a dielectric constant between 2 and 42 were used to form buffer layers with a similar thicknesses, but with different [...] Read more.

We demonstrated the effect of a buffer layer on the electrical characteristics of ferroelectric polymer capacitors and field-effect transistors. Various polymer materials with a dielectric constant between 2 and 42 were used to form buffer layers with a similar thicknesses, but with different capacitances. In order to evaluate the characteristics of the ferroelectrics with a buffer layer, the polarization–voltage characteristics of the capacitor, the transfer characteristics, and the retention characteristics of the transistors were investigated. As the capacitance of the buffer layer increased, high remnant polarization (P_r), high hysteresis, and long retention times were observed. Exceptionally, when poly(methylmethacrylate) and rigid poly(aryl ether) (poly(9,9-bis(4-hydroxyphenyl)fluorene-co-decafluorobiphenyl)) were used as the buffer layer, P_r had a value close to 0 in the dynamic measurement polarization–voltage (P–V) characteristic, but the quasi-static measurement transfer characteristic and the static measurement retention characteristic showed relatively high hysteresis and long retention times. Our study provides a scientific and technical basis for the design of ferroelectric memory and neuromorphic devices. Full article

(This article belongs to the Special Issue Soft Materials and Optical Devices)

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11 pages, 3708 KiB

Open AccessArticle

Design Optimization of Reconfigurable Liquid Crystal Patch Antenna

by Dowon Kim, Kitae Kim, Hogyeong Kim, Moonyoung Choi and Jun-Hee Na

Materials 2021, 14(4), 932; https://doi.org/10.3390/ma14040932 - 16 Feb 2021

Cited by 8 | Viewed by 3396

Abstract

In various fields such as the 5G antenna system and satellite communication system, there is a growing demand to develop a smart antenna with a frequency selective or beamforming function within a limited space. While antennas utilizing mechanical, electronic, and material characteristics are [...] Read more.

In various fields such as the 5G antenna system and satellite communication system, there is a growing demand to develop a smart antenna with a frequency selective or beamforming function within a limited space. While antennas utilizing mechanical, electronic, and material characteristics are being studied, a method of having tunable frequency characteristics by applying a liquid crystal material with dielectric anisotropy to a planar patch antenna is proposed. In resonance mode, the design method for using only the minimum amount of expensive liquid crystals is systematically arranged while maximizing the amount of change in the operating frequency of the antenna by considering the electric field distribution on the surface of the patch antenna. Furthermore, to increase the dielectric anisotropy of the liquid crystal, the liquid crystal must be aligned. Simultaneously, in cases where the cell gap of the liquid crystal exceeds 100 μm, the alignment force is weakened. While compensating for this shortcoming, securing the radiation characteristics of the antenna is proposed, and simulations are performed. Full article

(This article belongs to the Special Issue Soft Materials and Optical Devices)

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