Controlled Migration of Lithium Cations by Diamine Bridges in Water-Processable Polymer-Based Solid-State Electrolyte Memory Layers for Organic Synaptic Transistors.

Synaptic transistors require sufficient retention (memory) performances of current signals to exactly mimic biological synapses. Ion migration has been proposed to achieve high retention characteristics but less attention has been paid to polymer-based solid-state electrolytes (SSEs) for organic synaptic transistors (OSTRs). Here, OSTRs with water-processable polymer-based SSEs, featuring ion migration-controllable molecular bridges, which are prepared by reactions of poly(4-styrenesulfonic acid) (PSSA), diethylenetriamine (DETA), and lithium hydroxide (LiOH) are demonstrated.

Influence of Acid-Doped Poly(ethylene imine) Interlayers on the Performance of Polymer:Nonfullerene Solar Cells.

This work reports that ultrathin polymeric films doped with organic acid molecules can act as an electron-transporting interfacial layer in polymer:nonfullerene solar cells. The polymeric interfacial layers, which consist of poly(ethylene imine) (PEI) doped with 3-hydroxypropane-1-sulfonic acid (HPSA) at various HPSA molar ratios, are introduced between transparent indium-tin oxide (ITO) electrodes and polymer:nonfullerene bulk heterojunction layers. The HPSA-doped PEI (PEI:HPSA) films are optically translucent in the wavelength range of ≈300-800 nm, while the acidity of PEI solutions reached ≈pH = 7 at HPSA = 30 mol%.

Water-Soluble Reactive Polymer Blends for Stable Memory Layers in Low-Voltage Nonvolatile Organic Memory Transistors with High Mobility and Data-Retention Characteristics.

Here low-voltage nonvolatile organic memory transistors, featuring high charge-carrier mobility and outstanding data-retention characteristics, by employing water-soluble reactive polymer blends as a gate-insulating memory layer are demonstrated. Blend films of poly(vinyl alcohol) (PVA) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) (PVA:PAMPSA) are prepared from their aqueous solutions with various molar ratios of PAMPSA (0-18 mol%) and thermally annealed at 70 and 110 °C. Organic field-effect transistors (OFETs) are fabricated by depositing poly(3-hexylthiophene) (P3HT) channel layers on the thermally treated PVA:PAMPSA films.

Performance and Stability of Polymer:Nonfullerene Solar Cells with 100 °C-Annealed Electron-Collecting Combination Layers.

Invited for this month's cover is the group of Youngkyoo Kim at the Kyungpook National University. The image shows the improved electron transfer by hybrid combination layers featuring peculiar morphology for better efficiency and stability in polymer solar cells. The Full Paper itself is available at 10.

Performance and Stability of Polymer : Nonfullerene Solar Cells with 100 °C-Annealed Electron-Collecting Combination Layers.

Inverted-type organic solar cells, fabricated with low-temperature-processed combination layers of hybrid electron-collecting buffer layers (ECBLs) consisting of zinc oxide (ZnO) and poly(2-ethyl-2-oxazoline) (PEOz) and additional PEOz interlayers, showed improved performance and stability. The ZnO : PEOz precursor films with various PEOz compositions (0-12 wt %) were prepared and thermally treated at 100 °C, leading to the ECBLs on which the PEOz interlayers were subsequently deposited before coating of polymer : nonfullerene bulk heterojunction layers. Results showed that the power conversion efficiency of solar cells reached approximately 9.

Persistent electrical energy generation from organic diodes under constant pressure: toward organic gravity nanogenerators.

Here it is demonstrated that electricity can be continuously generated by pressing organic diodes with the poly(3-hexylthiophene) (P3HT) layers which are sandwiched between indium-tin oxide and aluminum (Al) electrodes. The optimized single devices with the 150-nm-thick P3HT layers are able to generate 60 μV and 45 μA by pressing, while persistent voltage (50 μV) and current (45 μA) generations are achieved by continuous pressing for 7 days. The charge generation by pressing of organic diodes is supported by the current density-voltage and capacitance measurements, while the friction of pi-orbital electrons in the P3HT chains upon pressing is proposed for the mechanism of persistent electricity generation.

Short-Wave Infrared-Sensing Organic Phototransistors with a Triarylamine-Based Polymer Doped with a Lewis Acid-Type Small Molecule.

Here, we report that a triarylamine-based polymer, poly[,'-bis(4-butylphenyl)-,'-bis(phenyl)benzidine] (PolyTPD), is effectively doped with tris(pentafluorophenyl)borane (BCF) and the doping level is dependent on the molar ratio of BCF to PolyTPD (repeating unit). The doping reaction is performed at 25 °C at the solution states using chlorobenzene solvent by varying the BCF molar ratio up to 2.0.

Nano-crater morphology in hybrid electron-collecting buffer layers for high efficiency polymer:nonfullerene solar cells with enhanced stability.

Organic solar cells based on solution processes have strong advantages over conventional silicon solar cells due to the possible low-cost manufacturing of flexible large-area solar modules at low temperatures. However, the benefit of the low temperature process is diminished by a thermal annealing step at high temperatures (≥200 °C), which cannot be practically applied for typical plastic film substrates with a glass transition temperature lower than 200 °C, for inorganic charge-collecting buffer layers such as zinc oxide (ZnO) in high efficiency inverted-type organic solar cells. Here we demonstrate that novel hybrid electron-collecting buffer layers with a particular nano-crater morphology, which are prepared by a low-temperature (150 °C) thermal annealing process of ZnO precursor films containing poly(2-ethyl-2-oxazoline) (PEOz), can deliver a high efficiency (12.

Low-Voltage Organic Nonvolatile Memory Transistors with Water-Soluble Polymers Containing Thermally Induced Radical Dipoles.

A water-soluble acidic polymer, poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA), was applied as a gate-insulating layer for organic field-effect transistors (OFETs). Before depositing the poly(3-hexylthiophene) (P3HT) channel layers, the PAMPSA layers were subjected to thermal treatment at various temperatures from 140 to 230 °C. The OFET performance was greatly enhanced by thermal treatment between 140 and 170 °C, whereas it became very poor at higher temperatures (200-230 °C).

Multistacked Detectors with Transparency-Controlled Polymer:Nonfullerene Bulk Heterojunction Sensing Layers for Visible Light Communications.

Here, we report multistacked organic photodiodes (OPDs) for potential light-fidelity (Li-Fi) detectors in visible light communications. The multistacked detectors were fabricated by integrating semitransparent inverted-type OPDs with polymer:nonfullerene bulk heterojunction (BHJ) layers. The thickness of BHJ sensing layers in the inverted-type OPDs was controlled to 30, 60, and 100 nm for top, middle, and bottom cells in the multistacked detectors, respectively, while 30 nm thick metal (silver) electrodes were used for securing both electrical conductivity and optical transparency.

Enhanced superoxide sensitivity in organic field-effect transistor sensors by introducing nanoclay-polyphenol-polymer hybrid sensing channels.

Here we report that nanoclay-polyphenol-polymer hybrid sensing channels can greatly enhance the sensitivity for hazardous reactive oxygen species (ROS) in organic field-effect transistor (OFET) sensors. The hybrid layers were prepared by introducing nanoclay into the binary mixtures of poly(3-hexylthiophene) (P3HT) and rutin (a polyphenol) at various weight ratios. The presence of nanoclay improved the P3HT crystallinity in the hybrid films, which contributed to the increased drain current and well-maintained hole mobility even at the reduced amount of charge-transporting P3HT part.

Nanoscale Film Morphology and n-Type Digital Memory Characteristics of π-Conjugated Donor-Acceptor Alternating Copolymer Based on Thiophene and Thiadiazole Units.

Various molecular weight π-conjugated donor-acceptor polymers based on thiadiazole and thiophene units are investigated with respect to nanoscale film morphology and digital memory performance. Interestingly, all polymers reveal excellent n-type digital permanent memory characteristics, which are governed by the combination of Ohmic and trap-limited space charge limited conductions via a hopping process using thiadiazole and thiophene units as charge traps and stepping stones. The digital memory performance is significantly influenced by the film morphology details that vary with the polymer molecular weight as well as the film thickness.

High-Efficiency Polymer:Nonfullerene Solar Cells with Quaterthiophene-Containing Polyimide Interlayers.

Interfacial layers (interlayers) are one of the emerging approaches in organic solar cells with bulk heterojunction (BHJ) layers because the solar cell efficiency can be additionally improved by their presence. However, less attention is paid to the use of interlayers for polymer:nonfullerene solar cells, which have strong advantages over polymer:fullerene solar cells. In addition, most polymers used for the interlayers possess a low glass transition temperature ().

Ultrasensitive detection of hazardous reactive oxygen species using flexible organic transistors with polyphenol-embedded conjugated polymer sensing layers.

Here we report that superoxide, one of the hazardous reactive oxygen species (ROS), can be quickly detected by flexible organic field-effect transistors (OFETs) with the polyphenol-embedded conjugated polymer micro-channels. Rutin, one of the abundant polyphenols found in a variety of plants, was employed as a sensing molecule and embedded in the poly(3-hexylthiophene) (P3HT) matrix. The rutin-embedded P3HT layers showed randomly distributed micro-domains, which became bigger as the rutin content increased.

Pronounced Side Chain Effects in Triple Bond-Conjugated Polymers Containing Naphthalene Diimides for n-Channel Organic Field-Effect Transistors.

Three triple bond-conjugated naphthalene diimide (NDI) copolymers, poly{[ N, N'-bis(2-R)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]- alt-[(2,5-bis(2-R)-1,4-phenylene)bis(ethyn-2,1-diyl)]} (PNDIR-R), were synthesized via Sonogashira coupling polymerization with varying alkyl side chains at the nitrogen atoms of the imide ring and 2,5-positions of the 1,4-diethynylbenzene moiety. Considering their identical polymer backbone structures, the side chains were found to have a strong influence on the surface morphology/nanostructure, thus playing a critical role in charge-transporting properties of the three NDI-based copolymers. Among the polymers, the one with an octyldodecyl (OD) chain at the nitrogen atoms of imide ring and a hexadecyloxy (HO) chain at the 2,5-positions of 1,4-diethynylbenzene, P(NDIOD-HO), exhibited the highest electron mobility of 0.

Flexible Thermal Sensors Based on Organic Field-Effect Transistors with Polymeric Channel/Gate-Insulating and Light-Blocking Layers.

Here, we report flexible thermal sensors based on organic field-effect transistors (OFETs) that are fabricated using polymeric channel and gate-insulating layers on flexible polymer film substrates. Poly(3-hexylthiophene) and poly(methyl methacrylate) were used as the channel and gate-insulating layers, respectively, whereas indium-tin oxide-coated poly(ethylene naphthalate) films (thickness = 130 μm) were employed as the flexible substrates. Aluminum-coated polymer films were attached on top of the channel parts in the flexible OFETs to block any influence by light illumination.

Ultrasensitive Multi-Functional Flexible Sensors Based on Organic Field-Effect Transistors with Polymer-Dispersed Liquid Crystal Sensing Layers.

Ultrasensitive flexible sensors with multi-sensing functions are required for various applications in flexible electronics era. Here we demonstrate flexible polymer-dispersed liquid crystal (PDLC)-integrated-organic field-effect transistors (OFETs) (PDLC-i-OFETs), which sensitively respond to various stimulations including weak gas (air) flow, direct physical touch, light, and heat. The flexible PDLC-i-OFETs were fabricated by spin-coating the poly(methyl methacrylate) (PMMA)-dispersed 4,4'-pentyl-cyanobiphenyl (5CB) layers on the poly(3-hexylthiophene) (P3HT) channel layers of OFETs with 200 μm-thick poly(ethylene naphthalate) (PEN) substrates.

Efficient Deep Red Light-Sensing All-Polymer Phototransistors with p-type/n-type Conjugated Polymer Bulk Heterojunction Layers.

Here we demonstrate deep red light-sensing all-polymer phototransistors with bulk heterojunction layers of poly[4,8-bis[(2-ethylhexyl)-oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7) and poly[[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)] (P(NDI2OD-T2)). The device performances were investigated by varying the incident light intensity of the deep red light (675 nm), while the signal amplification capability was examined by changing the gate and drain voltages. The result showed that the present all-polymer phototransistors exhibited higher photoresponsivity (∼14 A/W) and better on/off photoswitching characteristics than the devices with the pristine polymers under illumination with the deep red light.

Influence of Weak Base Addition to Hole-Collecting Buffer Layers in Polymer:Fullerene Solar Cells.

We report the effect of weak base addition to acidic polymer hole-collecting layers in normal-type polymer:fullerene solar cells. Varying amounts of the weak base aniline (AN) were added to solutions of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The acidity of the aniline-added PEDOT:PSS solutions gradually decreased from pH = 1.

Strong Composition Effects in All-Polymer Phototransistors with Bulk Heterojunction Layers of p-type and n-type Conjugated Polymers.

We report the composition effect of polymeric sensing channel layers on the performance of all-polymer phototransistors featuring bulk heterojunction (BHJ) structure of electron-donating (p-type) and electron-accepting (n-type) polymers. As an n-type component, poly(3-hexylthiopehe-co-benzothiadiazole) end-capped with 4-hexylthiophene (THBT-4ht) was synthesized via two-step reactions. A well-studied conjugated polymer, poly(3-hexylthiophene) (P3HT), was employed as a p-type polymer.

Significant Stability Enhancement in High-Efficiency Polymer:Fullerene Bulk Heterojunction Solar Cells by Blocking Ultraviolet Photons from Solar Light.

Achievement of extremely high stability for inverted-type polymer:fullerene solar cells is reported, which have bulk heterojunction (BHJ) layers consisting of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) and [6,6]-phenyl-C71-butyric acid methyl ester (PCBM), by employing UV-cut filter (UCF) that is mounted on the front of glass substrates. The UCF can block most of UV photons below 403 nm at the expense of ≈20% reduction in the total intensity of solar light. Results show that the PTB7-Th:PCBM solar cell with UCF exhibits extremely slow decay in power conversion efficiency (PCE) but a rapidly decayed PCE is measured for the device without UCF.

Polymer Nanodot-Hybridized Alkyl Silicon Oxide Nanostructures for Organic Memory Transistors with Outstanding High-Temperature Operation Stability.

Organic memory devices (OMDs) are becoming more important as a core component in flexible electronics era because of their huge potentials for ultrathin, lightweight and flexible plastic memory modules. In particular, transistor-type OMDs (TOMDs) have been gradually spotlighted due to their structural advantages possessing both memory and driving functions in single devices. Although a variety of TOMDs have been developed by introducing various materials, less attention has been paid to the stable operation at high temperatures.

Acidity-Controlled Conducting Polymer Films for Organic Thermoelectric Devices with Horizontal and Vertical Architectures.

Organic thermoelectric devices (OTEDs) are recognized one of the next generation energy conversion platforms because of their huge potentials for securing electricity continuously from even tiny heat sources in our daily life. The advantage of OTEDs can be attributable to the design freedom in device shapes and the low-cost fabrication by employing solution coating processes at low temperatures. As one of the major OTE materials to date, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has been used, but no study has been yet carried out on its acidity control even though the acidic components in OTEDs can seriously affect the device performance upon operation.

Broadband pH-Sensing Organic Transistors with Polymeric Sensing Layers Featuring Liquid Crystal Microdomains Encapsulated by Di-Block Copolymer Chains.

We report broadband pH-sensing organic field-effect transistors (OFETs) with the polymer-dispersed liquid crystal (PDLC) sensing layers. The PDLC layers are prepared by spin-coating using ethanol solutions containing 4-cyano-4'-pentyl-biphenyl (5CB) and a diblock copolymer (PAA-b-PCBOA) that consists of LC-philic block [poly(4-cyano-biphenyl-4-oxyundecyl acrylate) (PCBOA)] and acrylic acid block [poly(acrylic acid) (PAA)]. The spin-coated sensing layers feature of 5CB microdomains (<5 μm) encapsulated by the PAA-b-PCBOA polymer chains.

Strong Photo-Amplification Effects in Flexible Organic Capacitors with Small Molecular Solid-State Electrolyte Layers Sandwiched between Photo-Sensitive Conjugated Polymer Nanolayers.

We demonstrate strong photo-amplification effects in flexible organic capacitors which consist of small molecular solid-state electrolyte layers sandwiched between light-sensitive conjugated polymer nanolayers. The small molecular electrolyte layers were prepared from aqueous solutions of tris(8-hydroxyquinoline-5-sulfonic acid) aluminum (ALQSA3), while poly(3-hexylthiophene) (P3HT) was employed as the light-sensitive polymer nanolayer that is spin-coated on the indium-tin oxide (ITO)-coated poly(ethylene terephthalate) (PET) film substrates. The resulting capacitors feature a multilayer device structure of PET/ITO/P3HT/ALQSA3/P3HT/ITO/PET, which were mechanically robust due to good adhesion between the ALQSA3 layers and the P3HT nanolayers.