Research

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16 pages, 4335 KiB

Open AccessArticle

Nanopiezoelectric Devices for Energy Generation Based on ZnO Nanorods/Flexible-Conjugated Copolymer Hybrids Using All Wet-Coating Processes

by Yu-Ping Lee, Chieh-Chuan Lin, Chih-Chung Hsiao, Po-An Chou, Yao-Yi Cheng, Chih-Chen Hsieh and Chi-An Dai

Micromachines 2020, 11(1), 14; https://doi.org/10.3390/mi11010014 - 20 Dec 2019

Cited by 8 | Viewed by 2298

Abstract

In this study, nanopiezoelectric devices based on ZnO nanorod array/conducting polymers are fabricated for wearable power generation application. To replace the inorganic rigid indium-tin oxide (ITO) conducting coating commonly used in the nanogenerator devices, a series of flexible polyaniline-based conducting copolymers underlying the [...] Read more.

In this study, nanopiezoelectric devices based on ZnO nanorod array/conducting polymers are fabricated for wearable power generation application. To replace the inorganic rigid indium-tin oxide (ITO) conducting coating commonly used in the nanogenerator devices, a series of flexible polyaniline-based conducting copolymers underlying the perpendicularly-oriented ZnO nanorod arrays has been synthesized with improved electric conductivity by the copolymerization of aniline and 3,4-ethylenedioxythiophene (EDOT) monomers in order to optimize the piezoelectric current collection efficiency of the devices. It is found that significantly higher conductivity can be obtained by small addition of EDOT monomer into aniline monomer solution using an in-situ oxidative polymerization method for the synthesis of the copolymer coatings. The highest conductivity of aniline-rich copolymer is 65 S/cm, which is 2.5 times higher than that for homopolymer polyaniline coating. Subsequently, perpendicularly-oriented ZnO nanorod arrays are fabricated on the polyaniline-based copolymer substrates via a ZnO nanoparticle seeded hydrothermal fabrication process. The surface morphology, crystallinity, orientation, and crystal size of the synthesized ZnO nanorod arrays are fully examined with various synthesis parameters for copolymer coatings with different monomer compositions. It is found that piezoelectric current generated from the devices is at least five times better for the device with improved electric conductivity of the copolymer and the dense formation of ZnO nanorod arrays on the coating. Therefore, these results demonstrate the advantage of using flexible π-conjugated copolymer films with enhanced conductivity to further improve piezoelectric performance for future wearable energy harvesting application based on all wet chemical coating processes. Full article

(This article belongs to the Special Issue Organic Electronic Devices)

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9 pages, 4898 KiB

Open AccessArticle

Solvent-Dependent Electrical Characteristics and Mechanical Stability of Flexible Organic Ferroelectric Field-Effect Transistors

by Do-Kyung Kim, Hyeonju Lee, Xue Zhang, Jin-Hyuk Bae and Jaehoon Park

Micromachines 2019, 10(11), 727; https://doi.org/10.3390/mi10110727 - 28 Oct 2019

Cited by 5 | Viewed by 2821

Abstract

Flexible organic ferroelectric field-effect transistors (Fe-FETs) have attracted attention for next-generation memory applications. A fundamental understanding of the electrical properties and mechanical stability of transistors is a prerequisite to realizing practical flexible electronics. Here, we demonstrate the solvent-dependent electrical characteristics and mechanical stability [...] Read more.

Flexible organic ferroelectric field-effect transistors (Fe-FETs) have attracted attention for next-generation memory applications. A fundamental understanding of the electrical properties and mechanical stability of transistors is a prerequisite to realizing practical flexible electronics. Here, we demonstrate the solvent-dependent electrical characteristics and mechanical stability of flexible Fe-FETs. Poly(vinylidene fluoride-trifluoro-ethylene) (P(VDF-TrFE)) based Fe-FETs were fabricated by using dimethylformamide (DMF) and methyl ethyl ketone (MEK) solvents on a polyimide substrate. P(VDF-TrFE) from DMF formed a smoother surface than a surface from MEK; the surface property greatly affected the electrical properties and mechanical stability of the devices. Larger hysteresis and higher mobility were obtained from Fe-FET using DMF compared to those characteristics from using MEK. Furthermore, Fe-FET using DMF showed lower degradation of on-current and mobility under repetitive mechanical stress than an MEK-based Fe-FET, due to its excellent semiconductor-insulator interface. These results will guide appropriate solvent selection and contribute to the improvement of flexible Fe-FET electrical properties and mechanical stability in the next generation of memory devices. Full article

(This article belongs to the Special Issue Organic Electronic Devices)

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10 pages, 3486 KiB

Open AccessArticle

One-Step Coating Processed Phototransistors Enabled by Phase Separation of Semiconductor and Dielectric Blend Film

by Lin Gao, Sihui Hou, Zijun Wang, Zhan Gao, Xinge Yu and Junsheng Yu

Micromachines 2019, 10(11), 716; https://doi.org/10.3390/mi10110716 - 24 Oct 2019

Cited by 5 | Viewed by 3221

Abstract

Fabrication of organic thin-film transistors (OTFTs) via high throughput solution process routes have attracted extensive attention. Herein, we report a simple one-step coating method for vertical phase separation of the poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(methyl methacrylate) (PMMA) blends as semiconducting and dielectric layers in [...] Read more.

Fabrication of organic thin-film transistors (OTFTs) via high throughput solution process routes have attracted extensive attention. Herein, we report a simple one-step coating method for vertical phase separation of the poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(methyl methacrylate) (PMMA) blends as semiconducting and dielectric layers in OTFTs. These OTFTs can be used as phototransistors for ultraviolet (UV) light detection, where the phototransistors exhibited great photosensitivity of 597.6 mA/W and detectivity of 4.25 × 10¹⁰ Jones under 1 mW/cm² UV light intensity. Studies of the electrical properties in these phototransistors suggested that optimized P3HT contents in the blend film can facilitate the improvement of film morphology, and therefore form optimized vertical phase separation of the PMMA and P3HT. These results indicate that the simple one-step fabrication method creates possibilities for realizing high throughput phototransistors with great photosensitivity. Full article

(This article belongs to the Special Issue Organic Electronic Devices)

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10 pages, 5021 KiB

Open AccessArticle

Improved Memory Properties of Graphene Oxide-Based Organic Memory Transistors

by Amjad Al-shawi, Maysoon Alias, Paul Sayers and Mohammed Fadhil Mabrook

Micromachines 2019, 10(10), 643; https://doi.org/10.3390/mi10100643 - 25 Sep 2019

Cited by 5 | Viewed by 2473

Abstract

To investigate the behaviour of the organic memory transistors, graphene oxide (GO) was utilized as the floating gate in 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)-based organic memory transistors. A cross-linked, off-centre spin-coated and ozone-treated poly(methyl methacrylate) (cPMMA) was used as the insulating layer. High mobility and negligible [...] Read more.

To investigate the behaviour of the organic memory transistors, graphene oxide (GO) was utilized as the floating gate in 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)-based organic memory transistors. A cross-linked, off-centre spin-coated and ozone-treated poly(methyl methacrylate) (cPMMA) was used as the insulating layer. High mobility and negligible hysteresis with very clear transistor behaviour were observed for the control transistors. On the other hand, memory transistors exhibited clear large hysteresis which is increased with increasing programming voltage. The shifts in the threshold voltage of the transfer characteristics as well as the hysteresis in the output characteristics were attributed to the charging and discharging of the floating gate. The counter-clockwise direction of hysteresis indicates that the process of charging and discharging the floating gate take place through the semiconductor/insulator interface. A clear shift in the threshold voltage was observed when different voltage pulses were applied to the gate. The non-volatile behaviour of the memory transistors was investigated in terms of charge retention. The memory transistors exhibited a large memory window (~30 V), and high charge density of (9.15 × 10¹¹ cm⁻²). Full article

(This article belongs to the Special Issue Organic Electronic Devices)

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8 pages, 2354 KiB

Open AccessArticle

Reducing the Nano-Scale Aggregation of Perylene Diimide Based Acceptor by Conjugating a Bridge with a Large Volume

by Jun-Yi Chen, Xu-Dong Xia and Jicheng Zhang

Micromachines 2019, 10(10), 640; https://doi.org/10.3390/mi10100640 - 24 Sep 2019

Cited by 2 | Viewed by 2275

Abstract

A novel perylene diimide (PDI) based acceptor P-PDI was synthesized by attaching a phenyl bridge to two octyloxy side chains. With two large volume side chains, the planarity of P-PDI was significantly reduced, leading to weak nano-aggregation of the PDI groups between the [...] Read more.

A novel perylene diimide (PDI) based acceptor P-PDI was synthesized by attaching a phenyl bridge to two octyloxy side chains. With two large volume side chains, the planarity of P-PDI was significantly reduced, leading to weak nano-aggregation of the PDI groups between the different acceptor molecules. Differential scanning calorimetry (DSC) experiments also revealed that P-PDI was amorphous, and demonstrating the aggregation of P-PDI was successfully suppressed. When blended with PTB7-Th to fabricate a polymer solar cell, a power conversation efficiency (PCE) of 2.21% was achieved, demonstrating that a conjugated bridge with a big volume side chain could significantly reduce the nano-scale aggregation of PDI based acceptor materials, which provides a new strategy to synthesize high efficiency acceptors based on PDI. Full article

(This article belongs to the Special Issue Organic Electronic Devices)

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8 pages, 1226 KiB

Open AccessArticle

Magneto-Electroluminescence in ITO/MEH-PPV:PEO:LiCF₃SO₃/Al Polymer Light-Emitting Electrochemical Cells

by Mingpeng Zhu, Xueting Yuan and Gang Ni

Micromachines 2019, 10(8), 546; https://doi.org/10.3390/mi10080546 - 17 Aug 2019

Cited by 3 | Viewed by 3983

Abstract

Magnetic field effects (MFE) have been extensively studied in organic light emitting diodes because of their potential application in organic spintronics devices. However, only a few studies on MFE in organic light-emitting electrochemical cells (LEC) have been reported. In this paper, magnetic field [...] Read more.

Magnetic field effects (MFE) have been extensively studied in organic light emitting diodes because of their potential application in organic spintronics devices. However, only a few studies on MFE in organic light-emitting electrochemical cells (LEC) have been reported. In this paper, magnetic field effects on the electroluminescence of an LEC device with the structure of ITO/MEH-PPV:PEO:LiCF₃SO₃/Al were studied at various temperatures. The luminance–current–voltage curves of the device shows the typical bi-polar characteristics of LECs; positive magnetic electroluminescence (MEL) was observed with a value of about 2.5% (B = 42 mT, 250 K), showing a Lorentzian line shape. With a decrease in temperature, the MEL value and the threshold voltage increased accordingly, below the possible mechanism is discussed. Full article

(This article belongs to the Special Issue Organic Electronic Devices)

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11 pages, 5211 KiB

Open AccessArticle

High Brightness Organic Light-Emitting Diodes with Capillary-Welded Hybrid Diameter Silver Nanowire/Graphene Layers as Electrodes

by Jianhua Zhang, Yiru Li, Bo Wang, Huaying Hu, Bin Wei and Lianqiao Yang

Micromachines 2019, 10(8), 517; https://doi.org/10.3390/mi10080517 - 03 Aug 2019

Cited by 9 | Viewed by 2976

Abstract

The development of silver nanowire electrodes is always limited due to some disadvantages, such as roughness, oxidative properties, and other disadvantages. In this research, a capillary-welded silver nanowire/graphene composite film was used as an electrode for organic light-emitting diode (OLED) devices. As an [...] Read more.

The development of silver nanowire electrodes is always limited due to some disadvantages, such as roughness, oxidative properties, and other disadvantages. In this research, a capillary-welded silver nanowire/graphene composite film was used as an electrode for organic light-emitting diode (OLED) devices. As an encapsulation layer, graphene reduced the surface roughness and the oxidation probability of silver nanowires. The composite electrode showed an excellent transmittance of 91.5% with low sheet resistant of 26.4 ohm/sq. The devices with the silver nanowire/graphene composite electrode emitted green electroluminescence at 516 nm, and the turn-on voltage was about 3.8 V. The maximum brightness was 50810 cd/cm², which is higher than the indium tin oxide-based (ITO-based) devices with the same configuration. Finally, it was proved that the silver nanowire/graphene composite electrodes possessed better heat dissipation than the ITO-based ones under energization. In summary, it means that this novel silver nanowires/graphene electrode has great potential in OLED device applications. Full article

(This article belongs to the Special Issue Organic Electronic Devices)

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9 pages, 1455 KiB

Open AccessArticle

Study of Hole-Transporter-Free Perovskite Solar Cells based on Fully Printable Components

by Camellia Raminafshar, Dimitrios Raptis, Mohammad Reza Mohammadi and Panagiotis Lianos

Micromachines 2019, 10(4), 266; https://doi.org/10.3390/mi10040266 - 20 Apr 2019

Cited by 8 | Viewed by 3542

Abstract

Hole-transporter-free perovskite solar cells carrying a carbon back contact electrode provide the possibility of making full printable low cost and stable devices, even though their efficiency is substantially lower than those made in the standard configuration. The present work searched for simple and [...] Read more.

Hole-transporter-free perovskite solar cells carrying a carbon back contact electrode provide the possibility of making full printable low cost and stable devices, even though their efficiency is substantially lower than those made in the standard configuration. The present work searched for simple and easy routes for constructing such devices, demonstrating that organic components do enhance device efficiency but only to a level that is not worth the trouble nor the cost. Devices based on a triple mesoporous layer of titania/zirconia/carbon with perovskite infiltration gave an efficiency of 10.7%. After 180 days of storing under ambient conditions, a small loss of efficiency has been observed for a cell made in June, in spite of the fact that in going from June to December, a large increase of the ambient humidity took place, thus verifying the protective effect that the carbon electrode is providing. The addition of spiro-OMeTAD to the hole-transporter-free device resulted in increasing the efficiency by about 10%, a change which is appreciated to be of low importance given the cost of this material. This increase mainly derived from an increase in the current. Devices of different sizes have been constructed by screen printing, using home-made pastes for all the components making the cell scaffold, i.e., for titania, zirconia, and carbon layers. Full article

(This article belongs to the Special Issue Organic Electronic Devices)

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Review

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30 pages, 7313 KiB

Open AccessReview

Spin Injection and Transport in Organic Materials

by Qipeng Tian and Shijie Xie

Micromachines 2019, 10(9), 596; https://doi.org/10.3390/mi10090596 - 10 Sep 2019

Cited by 4 | Viewed by 3848

Abstract

This review introduces some important spin phenomena of organic molecules and solids and their devices: Organic spin injection and transport, organic spin valves, organic magnetic field effects, organic excited ferromagnetism, organic spin currents, etc. We summarize the experimental and theoretical progress of organic [...] Read more.

This review introduces some important spin phenomena of organic molecules and solids and their devices: Organic spin injection and transport, organic spin valves, organic magnetic field effects, organic excited ferromagnetism, organic spin currents, etc. We summarize the experimental and theoretical progress of organic spintronics in recent years and give prospects. Full article

(This article belongs to the Special Issue Organic Electronic Devices)

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