We developed a machine learning model that predicts with 91.0% accuracy whether a pi-conjugated organic semiconductor adopts a herringbone packing motif, a key motif associated with high carrier mobility. In addition, model interpretation identifies the molecular fragments that promote or suppress herringbone packing, providing practical design guidelines for developing high-performance organic semiconductors.

Solution-based chemical doping provides a simple and effective approach to controlling the carrier concentration of organic semiconductors through redox reactions. However, the role of molecular oxygen, which is the most abundant oxidant in air, has remained unclear. In this study, we demonstrate efficient oxygen-driven doping in aqueous solution by employing highly hydrophobic anions. Specifically, the use of tetrakis(pentafluorophenyl)borate (TFPB-) as the dopant anion significantly enhances the doping efficiency and results in high electrical conductivity of up to 200 S cm-1. This enhancement is attributed to increased anion activity at the solid-liquid interface. Quartz crystal microbalance measurements reveal that hydrophobic anions spontaneously aggregate in the aqueous phase and rapidly adsorb onto the organic semiconductor surface within 15 seconds. This work presents a simple and efficient strategy for oxygen-mediated doping. It also introduces a new design principle for controlling doping processes through interfacial molecular interactions.

The increasing use of disposable sensor devices has raised concerns regarding environmental contamination and resource sustainability. However, design principles for disposable sensor systems under explicit material constraints have not been sufficiently explored. In this work, we propose a material-oriented design framework for disposable sensor systems based on hazard potential and elemental abundance. Guided by this framework, we develop an organic complementary transistor with carbon-based electrodes and a magnesium–air battery designed to avoid selected regulated hazardous substances and elements with low crustal abundance under the proposed criteria. As a proof of concept, we implement a disposable moisture-responsive sensor node integrating the developed transistor and battery. The implemented node generated a supply voltage of 14.8–15.6 V after moisture activation and transmitted a 3-bit ID at 6.7 bit/s using a 140-Hz carrier. We further fabricate and experimentally verify a single-chip integrated sensor circuit, confirming the essential circuit functions required for the proposed sensor node. These results demonstrate a material-constrained design methodology for disposable event-detection sensor nodes, in which the power source, sensing activation mechanism, and organic circuit are co-designed to reduce material-related concerns.

Molecular packing is crucial for charge-transport properties of organic semiconductors (OSCs). Nowadays, most OSCs consist of the π-electron core and insulating side-chain substituents. While the former is the primary factor of molecular packing and resultant charge transport, the latter is also the significant tuning element for them. Hence, it is worth addressing their individual roles. In this work, a potential impact of fluorine substitution on molecular packing and charge-transport properties is reported based on the positional isomers of n-type OSCs which have phenethyl side chains: para-, meta- and ortho-substituted derivatives called p-FPhC2-BQQDI, m-FPhC2-BQQDI and o-FPhC2-BQQDI, respectively. Crystallographic analyses showed that the fluorine substitution position varies the intermolecular interactions through noncovalent C-H∙∙∙F interactions. Although resultant brickwork-type molecular packings suggested similar charge-transport capabilities, single-crystal thin-film transistor assessments revealed distinct differences in the electron mobility: 0.44, 0.92 and 3.56 cm2 V-1 s-1 for o-FPhC2-BQQDI, m-FPhC2-BQQDI and p-FPhC2-BQQDI, respectively. The difference between m-FPhC2-BQQDI and p-FPhC2-BQQDI is attributed to dynamic disorder effects based on molecular dynamics simulations, whereas the lowest mobility of o-FPhC2-BQQDI may further result from static, orientational disordering of the side chains revealed by X-ray crystallography. These findings will be useful for in-depth investigations of side-chain effects on charge-transport properties of OSCs.

Organic electrochemical transistors (OECTs) are emerging as promising platforms for low-voltage bioelectronics applications. However, the use of sharp switching behavior for sensing has remained a challenge due to effects of structural disorders and operational stability. In this study, we report OECTs with subthreshold swings close to or even below the thermodynamic limit of 60 mV dec−1. The sharp switching owe to the semicrystalline nature of the employed thin films showing reversible dopant ion intercalation responding to the gate bias. Furthermore, the introduction of a Langmuir-Blodgett amphiphilic membrane at the semiconductor-electrolyte interface effectively suppressed performance drift. The drift in threshold voltage was as small as 0.18 mV per hour, enabling the use of subthreshold regions for sensing applications. By leveraging the pH-responsivity of the functional monolayer, pH sensing was demonstrated. This work demonstrates benchmark switching performance and stability of OECTs, and the potential of supramolecular interface engineering for sensing platforms.

Accurate pH monitoring in flexible thin films is essential for biochemical sensing applications. However, in conventional soft-material-based film-type pH sensors, the apparent pH response is often influenced by variations in thin-film morphology, such as swelling, microstructural disorder, and structural inhomogeneity. Here, we adopt a different strategy by confining a small-molecule proton-coupled electron-transfer (PCET) redox couple, traditionally used in homogeneous aqueous solutions, within an ion gel. A benzoquinone/hydroquinone (BQ/HQ) redox couple is incorporated into an ion-gel matrix deposited on a gold electrode and covered with a Nafion overlayer. The open-circuit potential of the Au/ion-gel interface, measured against an Ag/AgCl reference electrode, exhibits a Nernstian dependence on pH, indicating that the proton-coupled BQ/HQ redox equilibrium is preserved in the thin-film device. These results demonstrate that PCET redox couples homogeneously dissolved in ion gels provide a viable route toward compact and reliable pH-sensing films.

Doping is a cornerstone of semiconductor engineering, yet conventional methods lack precise and uniform control over electronic properties. Here, we present a highly controllable voltage-programmed electrochemical doping strategy utilizing pulsed gate voltage sequences to orchestrate anion/cation ingress into polymer matrices. This approach, applied to the benchmark semicrystalline p-type polymer poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) and the cyano-functionalized bithiophene imide dimer (CNI2)-based n-type polymer, overcomes the limitations of chemical doping by delivering exceptional scalability and tunability, achieving conductivities of up to 685 and 21 S cm- 1, respectively. These gains arise from optimized electronic properties and enhanced polymer crystallinity enabled by precise voltage-driven ion intercalation. Notably, this enables a Hall mobility of 2.6 cm2 V- 1 s- 1 at 300 K and signatures of mesoscopic phase-coherent transport, as evidenced by the observation of Hall effect signals and positive magnetoresistance associated with weak localization. This study establishes a generalizable framework for engineering charge transport in conjugated polymers for advanced electronic and spintronic applications.

Molecular doping has enabled control of electronic properties in semiconducting polymers for studies of charge transport and device applications. However, conventional dopant anions are mostly organic monovalent species whose roles are largely limited to stable charge compensation. Here, we introduce polyoxometalates as multivalent oxide-cluster dopant ions into semicrystalline polymer semiconductors. In particular, films doped with size-compatible divalent [W _6 O _19 ] $ ^{2-}$ retain lamellar order, exhibit conductivity above 200 S cm $ ^{-1}$ , and show a Hall response, indicating partially coherent carrier transport. Compared with inert-anion-doped films, [W _6 O _19 ] $ ^{2-}$ -doped films show enhanced anodic response in the oxygen-evolution region, demonstrating functional multivalent-ion doping for electronic and electrocatalytic polymer semiconductor films.

Orientational control of polymeric semiconductors (PSs) is a fundamental technology for understanding and improving the carrier transport properties. Although PS thin films have been fabricated through facile solution processes, complex convection flows during solvent evaporation often limit the scalability and reproducibility of orientational control. To address these problems, we developed a circular flow alignment method for PS thin films. PS solutions were dropped on glycerol flowing in a circular motion inside a container to obtain thin films at the air-liquid interface. The resulting thin films showed alignment of the main chains along the flow direction, which suppressed the effects of convection flows during solvent evaporation. Anisotropic characteristics were observed in the thin-film structure as evaluated by X-ray diffraction measurements, optical absorption, and carrier transport properties, which serve as supporting evidence for the uniaxial alignment of the PS main chains. In field-effect transistors, a mobility of 0.13 cm2  V-1  s-1 was observed under atmospheric conditions, which was four times higher than that of spin-coated thin films. Considering that macroscopic liquid flows are easily controlled, the proposed flow alignment method may serve as a scalable and facile method for fabricating highly aligned PS thin films for various applications.

Exciton dissociation into free electron-hole carriers is a central issue in optoelectronic devices. Despite recent progress in free-carrier generation due to an admixture of organic compounds, strategies to prolong the lifetime of photo-induced carriers are limited. Herein, we present a proof-of-concept of efficient exciton dissociation via heterogeneous device engineering; an insulating polymer layer adjacent to organic semiconductors (OSCs) in conjunction with an application of electrical voltage can capture photogenerated electrons selectively, and the resulting semipermanent built-in electric field gives rise to extraordinarily persistent photo-induced carriers, which lasts for more than half a year in single-crystalline OSCs.

A highly periodic electrostatic potential and coherent band transport can emerge in organic molecular crystals, despite weak van der Waals interactions. Although charge carrier mobility in single-crystalline organic semiconductors (OSCs) reaches 10 square centimeters per volt per second (cm2 V-1 s-1), it is predominantly limited by molecular vibrations excited at room temperature. The extent to which mobility in single-crystalline OSCs can be increased remains a central question. Here, we demonstrate charge transport in a clean two-dimensional hole gas (2DHG) in uniaxially strained, single-crystalline OSCs at cryogenic temperatures, with minimized lattice vibrations. Hall effect measurements reveal a mobility of 117 cm2 V-1 s-1 at 2 kelvin under 2.8% compressional strain, with an extraordinarily large piezoresistive effect and low sheet resistivity of 550 ohms, one-fifth of the lowest resistivity in unstrained samples. These clean systems offer opportunities to explore intrinsic strain-induced charge transport physics, where condensed matter phenomena, characterized by weakly bonded molecular orbitals, combine electronic correlation and lattice degrees of freedom.

Single-crystal organic semiconductors (OSCs) hold immense potential for high-performance thin-film transistors (TFTs) due to their high charge-carrier mobilities (µ) stemming from defect-free and long-range-order structure. While µ is a key factor of TFT performance and can be tackled by molecular design of OSCs, threshold voltage (Vth) significantly impacts operational voltage and power consumption in integrated circuits and is typically controlled by device engineering. A traditional Vth tuning method involves interfacial modifications of gate-dielectric surface by self-assembled monolayers (SAMs) with different dipolar characters. Yet, the SAM is less compatible with printed electronics using polymeric gate dielectrics. Therefore, controlling Vth through OSC material design is of interest. This work demonstrates that Vth in sin-gle-crystal OSCs can be effectively modulated by engineering the dipolar character of side-chain substituents which are widely employed in solution-processable OSCs. To validate this concept, we focused on 3,4,9,10-benzo[de]isoquinolino[1,8-gh]quinolinetetracarboxylic diimide (BQQDI) derivatives because they have formed compara-ble layered brickwork packing structures mostly irrespective of the side-chain structures. Stemming from the bench-marked, phenethyl-substituted BQQDI (PhC2−BQQDI), here, three PhC2−BQQDI analogues with mono-fluorination at the ortho, meta or para position of the phenyl ring were synthesized. These compounds were designed to maintain isostruc-tural crystal packing while varying the dipolar character of the side chains. In solution-processed single-crystal TFTs, obvious Vth shifts depending on the fluorine substitution position were found. By crystal structure and computational analyses, the Vth shift was correlated with the dipolar character of the side chains at the OSC−gate dielectric interface. This side-chain-engineered dipolar effect is not only useful for Vth control in TFTs but also proposes new avenues for de-signing high-performance OSCs and various thin-film devices with tailored interfacial properties.

Thin-film single crystals of organic semiconductors represent a emerging class of materials for flexible printed electronic devices, including organic field-effect transistors and strain sensors. Their potential arises from the demonstration of high-mobility band transport, which significantly enhances both device performance and operational reliability. However, achieving stable and precise control over carrier concentration through chemical doping remains a fundamental challenge, restricting device architecture and broader application. In this study, the challenge is addressed by improving the environmental and thermal stability of chemically doped organic single crystals through the strategic selection of dopant anions. Specifically, ion-exchange doping using the bulky tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (BArF) anion resulted in high electrical conductivity and exceptional stability under ambient conditions at 80 degrees C. The doped single crystals further exhibited excellent strain sensitivity, maintaining consistent strain sensing performance over 100 000 bending cycles, with conductivity drift suppressed to the order of ppm per hour under ambient conditions. These results highlight the importance of dopant ion design for stabilizing the doped state of organic semiconductors under environmental stress, without compromising mechanical flexibility or electronic functionality. This approach paves the way for robust and reliable flexible organic electronic devices.

Solution processing of organic semiconductors provides a facile way to fabricate electrically doped thin films, which opens opportunities for advancing printed electronics. However, this approach is limited due to the instability of dopants and doped organic semiconductors, particularly for n-type ones. In this study, n-type doping of an organic semiconducting polymer is achieved using aqueous doping solutions in air, a condition under which n-type chemical doping had not previously been demonstrated. Polymeric semiconductor thin films are immersed in aqueous doping solutions, which contained the saccharide fructose, redox bio-mediator flavin nucleotide (FMN), and bulky molecular cations. In this process, electrons are transferred from fructose to FMN and then from FMN to organic semiconductor thin films. The introduced electrons are compensated by the incorporation of bulky molecular cations into the thin films. Successful n-type doping is confirmed by absorption, conductivity, and photoelectron spectroscopy measurements. The density of states of the polymer is filled up to -3.8 eV versus vacuum, beyond the conventionally anticipated limit of ambient stability. This breakthrough is rooted in the combined effects of solution pH, mediator-assisted use of fructose, and choice of dopant cation. In addition, n-type doping using biomolecules may shed light on new connections between electronic materials and biomolecules for energy storage, transfer, and conversion.

Solution processing of polymeric semiconductors provides a facile way to fabricate functional diodes. However, energy barriers at metal-semiconductor interfaces often limit their performance. Here, we report rectifying polymer diodes with markedly modified energy-level alignments. The gold electrode surface was treated with a dimeric metal complex, which resulted in a shallow work function of 3.7 eV by forming a monolayer-thick ionized donor layer. When a polymeric semiconductor was coated on the treated electrode, most of the ionized donors remained at the metal-semiconductor interface. The confined ionized donors with the ideal thickness enabled fabrication of a polymer diode with a forward current density of over 100 A cm-2. Furthermore, a power conversion efficiency of 7.9% was observed for rectification at a microwave frequency of 920 MHz, which is orders of magnitude higher than that reported for organic diodes. Our findings will pave a way to solution-processed high-frequency and high-power devices.

We present a scalable flexible active-matrix mini-LED display, which consists of bezelless 3-mm pitch 30 cm x 30 cm independently operating modules. The backplane is based on high-performance organic single-crystal TFTs laminated on screen-printed large-area plastic substrates. The organic TFTs are separately formed on a polyimide film using photolithography. Since their speed and on-current is crucial on flexible films to operate LED chips with sufficient brightness, we employ high-performance organic single-crystal transistors. The value of the mobility exceeds 10 cm2/Vs. The matrix wirings of silver paint are printed by a large-area screen printing method, so that the vertical and horizontal lines are electrically separated by an insulating layer.

Doped interlayers were employed to improve charge injection from copper electrodes into high-mobility organic single-crystal semiconductors, addressing both economic and material sustainability challenges in organic electronics.

Strong electron correlation is the essential mediator that creates various exotic phases in two-dimensional electronic systems which has been continuously intriguing in modern condensed-matter physics. Such electronic states as Mott insulators, charge orders, and high-temperature superconductivity would be simply Fermi-degenerated metals unless the strong correlation plays essential roles. However, how it emerges, particularly to overcome screening effects upon doping band insulators, has not been experimentally studied. In this study, we report evolution of a strongly correlated electron system from a band-insulating organic semiconductor. Carriers are continuously doped via electric double layers up to a density of 1014 cm-2. Notably, significant deviations from a simple metallic system are observed even at far from half-filled band, possibly due to charge-order instability. The findings reveal that off-site Coulomb energy can compete with Thomas-Fermi screening. This competition enables the emergence of strongly correlated exotic phases, even in systems distant from Mott insulators.

Transistors fabricated from thin‐film single crystals of organic semiconductors (OSCs) have exhibited high mobility exceeding 10 cm 2 V −1 s −1 and show compatibility with low‐cost solution processing. However, their carrier mobility is limited by the molecular vibrations in their soft lattices. This study establishes a practical method for applying compressive strain to single‐crystal OSCs to enhance mobility and transistor performance. In this method, a polymer film substrate is bent to mechanically stretch its surface. Organic single‐crystal transistors are then laminated onto the stretched surface of substrate. Releazing the stretch by recovering the flat surface of the substrate allowed the transistors to be compressed by up to 3%. This resulted in a 52% increase in mobility, reaching 26.4 cm 2 V −1 s −1 . X‐ray diffraction measurements confirmed lattice strain in the OSC single crystals. Moreover, carrier mobility and cutoff frequency increased in MHz‐operating short‐channel transistors, demonstrating applicability for high‐frequency devices. The mobility increase is maintained even three years after introducing the 1% compressive strain, possibly owing to the flexible, molecularly thin characteristics of OSC single crystals. The proposed strain management methods may provide new avenues to enhance the performance of high‐mobility and high‐frequency electronic devices based on OSC thin‐film single crystals.