Table of contents

Organic electronics such as organic field-effect transistors (OFET), organic light-emitting diodes (OLED), and organic photovoltaics (OPV) have flourished over the last three decades, largely due to the development of new conjugated materials. Their designs have evolved through incremental modification and stepwise inspiration by researchers; however, a complete survey of the large molecular space is experimentally intractable. Machine learning (ML), based on the rapidly growing field of artificial intelligence technology, offers high throughput material exploration that is more efficient than high-cost quantum chemical calculations. This review describes the present status and perspective of ML-based development (materials informatics) of organic electronics. Although the complexity of OFET, OLED, and OPV makes revealing their structure-property relationships difficult, a cooperative approach incorporating virtual ML, human consideration, and fast experimental screening may help to navigate growth and development in the organic electronics field.

Surface imprinted polymers (SIPs) are versatile receptors in bioanalytical applications for the selective detection of cells and microorganisms such as bacteria. One of the synthesis routes is the so-called stamping method in which template bacteria are pressed mechanically into a thin, gel-like polyurethane layer, which is then cured in the presence of the templates to create cell-specific binding pockets on the polymer. The present work focusses on two specific steps of the imprinting protocol: first, we evaluate the sedimentation of two different groups of bacteria, Escherichia coli and Escherichia blattae, on silicone stamps with respect to the resulting surface coverage, which is a key factor for the efficiency of the imprinting process. Second, we analyse the temperature dependence of the thermal- and dielectric properties of polyurethane during curing by dielectric- and pyroelectric spectroscopy. This provides information for improved curing protocols and on the stability of SIP materials at elevated temperatures.

Vertical structure of ensemble molecular electronic junction is a widely used platform for investigating the electrical properties of molecular monolayers. Direct metal deposition on the molecular layer, however, causes the shorted circuit problem in the most junctions. One of the methods to avoid this problem is transferring pre-made electrodes on the molecular layer. This article reviews the large-area molecular electronic junctions fabricated in such a way and discusses about their fabrication process, device yield, electrical properties, and applications. The earlier part of this article introduces the molecular junctions with metal (e.g. Au) electrodes transferred in various methods. In the later part, the electrical characteristics and functionalities of the molecular junctions adapting the graphene electrodes are reviewed.

The stereoregularity effect on carrier mobility of stereoregular poly(N-vinylcarbazole) (PVK) was studied using metal–insulator–semiconductor charge extraction by the linearly increasing voltage technique. The hole mobility of stereoregular PVK thin film was dependent upon the stereoregularity (mm) and was enhanced to be 4.02 × 10⁻⁶ cm² V⁻¹ s⁻¹ at mm = 94%, which was 4.8 times higher than that at mm = 50%. Furthermore, the activation energy depending on the stereoregularity of PVK was evaluated to be from 118 meV (mm = 50%) to 111 meV (mm = 94%) in faint variation. The enhanced carrier transport in the stereoregular PVK thin film was discussed by taking the stereoregularity involved with the intramolecular interaction through the carbazole substituents into consideration.

Solvent vapor annealing (SVA) was examined for poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14) thin films as the activate layer of top-contact, bottom-gate transistors. SVA with chlorobenzene vapor was performed on different types of PBTTT-C14 films; pristine films on SiO₂, thermally-annealed films on SiO₂, and thermally-annealed films on alkylsilane-modified SiO₂. Solvent vapors penetrated into the PBTTT-C14 films and caused some similar effects as conventional post-thermal annealing, such as reduced molecular lamellae spacing and increased field-effect mobility. Additionally, the hole mobility of the thermally-annealed film on alkylsilane-modified SiO₂ was increased by SVA with relatively shorter duration, even without any obvious shifts in lattice spacing and optical absorption bands of the films. This means that SVA only for the film surface and the upper part of the organic active layer may be effective for improving electrode contact interfaces in top-contact transistors. The roles of SVA for tailoring structures and field-effect carrier transport in PBTTT-C14 films are considered.

The formation and stability of a benzenedithiol monolayer on a Si substrate with a Au layer have been investigated to obtain a monolayer having high thermal stability as compared to that formed by use of a benzenethiol derivative. The monolayer was formed by immersing into an ethanol solution of 1,2-benzenedithiol (BDT). The work function of BDT-monolayer surface was measured for the investigation. The association constant for the adsorption of the molecules was estimated from the change of the work function. The subsequent annealing of the substrate with a BDT-monolayer at 500 K or lower did not lead to the change of the work function. Substrates with a BDT-monolayer were also examined using X-ray photoelectron spectroscopy (XPS). The work function and XPS spectra measured indicated that a BDT-monolayer formed on a Au surface is stable to annealing at temperatures up to about 473 K.

Homogeneous alignment of a π-conjugated polymer, poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C16), was obtained by bar-coating method in thin film. The macroscopic direction of the main chain orientation, that tended to be parallel or perpendicular to the coating direction, strongly depended on the coating speed. The optical and electrical anisotropies of the bar-coated thin film were demonstrated. By observing the surface morphology, it is revealed that the coating speed affected the polymeric aggregation. The molecular orientation mechanism through the polymeric aggregation in the coating process was discussed.

Uniaxially orientated thin film of phthalocyanine with bulky tert-butyl substituents (t-BuPcH₂) was fabricated by bar-coating method. The thin film exhibited high dichroic ratio of more than 50 in the polarized absorption. Molecular packing structure of t-BuPcH₂ in the thin film was suggested by using the results of XRD measurements, in which the molecular plane of t-BuPcH₂ was determined to be perpendicular to the substrate and bar-sweep direction. In addition, the X-ray rocking curve measurements demonstrated that t-BuPcH₂ possessed highly molecular orientation in the thin film fabricated by bar-coating method.

Complex modulus spectra of organic field-effect transistors (OFETs) with electrode overlap regions were investigated both experimentally and theoretically. Complex modulus spectra in a poly(3-hexylthiophene-2,5-diyl) (P3HT) FET were measured using an impedance analyzer. An equivalent-circuit of OFETs with the overlap between gate and source/drain electrodes was proposed to interpret the experimentally-obtained complex modulus spectra. The complex modulus spectra calculated from the equivalent circuit were successfully fitted to the experimentally-obtained spectra of P3HT FETs. It is shown that the dielectric properties of the gate insulator, the field-effect mobility of the organic semiconductor, and the contact resistance are obtained by means of the fitting of the theoretically-obtained modulus spectra to the experimentally-obtained spectra.

Microneedle crystals of 1,4-bis-(4-methylstyryl)benzene (DSB-4Me) and amorphous microdots of bis (N,N-di-p-tolylamino-p-styryl)benzene (DADSB) are fabricated by using mask-shadowing and conventional vapor deposition techniques. By interaction between π-conjugated electronic chains and ionic lattice of a KCl crystal substrate, DSB-4Me molecules grow into needle crystals epitaxially orienting in four directions making ±60° against [110]_KCl and [−110]_KCl. As for DADSB, self-assembly into microdots by heating the KCl substrate at 180 °C during deposition is attributed to the impact of bulky peripheral groups in DADSB and surface migration of the deposited molecules. Moreover, while amplified spontaneous emission is observed above an excitation threshold of 362 μJ cm⁻² in the DSB-4Me microneedle crystals, a lower threshold whispering-gallery mode lasing is observed above 37 μJ cm⁻² for DADSB microdots owing to the higher waveguide quality.

The stability of phosphonic acid self-assembled monolayers (SAMs) in water was studied on aluminum surfaces. The aim was to understand the stability of SAMs under the practical conditions that are relevant to various applications. After exposing the as-prepared alkyl- and fluoroalkyl-SAM surfaces to water at 40 °C for 2 h, the contact angle decreased from more than 100° to less than 20°. Thermally annealed SAMs showed larger water contact angles after exposing to water, indicating that the desorption of the molecules was depressed.

Mixed monolayers consisting of 4-fluorobenzenethiolate and 1-octadecanethiolate on Au surfaces were formed by immersing in an ethanol solution of 4-fluorobenzenethiol (FBT), and subsequently by immersing in that of 1-octadecanethiol (ODT). To obtain systematically a mixed monolayer, the formation of FBT- and ODT-monolayers was investigated with respect to the reaction time and concentration of the solution. The monolayer formed on a Au surface was evaluated based on the work function, the water contact angle, and the X-ray photoelectron spectroscopy (XPS) spectra measured. The XPS measurement of substrates prepared for formation of a mixed monolayer exhibited F 1s and C 1s spectra supporting the presence of a mixed monolayer consisting of 4-fluorobenezenethiolate and 1-octadecanethiolate.

Many organic conducting materials are represented by the charge transfer (CT) complexes of tetrathiafulvalene (TTF) and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), which show high conductivity at room temperature. CT complexes of TTF and TCNQ each form columnar structures in crystals that enable the application of CT complexes in the formation of one-dimensional nanostructures such as nanowires and nanorods. Crown ethers units can also be used to support the preparation of self-assembled one-dimensional structures. In this study, we reported that the structures and electrical properties composed of TTF derivative (TTF-ER) and CT complexes composed of (TTF-ER)(TCNQ), (TTF-ER)(F2TCNQ) and (TTF-ER)(F4TCNQ). TTF-ER and the CT complexes organized one-dimensional structures on solid substrate, and in particular, TTF-ER formed high oriented nano-branched structures. In UV–vis and IR spectra, the CT complexes has conductivity similar to that of semiconductors, the electrical conductivities of (TTF-ER)(F2TCNQ) and (TTF-ER)(F4TCNQ) at room temperature were found to be 1.2 × 10⁻⁵ and 1.4 × 10⁻⁵ S cm⁻¹, respectively.

Quantitative analyses of photodegradation for three fluorene-based photovoltaic polymers, poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (APFO3), polyfluorene (PFO), and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), were conducted to understand the molecular origin of photostability for polymers. The Fourier transform infrared spectra of the polymer thin films varied with irradiating white light at 100 mW cm⁻² irrespective of their molecular architectures. The absorption peaks corresponding to alkyl side chains in the fluorene unit decreased, whereas those for polymers that did not comprise carbonyl groups increased. This spectral variation indicates that alkyl side chains in the fluorene unit decompose when the molecular structure of fluorene changes to that of fluorenone. The reaction rate constant of the formation of C=O bonds for APFO3 was 1.64 × 10⁻⁵ s⁻¹, lower than those for PFO (7.59 × 10⁻⁵ s⁻¹) and F8BT (2.64 × 10⁻⁵ s⁻¹), under light irradiation at 30 °C. The photostability of the polymers was improved by designing a donor–acceptor type molecular architecture incorporating photostable electron-deficient benzothiadiazole units with photo-unstable fluorene units.

Two types of naphthalenediimide derivatives, N,N'-bis(benzyl)naphthalenediimide (Bzl-NDI) and N,N'-bis(p-vinylbenzyl)naphthalenediimide (PVB-NDI), were vapor-deposited either on a bare aluminum or an aluminum modified with a self-assembled monolayer (SAM) of (3-mercaptopropyl)trimethoxysilane. The deposition on the SAM-modified surface was achieved under UV irradiation to enhance thiol-ene reaction of the SAM with vinyl groups of the deposited molecules. The films of Bzl-NDI gradually crystallized, while PVB-NDI formed stable amorphous films. Electron-only devices were prepared with combinations of Bzl- and PVB-NDIs with bare and the SAM-modified aluminum cathodes. PVB-NDI was less conductive than Bzl-NDI due to the amorphous nature of the film. The SAM modification on the cathode was effective to increase the electron current of the PVB-NDI device, whereas the SAM modification did not increase the current of the Bzl-NDI device. The implication is that the thiol-terminated SAM can bind with PVB-NDI that has the vinyl group, leading to an improvement of the organic/cathode interface.

In this study, we fabricated flexible organic field-effect transistors (OFETs) (bottom-gate and top-contact architecture) based on the blend film composed of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) as a π-conjugated small-molecule semiconductor and polystyrene (PS) as a polymer insulator. Blend solutions including both the TIPS pentacene and PS molecules were electrosprayed onto bottom-gate electrodes which were patterned on polyethylene naphthalate films. The devices exhibited superior electrical characteristics due to well-defined vertical phase separation between the TIPS pentacene crystalline layer (top) and PS insulator (bottom). This study will contribute to a facile one-step printing process to produce high-performance flexible OFETs.

We show the first experimental evidence that submicron particles (diameter: approximately 400 nm) using 5,5'-di(4-biphenylyl)-2,2'-bithiophene (BP2T) prepared by a miniemulsion technique are effective active media for vertical microcavities. Selected area electron diffraction patterns confirm that crystalline BP2T submicron particles are obtained. In a distributed Bragg reflector-Au microcavity with BP2T submicron particles embedded in a poly(vinyl alcohol) (PVA) matrix (thickness: ∼780 nm), gain-narrowed emissions are observed at the 0–3 emission band of BP2T above an excitation density of 107 μJ cm⁻². The light amplification of 0–3 photoluminescence band obtained in the present study demonstrates that the PVA film containing the BP2T submicron particles is useful as an active medium for microcavities.

Herein, we report the thermophysical properties of dichloro-[2,2]-paracyclophane (the parylene C dimer) under vacuum. The parylene C dimer is the raw material used to prepare parylene C, a thin film known for its useful dielectric and barrier properties. In order to investigate the first step in the synthesis of parylene C by chemical vapor deposition, the sublimation, evaporation, and melting behavior of the parylene C dimer was examined by simultaneous thermogravimetry/differential thermal analysis (TG–DTA) under vacuum and at atmospheric pressure. The evaporation onset temperatures, saturation vapor pressures, and the phase-transition temperatures of the parylene C dimer were quantified by TG–DTA at various pressures. The evaporation and sublimation temperature easily decreased by increasing the level of vacuum, while the melting temperature was independent of the external pressure. Our results led to the construction of a pressure–temperature phase diagram.

A mesh structure (graphene nanomesh) was fabricated by Ullmann coupling of hexabromotriphenylene (HBTP) on Au (111) and Cu (111) surfaces. While HBTP molecules deposited on the Au (111) surface formed a hexagonally packed array at room temperature, after annealing at 373 K the mesh structure was formed in which the distance between nanoholes was approximately 0.8 nm. It agreed with the distance between nanoholes in the mesh structure model that was expected to be formed by HBTP molecules. On the other hand, HBTP molecules deposited on the Cu (111) surface at room temperature formed random filament-like aggregates and subsequent annealing did not change the structure. HBTP deposited on the Cu (111) surface at 473 K also formed the mesh structure, which had less irregularly bound molecules and vacancies than that on the Au (111) surface. The Cu (111) surface heated at 473 K during molecular deposition, on which molecular arrangement and orientations were reversely changed during coupling reaction, was better for forming the high quality mesh structure than the Au (111) surface.

Herein, we present a vapor film deposition method for fabricating polycrystalline films of a thiophene/phenylene co-oligomer. The polycrystalline film has comparable physical and optical characteristics, e.g. an amplified spontaneous emission, to those of the single-crystal phase as the film consists of tiny single crystals with a grain size of 5–20 μm. Meanwhile, in situ FET results illustrate the dominant unipolar p-type characteristics with a hole mobility of 0.025 cm² V⁻¹ s⁻¹, higher than the conventional physically deposited films owing to the standing molecular orientation.

To investigate the influence of asymmetric intermolecular interactions of phenyl-C₆₁-butyric acid methyl ester (PCBM), the behaviors of C₆₀ and PCBM molecules deposited on the same Au (111) surface were observed by scanning tunneling microscopy under ultra-high vacuum conditions. After annealing, the system formed polygonal islands, the peripheries of which were occupied by PCBM molecules having their functional groups directed outside of the island, whereas the inside was composed of hexagonally packed C₆₀ molecules. Such exclusion of PCBM from the C₆₀ domain is attributed to asymmetric intermolecular interactions of PCBM: namely, the cage of PCBM has an affinity for C₆₀ and the cages of other PCBM owing to van der Waals interactions. However, the functional groups of PCBM prevented C₆₀ from attaching. The PCBM molecules at the periphery pinned the island's edges along the stripes of a herringbone reconstruction region owing to the weak affinity of the tail for the fcc region to determine the shape of the islands.

The effect of the metal-insulator-semiconductor (MIS) structure with magnesium fluoride (MgF₂) was investigated for the charge extraction by the linearly increasing voltage method using metal-insulator-semiconductor structure (MIS-CELIV). Hole mobilities of N,N´-bis(naphthalen-1-yl)-N,N´-bis(phenyl)-benzidine (NPB) films were measured for devices with a MgF₂ insulator above or below the NPB film. Both devices yielded ideal MIS-CELIV signals and hole mobilities, which are consistent with those for conventional Si/SiO₂ devices. The validity of the estimated mobilities were discussed by analyzing the amount of extracted charges affected by the surface traps on MgF₂. The usage of an evaporable insulating material can allow the free placement of the insulating layer; enabling configurations where the underlying layer does not falsely influence the organic layer.

Among the large number of π-conjugated compounds, thiophene/phenylene co-oligomers have been one of the promising candidates for both optically pumped light amplification media and light emission media in electroluminescence devices owing to their high thermal stability, high photoluminescence (PL) quantum yield and high carrier mobility. Of these, the single-crystal state of 5,5''-bis(4-biphenylyl)−2,2':5',2''-terthiophene (BP3T), which has been frequently used as an active medium in organic light-emitting transistor devices, indicates an unusual light amplification process in its PL spectra. Herein, we explain two insights about the indication of a cooperative light amplification process in BP3T single crystals under optical pumping. The first one is excitation beam area dependence for the nonlinear amplification threshold in PL spectra at room temperature, which has previously been carried out at 12 K. The second one is time-delayed amplified emission in various excitation stripe lengths.

The effect of silver nanoplate (AgPL) on the singlet exciton fission (SF) of rubrene (Rub) was verified by examining the magnetic field effects (MFEs) on the SF of Rub through measuring magnetic field dependence of fluorescence intensity of Rub in two thick Rub polymer-composite films in the absence and the presence of AgPL. The fluorescence intensity of Rub in the Rub-AgPL polymer-composite film was larger than that in the Rub polymer-composite film. The enhancement (1.4 times) must be caused by strong electric fields due to localized surface plasmon resonance (LSPR) of the embedded AgPL near the Rub in polymer matrix. The magnitude of the MFEs in the Rub-AgPL polymer-composite film was almost same as those in the Rub polymer-composite film. These results strongly indicate that the efficiency of SF was enhanced by the LSPR due to the embedded AgPL into the polymer matrix in the Rub-AgPL polymer-composite film.

Effects of silver nanoplate (AgPL) and magnetic field on photon upconversion based on sensitized triplet–triplet annihilation (PUC-TTA) were examined in the system of platinum(II) octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA), when AgPLs were incorporated into polymer thin films containing PtOEP and DPA. In the presence of AgPL, the PUC emission intensity increased as compared with that in the absence of AgPL. The result is most likely attributable to the localized surface plasmon resonance of AgPL. On the other hand, in the absence of AgPL, the PUC emission intensity decreased in the presence of magnetic field, while in the presence of AgPL, the PUC emission intensity increased drastically in the presence of magnetic field. The synergetic effect of AgPL and magnetic field on the PUC emission intensity in PUC-TTA was observed for the first time.

Dielectric dispersions in the homogeneous (${\varepsilon }_{\perp }$) and the homeotropic (${\varepsilon }_{\parallel }$) aligned cells in the nematic phase of PCPB/MBBA mixtures have been measured in the frequency range between 100 Hz and 1 MHz. The Cole–Cole formula accounting for DC conduction has been found to reproduce dielectric dispersions well in all of the mixtures. The crossover frequency ${f}_{{\rm{c}}}$ monotonously increases with increasing the MBBA concentration. It has been also found that the strengths of dielectric anisotropy both in the high and the low frequency regions are enhanced by adding of MBBA at least below 50 mol%. The dielectric anisotropy in the present system has been discussed qualitatively on the basis of the Landau-type free energy density.

The dispersibility improvement of graphite for water is achieved by using microwave irradiation in a hydrogen peroxide aqueous solution without catalyst and a strong oxidation reagent. The dispersibility is improved by introducing oxygen functional groups by chemical reaction graphite and hydroxyl radicals. However, the chemical reaction occurs only at the graphite edge which is different from other chemical methods with strong oxidant. As a result, the sample maintains a slightly expanded graphite structure. The obtained samples show higher conductivity than that of raw graphite in spite of a non-reduction. The conductivity increases with increasing microwave irradiation time and the maximum value was reached at about 140 S mm⁻¹. This result is explained by high crystallinity and low defect density. Therefore, the microwave-irradiated graphite oxide is expected as a printable conductive carbon material.

We report LED properties in perovskite semiconductor and thiophene/phenylene co-oligomer (TPCO) double heterostructures. Perovskite semiconductors were formed by using a simple solution process, the "cast-capping method", on substrates with TPCOs. The electroluminescence was quenched rapidly, but it recovered to nearly its initial states. Under pulsed operation within 3 V, the device had rather long durability. We compared the LED properties with those of TPCO LEDs. Ion migrations and/or light-emitting electrochemical cell operations were strongly suggested in the perovskite/TPCO LEDs.

In this research, the thermal stability of pentacene-based organic FETs (OFETs) was investigated utilizing an amorphous rubrene (α-rubrene) passivation layer. Pentacene channel layers with a thickness of 10 nm were deposited at RT and at 100 °C. The influence of the α-rubrene passivation layer, which was in situ deposited on the pentacene at RT, was examined. The stability of the electrical characteristics and the crystallinity were compared with those after heating to 100 °C in air. For the pentacene deposited without an α-rubrene passivation layer, device performance was remarkably degraded after the heating process. On the other hand, the device characteristics of pentacene-based OFETs with an α-rubrene passivation layer were found to be stable after heating. Furthermore, the α-rubrene passivation layer stabilized the crystallinity of the pentacene layers during the heating process.

Inverted organic light-emitting diodes (inverted OLEDs) require electron injection to an organic semiconductor from a transparent oxide electrode. Polyethylenimine ethoxylated (PEIE) has attracted considerable attention as an electron injection material. An injection mechanism has been suggested; however, the barrier height of electron injection has not been determined. In this paper, we present the experimental values for the electron injection barrier height at the transparent oxide electrode/PEIE/organic semiconductor interface. Electron-only devices, consisting of indium-tin-oxide (ITO)/PEIE/tris(8-hydroxyquinolinato) aluminum (Alq₃)/Al, are fabricated. The temperature dependence of the current–voltage curves is measured corresponding to the electron injection of the ITO/PEIE/Alq₃ interface. The current–voltage curves are found to be independent of the measurement temperature, which is explained by the tunneling model. The tunneling injection barriers height are calculated, and the experimental injection barrier height will be important for the development of inverted OLED devices.

Organic–inorganic hybrid lead halide perovskite nanocrystals (PeNCs) have received great attention as a light source for perovskite LEDs (PeLEDs) owing to the superior optical properties. However, PeNCs typically use octylamine (OAm) as capping ligands which have insulating properties. Exploring a desirable short alkylamine instead of OAm is required for the improvement of PeLEDs. Here, as one of the strategies to solve this issue, the effects of alkylamine chain length for optical properties of PeNCs and PeLED characteristics are investigated. Pentylamine is an optimal short alkylamine and precipitate luminescent PeNCs with high PLQY values of 90%. Importantly, pentylamine maintains a relatively high PLQY of 48% after spin-coating, due to the durability pentylamine has to ethyl acetate as a washing solvent. PeNCs capped with pentylamine also demonstrate an external quantum efficiency of over 1% with luminance of over 2000 cd cm⁻², indicating that pentylamine has the potential to overcome the insulator properties of PeNC thin film.

Semiconducting and insulating polymer blend transistors have been studied to improve their air stability and create stretchable devices for skin electronics. Electron-transporting (or n-type) semiconducting polymers have significant problems regarding their device stability and performances. In this study, we tried to solve the stability issue of the n-type organic thin-film transistors (OTFTs). In order to extend the device lifetime, polyacrylonitrile (PAN) was introduced as an additive to the typical n-type naphthalenediimide (NDI)-based polymer, namely, P(NDI2T-OD) or N2200. PAN was well mixed with P(NDI2T-OD) to produce homogeneous solutions in chloroform/chlorobenzene mixtures when the PAN proportion was less than 5 wt%. The stability of the OTFTs stored in air was evaluated based on the electron mobility μ_e, threshold voltage V_th, and I_on/I_off ratio. Adding a small amount of PAN can significantly improve the stability and μ_e values of the OTFTs probably due to the gas barrier and water trapping characteristics of the PAN.

The surface potentials of 1-hexadecanethiol [HDT: CH₃(CH₂)₁₅SH] and 1-hexadecanol [HDO : CH₃(CH₂)₁₅OH] self-assembled monolayers (SAMs) were measured with reference to a 1-hexadecene [HD : CH₃(CH₂)₁₃CH=CH₂] SAM using Kelvin probe force microscopy. These molecules possess the same hydrocarbon chain length but vary in the covalent bond formed with the silicon substrate (Si–S, Si–O and Si–C). Micropatterned SAMs were used to eliminate the effects of surface potential variation of the probes. Surface potential contrasts against the reference HD SAM were measured to be −72 mV and −45 mV for HDT and HDO SAM respectively. These results agree qualitatively with surface potentials of the SAMs predicted from dipole moments of the molecules grafted to silicon as estimated by Molecular Orbital Package semi-empirical computations. The surface potential is found to be a result of dipoles formed by the adsorbed molecule as well as the interfacial bond between molecule and substrate.

In this study, a platinum (Pt) leaf was introduced as a counter electrode (CE) with thickness of 100 nm in dye-sensitized solar cells (DSCs). Fundamental characteristics were investigated and compared with Pt leaf, Pt plate, and sputtered-Pt as the CEs. The power conversion efficiencies of DSCs with a Pt leaf as the CEs were as high as 4.78%, which is higher to those of DSCs with Pt plate and sputtered-Pt as the CEs (4.11% and 4.40%, respectively). In contrast to other CEs, Pt leaf features a large surface area. This implies that Pt leaf serves as an active CE and can be a good candidate for DSCs.

We fabricated multilayered inverted polymer-based LEDs (iPLEDs) consisting of several types of solution-processed electron injection layer (EIL)/F8BT [green light emitting polymer (LEP)] or polyfluorene-based blue LEP (PFO)/TFB (hole-transporting layer)/MoO₃/Ag structures. We compared the electrical properties of hybrid iPLEDs with solution-processed hybrid EILs deposited at low temperature (<120 °C) consisting of ZnO/polyethyleneimine (PEI), PEI/tantalum oxide nanosheet (TaO-NS), and PEI/TaO-NS/TmPyPB multilayers. The combination of PEI dipole and ultra-thin TaO-NS (∼1 nm) layers improved the EL efficiency and operating voltages owing to the energy level shift of ∼1 eV and the effective hole blocking at the ITO/TaO-NS/LEP interface. However, a considerable barrier height of >0.5 eV still existed at the TaO-NS/PFO interface. The insertion of electron-transporting small molecules between the TaO-NS and PFO layer effectively reduced the electron injection barrier height and electron transport properties of the multilayered iPLEDs resulting in improved EQE and operating voltage for the blue-light iPLEDs.

We report the performances of planar organic photovoltaics (OPVs) using a low bandgap polymer (PTB7) as a donor (D) and three perylenetetracarboxylic diimide derivatives with different substituents on the nitrogen atoms, phenylethyl (PEPTC), (4-fluorophenyl)ethyl (4FPEPTC), and (4-methoxyphenyl)ethyl (4MeOPEPTC) as acceptors (A). These acceptors with different dipolar moments at the end group are expected to exhibit different interactions with the underlying PTB7 layer. An anomalous low open-circuit voltage (V_oc) in the OPV with PTB7/4FPEPTC was obtained due to the orientation of dipolar moments at the D/A interfaces induced by the orientation of 4FPEPTC with 4-fluorophenyl groups. On the other hand, although the terminal 4-methoxyphenyl group in 4MeOPEPTC has a dipole moment in the opposite direction to the terminal 4-fluorophenyl group in 4FPEPTC, the expected large V_oc was not obtained in the OPV with PTB7/4MeOPEPTC due to the disorientation of 4MeOPEPTC at the D/A interface.

The selective electrochemical determination of rutin in the presence of ascorbic acid (AA) in food at the carbon nanotube (CNT) electrode is presented. The CNT electrode shows ideal characteristics for rutin detection, which are high and distinct response current towards a target, a small base current and high reproducibility/repeatability. In cyclic voltammetry, the prominent current peak that originated from catechol group oxidation in rutin is observed. The performance of the selective determination of rutin at the CNT electrode is in the concentration range of 0.024–4.0 mg ml⁻¹ when the mass ratio of [AA]/[rutin] is up to 2.0.

1,2,4-trimethylbenzene is a halogen-free solvent which dissolves unmodified and modified fullerenes and conjugated polymers. The unique feature enables the study of how the substituent of fullerene affects thermal robustness in bulk heterojunction solar cells using a conjugated polymer PTB7-Th. While 175 °C is the best annealing temperature for a solar cell with unmodified C₇₀, it deteriorates a device with a substituted C₇₀ (C₇₀-PCBM). Additionally, annealing at 175 °C does not change the surface of PTB7-Th:C₇₀ film but makes the surface of PTB7-Th:C₇₀-PCBM film bumpy. The results suggest that the substituent promotes the migration of fullerene in a polymer:fullerene solid composite.

The present study used transparent conductive oxide films as the top electrode of semitransparent organic photovoltaic (ST-OPV) cells. Indium zinc oxide (IZO) was fabricated by a facing direct current magnetron sputtering method for the top electrode of ST-OPV cells with an inverted structure, and then, the effect of selecting a p-type buffer material applicable to IZO films was investigated. Three kinds of p-type buffer materials were examined, namely, molybdenum trioxide (MoO₃), tungsten trioxide-nanoparticles (WO_3-NPs), and dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HATCN). The MoO₃-, WO₃-, and HATCN-based cells yielded power conversion efficiencies (PCEs) of 4.02%, 3.60%, and 3.14%, respectively. After optimization of MoO₃ thickness, the 15 nm thick MoO₃-based cell reached a PCE of 4.84% and a transmittance of 19.9% at a wavelength of 550 nm.

The π-type organic thermoelectric conversion modules composed of p-type and n-type materials that convert low-temperature waste heat into electric energy have the potential to significantly increase energy efficiency. However, p-type and n-type materials are difficult to prepare by similar methods since they have opposite carriers. In this study, we achieved γ-cyclodextrin polymer-carbon nanotube (PγCyD-CNT) composite thermoelectric film that can control the carrier by the solvent effect. When the preparation solvent switched from water to N-methylpyrrolidone (NMP), the carriers of the film were converted from holes to electrons, and their power factor values at 345 K were 221.0 and 246.6 μW m⁻¹K⁻². Moreover, PγCyD-CNTs film prepared in NMP retained n-type characteristics for half a year under the ambient atmosphere. Interestingly, the residual NMP contained in the film acts as a dopant agent for CNTs, and the chemical interaction of γCyD and NMP in the polymer results in sustained n-doping.

Intercellular adhesion strengths of murine breast cancer cells with different malignancies (FP10SC2, highly metastatic and 4T1-LM weakly metastatic) with murine endothelial cells (BMEC) were measured using a cup-attached chip by atomic force microscopy with contact time of the cells between 0 and 60 s. The work required to separate FP10SC2 from a BMEC was larger than that to separate 4T1-LM after short contact times. In addition, cells were greatly elongated at the separation between FP10SC2 and BMEC. From these results, we suggested a model that the adhesion properties of cancer cells measured in this study were representations of detached cancer cells as circulating tumor cells, and highly metastatic cancer cells strongly adhered to endothelial cells with large deformation in floating conditions. These results indicated that our method is useful to study the processes of cancer cell metastasis with respect to intercellular adhesion.

The 3D computer simulation based on the finite element method was performed to obtain the impedance in the presence/absence of adherent living cells. The sensitivity of the inter-digitated electrode was investigated by varying the width (W) and spacing (S) for different number of electrode fingers N. It was found that the peak sensitivity corresponding to W/S < 1 and W/S > 1 exhibited higher sensitivity than W/S = 1. However, the sensitivity was relatively large when W/S < 1. Furthermore, the slope of the peak sensitivity curve decreased with the increase in N, emphasizing the fact that it has greater impact on sensitivity than W/S. It is important to note that the peak sensitivity due to smaller electrode width results in higher sensitivity. Hence, the experimentalists are recommended to choose the smaller electrode geometry with smaller electrode width in order to realize better sensitivity in the presence of adherent cell.

Resilience to stretch stress is an important characteristic that helps maintain cell adhesion and consequently, human health. This study aimed to elucidate the underlying mechanism of adaptation to stretch stress regulated by the molecular chaperone αB-crystallin. Three rat myoblast L6 cell lines, wild type (L6-WT), αB-crystallin knock down (L6-KD), and αB-crystallin overexpressing (L6-OE) cells were used. Muscle cells are less motile because they are specialized for contraction. Forced stretch stress was given to the three cell lines on a soft adhesive sheet, and we found that L6-OE cells showed the highest resilience to stretch stress and the least motility compared to other cell lines. Conversely, L6-KD cells showed the least resilience to stretch stress. Vinculin staining showed that total focal adhesion (FA) size and area of L6-OE cells were significantly larger than those of other cell types. Thus αB-crystallin in myoblast cells contributes the resilience of FA stability during stretch stress.

Perpendicularly oriented vinylidene fluoride oligomer thin films with six molecular layers were poled during vacuum evaporation (in situ poling) using a micro-gapped comb-like electrode, and their pyroelectric characteristics were investigated. The extent of polarization achieved with in situ poling performed by applying a low electric field (7.7 MV m⁻¹) is the same as that achieved by conventional post-poling with the application of a high electric field (>100 MV m⁻¹). Despite using a film with a few molecular layers, the in situ poled sensor showed pyroelectric response without the use of an infrared ray absorption layer; voltage sensitivity of 198 V W⁻¹ was obtained, which is much higher than that of the post-poled sensor (∼16 V W⁻¹). The improvement in sensitivity is attributed to the amount of charge injected during the poling treatment.

Flexible piezoelectric devices with poly (vinylidene fluoride–trifluoroethylene) thin films were fabricated, and directly monitoring of the heart state and piezoelectric power generation were investigated using the pulsating 3D heart model. By attaching the flexible piezoelectric devices to the 3D heart model, the piezoelectric responses corresponding to the pulsation of the right and left ventricles were observed and reflected the status of heart. The maximum output voltage was obtained in the front of the right ventricle of the heart model. The output energy, which caused from piezoelectric effect, improved linearly with the increase of the device area, and was estimated to be approximately 8 nJ mm⁻² per heartbeat.

Size effect of metal nanodome arrays on performance characteristics of a plasmonic biosensor is investigated using reflection spectroscopy. Ag and Au nanodome arrays are created by a bottom-up nanofabrication process by which the dome diameter and metal thickness can be controlled. Reflectivity measurements of metal nanodome arrays showed that the wavelengths and width of resonance dip were changed by the dome diameter and metal thickness, respectively. Bulk refractive index (RI) sensing and detection of DNA hybridization were performed to characterize the sensing performance of metal nanodome arrays. Bulk RI sensitivity were significantly improved as the dome diameter enlarged from 100 to 500 nm. In contrast, metal nanodome arrays with smaller diameter exhibited higher sensor signals against the immobilization of DNA modified gold nanoparticles used for signal amplification indicating strong plamonic coupling effects. With respect to the dome diameter, the effect of metal thickness was moderate for the presented sensing scheme.

The MgZnO/SiO₂/ZnO metal–semiconductor–metal (MSM) dual-band UVA and UVB photodetectors (PDs) with different MgZnO thicknesses were fabricated by RF sputter. From the dark current, it was found that the PD with 200 nm thick MgZnO had a lower leakage current, which implies less defect density and better crystal quality. Therefore, the FWHM of the X-ray diffraction and grain size of the scanning electron microscope image for PDs with a thicker MgZnO thickness were narrower and larger than those of the others. From the photoluminescence (PL) at room temperature, the main defect types of the MgZnO/SiO₂/ZnO thin film included O_v, O_i, and Zn_i. Then, a variable and voltage-controlled tunable wavelength of UV PD from UVB to UVA can be well accomplished by using a SiO₂ blocking layer inserted between the MgZnO and ZnO thin film. Therefore, at a lower and higher bias voltage, the PD with a 200 nm thick MgZnO can detect the UVB and UVA range, respectively.

We developed a novel detection method for the pesticide dichlorvos (2,2-dichlorovinyl dimethyl phosphate) in which tris[4,4,5,5,6,6,6-heptafluoro-1-(2-naphthyl)-1,3-hexanedionato]europium(III) [Eu(III)(hfnh)₃] served as a highly sensitive luminescent probe. The photoluminescence intensity of Eu(III)(hfnh)₃ was drastically and rapidly decreased by the action of dichlorvos in ethyl acetate. The quantum yield of Eu(III)(hfnh)₃ decreased monotonically with increasing dichlorvos concentration, explaining the decrease in photoluminescence intensity. Dynamic and static quenching mechanisms possibly co-existed in ethyl acetate because the Stern–Volmer plot of Eu(III)(hfnh)₃ and dichlorvos could be approximated by a quadratic function. ³¹P-NMR revealed that dichlorvos molecules coordinated to Eu(III) and exhibited dynamic behavior supporting a dynamic quenching mechanism. When dichlorvos was mixed with Eu(III)(hfnh)₃1, Φ_ET drastically decreased from 0.64 to 0.15. A plausible mechanism is that quenching of Eu(III)(hfnh)₃1 occurred between the dichlorvos molecules and the β-diketonates before energy transfer from the β-diketonates to Eu(III). Density functional theory calculations support this mechanism.

A poly[(methyl methacrylate/2,2,2-trifluoroethyl methacrylate/benzyl methacrylate) = 52/42/6 (w/w/w)] copolymer was used to form the core of a polymer optical fiber (POF) with the purpose of fabricating a birefringence-reduced core (BRC). The fabricated POF showed almost no phase shift, regardless of the stress that was applied to the fiber. Therefore, it is possible to maintain the polarization in the POF core, which is an important factor for detection of the direction in which stress is applied to the POF. To detect the stress direction, the core of a BRC–POF was doped with dichroic dye. A doped BRC–POF that was fabricated using magenta dye showed variations in its output under operating conditions where the stress vector and the incident polarization formed different angular relationships. The results presented here are considered to be applicable to detailed structural monitoring using POFs.

A fiber-optic strain sensor using a fluorophore-doped polymer optical fiber (POF) was fabricated at various waveguiding conditions. The effects attributed to each structural feature of the sensor were characterized by observing the sensor's response. Two fluorophores, Coumarin 540A and Rhodamine 6G, were used to dope the core and the cladding of a poly(methyl methacrylate)-based POF, respectively. Using doped POFs with different numerical apertures (NAs), the changes in the fluorophore peaks upon the application of stress were analyzed by applying macrobending(s) to the fiber. Although the sensor response did not show linearity with respect to the NA, it was found that the shape of the Coumarin 540A-attributed peak was a factor that represented the sensor's sensitivity. As a result, the double-cladding structure demonstrated its effectiveness in improving the stress sensitivity.

Different types of platelet-shaped graphene were used as structural and conductive filler of the carbon nanotube (CNT) porous electrode films of a dry-type polymer actuator consisting of CNT, ionic liquid, and a base polymer to enhance actuation performance. The strain and blocking force were evaluated from the bending motion of the actuator with a frequency response from 10 to 0.005 Hz. Ten types of CNT electrode film were prepared by varying the surface areas and added amounts of the graphene. When the same amount of platelet-shaped graphene (50 mg) as that of CNT (50 mg) was added to the CNT electrode, the generated force became almost twice that of CNT (50 mg) without any graphene additives, while the observed displacement remained a similar value. The addition of platelet-shaped graphene improves the expansion and generated stress of the three-layer actuator consisting of CNT electrodes.

Active oxygen species (AOS) generated in the atmosphere can be applied in various industrial processes owing to their extremely strong oxidative ability. Methylene blue (MB) decolors upon exposure to AOS owing to dye degradation; this property can be used to detect the AOS. To detect AOS with higher oxidative ability, it is necessary to stabilize MB by mixing it with sodium alginate. In our previous work, we showed that the OH^* concentration in the AOS increased under the high-humidity condition. Herein, the decolorization mechanism of MB-dyed sodium alginate thin films upon exposure to AOS was elucidated under low- and high-humidity conditions; decolorization was observed only under the latter. We analyzed an MB-dyed sodium alginate thin film indicator to elucidate the chemical reactions occurring as well as the decolorization mechanism generated under the high-humidity condition. We found that the decolorization of the film was caused by MB decomposition upon exposure to the AOS generated under the high-humidity condition.