Trivalent Ionic Molecular Bridges as Efficient Charge-Trapping Method for All-Solid-State Organic Synaptic Transistors toward Neuromorphic Signal Processing Applications.

Achieving high retention of memory state is crucial in artificial synapse devices for neuromorphic computing systems. Of various memorizing methods, a charge-trapping method provides fast response times when it comes to the smallest size of electrons. Here, for the first time, it is demonstrated that trivalent molecular bridges with three ionic bond sites in the polymeric films can efficiently trap electrons in the organic synaptic transistors (OSTRs).

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.

A polymer library enables the rapid identification of a highly scalable and efficient donor material for organic solar cells.

The dramatic improvement of the PCE (power conversion efficiency) of organic photovoltaic devices in the past few years has been driven by the development of new polymer donor materials and non-fullerene acceptors (NFAs). In the design of such materials synthetic scalability is often not considered, and hence complicated synthetic protocols are typical for high-performing materials. Here we report an approach to readily introduce a variety of solubilizing groups into a benzo[][1,2,5]thiadiazole acceptor comonomer.

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.

Preface to the Special Issue of ChemSusChem on Advanced Organic Solar Cells.

Organic solar cells have garnered much interest as an Earth-abundant and low-energy-production renewable energy source. In their Editorial to the Special Issue on Advanced Organic Solar Cells, Guest Editors Christoph Brabec, Martin Heeney, Youngkyoo Kim, and Christine Luscombe introduce this exciting field and discuss some of the Special Issue's contents.

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.

Significant Performance Improvement in n-Channel Organic Field-Effect Transistors with C :C Co-Crystals Induced by Poly(2-ethyl-2-oxazoline) Nanodots.

Solution-processed organic field-effect transistors (OFETs) have attracted great interest due to their potential as logic devices for bendable and flexible electronics. In relation to n-channel structures, soluble fullerene semiconductors have been widely studied. However, they have not yet met the essential requirements for commercialization, primarily because of low charge carrier mobility, immature large-scale fabrication processes, and insufficient long-term operational stability.

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.

Near-Infrared Organic Phototransistors with Polymeric Channel/Dielectric/Sensing Triple Layers.

A new type of near-infrared (NIR)-sensing organic phototransistor (OPTR) was designed and fabricated by employing a channel/dielectric/sensing (CDS) triple layer structure. The CDS structures were prepared by inserting poly(methyl methacrylate) (PMMA) dielectric layers (DLs) between poly(3-hexylthiophene) (P3HT) channel layers and poly[{2,5-bis-(2-octyldodecyl)-3,6-bis-(thien-2-yl)-pyrrolo[3,4-c]pyrrole-1,4-diyl}-co-{2,2'-(2,1,3-benzothiadiazole)-5,5'-diyl}] (PODTPPD-BT) top sensing layers. Two different thicknesses of PMMA DLs (20 nm and 50 nm) were applied to understand the effect of DL thickness on the sensing performance of devices.

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.