Critical assessment of charge mobility extraction in FETs

Crucial role of interfacial thermal dissipation in the operational stability of organic field-effect transistors

The operational stability becomes a key issue affecting the commercialization for organic field-effect transistors (OFETs). It is widely recognized to be closely related to the defects and traps at the interface between dielectric and organic semiconductors, but this understanding does not always effectively address operational instability, implying that the factors influencing the operational stability have not been fully understood. Here, we reveal that the self-heating effect is another crucial factor in operational stability. By using hexagonal boron nitride (hBN) to assist interfacial thermal dissipation, the dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) FETs exhibit high mobility of 14.18 cm2 V-1 s-1 and saturated power density up to 1.8 × 104 W cm-2. The OFET can operate at a power density of 1.06 × 104 W cm-2 for 30,000 s with negligible performance degradation, showing excellent operational stability under high power density. This work deepens the understanding on operational stability and develops an effective way for ultrahigh stable devices.

Downscaling of Organic Field-Effect Transistors based on High-Mobility Semiconducting Blends for High-Frequency Operation

Small molecule/polymer semiconductor blends are promising solutions for the development of high-performing organic electronics. They are able to combine ease in solution processability, thanks to the tunable rheological properties of polymeric inks, with outstanding charge transport properties thanks to high crystalline phases of small molecules. However, because of charge injection issues, so far such good performances are only demonstrated in ad-hoc device architectures, not suited for high-frequency applications, where transistor dimensions require downscaling. Here, the successful integration of the most performing blend reported to date, based on 2,7-dioctyl[1] benzothieno[3,2-b][1]benzothiophene (C8-BTBT) and poly(indacenodithiophene-co-benzothiadiazole) (C16IDT-BT), in OFETs characterized by channel and overlap lengths equal to 1.3 and 1.9 µm, respectively, is demonstrated, enabling a transition frequency of 23 MHz at -8 V. Two key aspects allowed such result: molecular doping, leading to width-normalized contact resistance of only 260 Ωcm, allowing to retain an apparent field-effect mobility as high as 3 cm2/(Vs) in short channel devices, and the implementation of a high capacitance dielectric stack, enabling the reduction of operating voltages below 10 V and the overcoming of self-heating issues. These results represent a fundamental step for the future development of low-cost and high-speed printed electronics for IoT applications.

Recent Progress of Fluorinated Conjugated Polymers

In recent years, conjugated polymers have received widespread attention due to their characteristic advantages of light weight, favorable solution processability, and structural modifiability. Among various conjugated polymers, fluorinated ones have developed rapidly to achieve high-performance n-type or ambipolar polymeric semiconductors. The uniqueness of fluorinated conjugated polymers contains the high coplanarity of their structures, lower frontier molecular orbital energy levels, and strong nonbonding interactions. In this review, first the fluorinated building blocks, including fluorinated benzene and thiophene rings, fluorinated B←N bridged units, and fluoroalkyl side chains are summarized. Subsequently, different synthetic methods of fluorinated conjugated polymers are described, with a special focus on their respective advantages and disadvantages. Then, with these numerous fluorinated structures and appropriate synthetic methods bear in mind, the properties and applications of the fluorinated conjugated polymers, such as cyclopentadithiophene-, amide-, and imide-based polymers, and B←N embedded polymers, are systematically discussed. The introduction of fluorine atoms can further enhance the electron-deficiency of the backbone, influencing the charge carrier transport performance. The promising fluorinated conjugated polymers are applied widely in organic field-effect transistors, organic solar cells, organic thermoelectric devices, and other organic opto-electric devices. Finally, the outlook on the challenges and future development of fluorinated conjugated polymers is systematically discussed.

Covalent Bond Torsion-Enabled Unique Crystal-Phase Transformation of an Organic Semiconductor for Multicolor Light-Emitting Transistors

High-mobility and color-tunable highly emissive organic semiconductors (OSCs) are highly promising for various optoelectronic device applications and novel structure-property relationship investigations. However, such OSCs have never been reported because of the great trade-off between mobility, emission color, and emission efficiency. Here, we report a novel strategy of molecular conformation-induced unique crystalline polymorphism to realize the high mobility and color-tunable high emission in a novel OSC, 2,7-di(anthracen-2-yl) naphthalene (2,7-DAN). Interestingly, 2,7-DAN has unique crystalline polymorphism, which has an almost identical packing motif but slightly different molecular conformation enabled by the small bond rotation angle variation between anthracene and naphthalene units. More remarkably, the subtle covalent bond rotation angle change leads to a big change in color emission (from blue to green) but does not significantly modify the mobility and emission efficiency. The carrier mobility of 2,7-DAN crystals can reach up to a reliable 17 cm2 V-1 s-1, which is rare for the reported high-mobility OSCs. Based on the unique phenomenon, high-performance light-emitting transistors with blue to green emission are simultaneously demonstrated in an OSC crystal. These results open a new way for designing emerging multifunctional organic semiconductors toward next-generation advanced molecular (atomic)-scale optoelectronics devices.

Non-covalent planarizing interactions yield highly ordered and thermotropic liquid crystalline conjugated polymers

Controlling the multi-level assembly and morphological properties of conjugated polymers through structural manipulation has contributed significantly to the advancement of organic electronics. In this work, a redox active conjugated polymer, TPT-TT, composed of alternating 1,4-(2-thienyl)-2,5-dialkoxyphenylene (TPT) and thienothiophene (TT) units is reported with non-covalent intramolecular S⋯O and S⋯H-C interactions that induce controlled main-chain planarity and solid-state order. As confirmed by density functional theory (DFT) calculations, these intramolecular interactions influence the main chain conformation, promoting backbone planarization, while still allowing dihedral rotations at higher kinetic energies (higher temperature), and give rise to temperature-dependent aggregation properties. Thermotropic liquid crystalline (LC) behavior is confirmed by cross-polarized optical microscopy (CPOM) and closely correlated with multiple thermal transitions observed by differential scanning calorimetry (DSC). This LC behavior allows us to develop and utilize a thermal annealing treatment that results in thin films with notable long-range order, as shown by grazing-incidence X-ray diffraction (GIXD). Specifically, we identified a first LC phase, ranging from 218 °C to 107 °C, as a nematic phase featuring preferential face-on π-π stacking and edge-on lamellar stacking exhibiting a large extent of disorder and broad orientation distribution. A second LC phase is observed from 107 °C to 48 °C, as a smectic A phase featuring sharp, highly ordered out-of-plane lamellar stacking features and sharp tilted backbone stacking peaks, while the structure of a third LC phase with a transition at 48 °C remains unclear, but resembles that of the solid state at ambient temperature. Furthermore, the significance of thermal annealing is evident in the ∼3-fold enhancement of the electrical conductivity of ferric tosylate-doped annealed films reaching 55 S cm-1. More importantly, thermally annealed TPT-TT films exhibit both a narrow distribution of charge-carrier mobilities (1.4 ± 0.1) × 10-2 cm2 V-1 s-1 along with a remarkable device yield of 100% in an organic field-effect transistor (OFET) configuration. This molecular design approach to obtain highly ordered conjugated polymers in the solid state affords a deeper understanding of how intramolecular interactions and repeat-unit symmetry impact liquid crystallinity, solution aggregation, solution to solid-state transformation, solid-state morphology, and ultimately device applications.

Tracking Cation Exchange in Individual Nanowires via Transistor Characterization

Cation exchange is a versatile method for modifying the material composition and properties of nanostructures. However, control of the degree of exchange and material properties is difficult at the single-particle level. Successive cation exchange from CdSe to Ag2Se has been utilized here on the same individual nanowires to monitor the change of electronic properties in field-effect transistor devices. The transistors were fabricated by direct synthesis of CdSe nanowires on prepatterned substrates followed by optical lithography. The devices were then subjected to cation exchange by submerging them in an exchange solution containing silver nitrate. By removal of the devices from solution and probing the electrical transport properties at different times, the change in electronic properties of individual nanowires could be monitored throughout the entire exchange reaction from CdSe to Ag2Se. Transistor characterization revealed that the electrical conductivity can be tuned by up to 8 orders of magnitude and the charge-carrier mobility by 7 orders of magnitude. While analysis of the material composition by energy dispersive X-ray spectroscopy confirmed successful cation exchange from CdSe to Ag2Se, X-ray fluorescence spectroscopy proved that cation exchange also took place below the contacts. The method presented here demonstrates an efficient way to tune the material composition and access the resulting properties nondestructively at the single-particle level. This approach can be readily applied to many other material systems and can be used to study the electrical properties of nanostructures as a function of material composition or to optimize nanostructure-based devices after fabrication.

Engineered solid-state aggregates in brickwork stacks of n-type organic semiconductors: a way to achieve high electron mobility

Efficient, economically viable n-type organic semiconductor materials suitable for solution-processed OFET devices with high electron mobility and ambient stability are scarce. Merging these attributes into a single molecule remains a significant challenge and a careful molecular design is needed. To address this, synthetic viability (achievable in fewer than three steps) and using cost-effective starting materials are crucial. Our research presents a strategy that meets these criteria using naphthalene diimide (NDI) core structures. The approach involves a simple synthesis process with a cost of $ 5-10 per gram for the final products. This paper highlights our success in scaling up the production using affordable known reagents, creating ambient condition solution-processed OFET devices with impressive electron mobility, on-off current ratio (1 cm2 V-1 s-1 and I on/I off ∼ 109) and good ambient stability (more than 100 h). We conducted a comprehensive study on EHNDIBr2, a material that demonstrates superior performance due to its unique supramolecular arrangement in its brickwork stack. This was compared with two similar structures to validate our findings. The superior performance of EHNDIBr2 is attributed to the effective interlocking of charge-hopping units within the NDI core in its brickwork stack. Our findings include detailed electronic, spectroscopic, and microscopic analyses of these layers.

Electrical Polarity Modulation in V-Doped Monolayer WS2 for Homogeneous CMOS Inverters

As demand for higher integration density and smaller devices grows, silicon-based complementary metal-oxide-semiconductor (CMOS) devices will soon reach their ultimate limits. 2D transition metal dichalcogenides (TMDs) semiconductors, known for excellent electrical performance and stable atomic structure, are seen as promising materials for future integrated circuits. However, controlled and reliable doping of 2D TMDs, a key step for creating homogeneous CMOS logic components, remains a challenge. In this study, a continuous electrical polarity modulation of monolayer WS2 from intrinsic n-type to ambipolar, then to p-type, and ultimately to a quasi-metallic state is achieved simply by introducing controllable amounts of vanadium (V) atoms into the WS2 lattice as p-type dopants during chemical vapor deposition (CVD). The achievement of purely p-type field-effect transistors (FETs) is particularly noteworthy based on the 4.7 at% V-doped monolayer WS2, demonstrating a remarkable on/off current ratio of 105. Expanding on this triumph, the first initial prototype of ultrathin homogeneous CMOS inverters based on monolayer WS2 is being constructed. These outcomes validate the feasibility of constructing homogeneous CMOS devices through the atomic doping process of 2D materials, marking a significant milestone for the future development of integrated circuits.

Low Contact Resistance Organic Single-Crystal Transistors with Band-Like Transport Based on 2,6-Bis-Phenylethynyl-Anthracene

Contact resistance has become one of the main bottlenecks that hinder further improvement of mobility and integration density of organic field-effect transistors (OFETs). Much progress has been made in reducing contact resistance by modifying the electrode/semiconductor interface and decreasing the crystal thickness, however, the development of new organic semiconductor materials with low contact resistance still faces many challenges. Here, 2,6-bis-phenylethynyl-anthracene (BPEA) is found, which is a material that combines high mobility with low contact resistance. Single-crystal BEPA OFETs with a thickness of ≈20 nm demonstrated high mobility of 4.52 cm2 V-1 s-1, contact resistance as low as 335 Ω cm, and band-like charge transport behavior. The calculated compatibility of the EHOMO of BPEA with the work function of the Au electrode, and the decreased |EHOMO-ΦAu| with the increase of external electric field intensity from source to gate both contributed to the efficient charge injection and small contact resistance. More intriguingly, p-type BPEA as a buffer layer can effectively reduce the contact resistance, improve the mobility, and meanwhile inhibit the double-slope electrical behavior of p-channel 2,6-diphenyl anthracene (DPA) single-crystal OFETs.

Optimized Incorporation of Furan into Diketopyrrolopyrrole-Based Conjugated Polymers for Organic Field-Effect Transistors

Flexible electronics have received considerable attention in the past decades due to their promising application in rollable display screens, wearable devices, implantable devices, and other electronic applications. In particular, conjugated polymers are favored for flexible electronics due to their mechanical flexibility and potential for solution-processed fabrication techniques, such as blade-coating, roll-to-roll printing, and high-throughput printing allowing for high-performance transistor devices. Thiophene is the prevailing conjugated unit to construct these conjugated polymers due to its favorable electronic properties. On the other hand, furans are among the few conjugated moieties that are easily derived from bio renewable resources. To promote sustainability, we selectively introduced furan into the conjugated backbone of a high-mobility polymer scaffold and systematically studied the effect on the microstructure and charge transport. We show that partially and selectively replacing thiophene units with furan can yield nearly comparable performance compared to the all-thiophene polymer. This strategy offers an improvement in the sustainability of the polymer by incorporating bio-sourced furan without sacrificing the high-performance characteristics. Meanwhile, polymers with incorrect or complete furan incorporation show reduced mobilities. This work serves to develop coherent structure-morphology-performance relationships; such knowledge will establish guidelines for the future development of sustainable, furan-based conjugated materials.

β-Disubstituted Pentacene Derivatives: Thin Film Structural Properties and Four-Probe Field Effect Mobility

2,9- and 2,10-diphenylpentacene were synthesized by direct C-H borylation of ketal-protected pentacene, followed by halodeboronation, resolution of the dihalo isomers, Suzuki arylation, cleavage of the ketals and decarbonylation in the solid state. They were studied as main active components in organic field effect transistors (OFETs). Diphenyl substitution of pentacene affects the unit cell dimensions only slightly, preserving a face to edge molecular packing in the first layers of thin films evaporated on SiO2 substrates. Both isomers self-assemble into nanoribbons during the thin film growth upon vapor deposition. The similarity between the surface induced phases of the 2,9-isomer and unsubstituted pentacene leads to similar 4-probe hole mobilities, i. e. 0.13 cm2 V-1 s-1 for the former. Whereas 2,9-disubstitution thus does essentially preserve the thin film characteristics of unsubstituted pentacene, 2,10-disubstitution is detrimental to the molecular ordering in the thin films and therefore to the field effect mobility which is only 0.07 cm2 V-1 s-1. The known strong enhancement of field effect mobility observed upon diphenyl substitution of anthracene can thus not be emulated analogously with pentacene.

Seeded growth of single-crystal black phosphorus nanoribbons

Two-dimensional materials have emerged as an important research frontier for overcoming the challenges in nanoelectronics and for exploring new physics. Among them, black phosphorus, with a combination of a tunable bandgap and high mobility, is one of the most promising systems. In particular, black phosphorus nanoribbons show excellent electrostatic gate control, which can mitigate short-channel effects in nanoscale transistors. Controlled synthesis of black phosphorus nanoribbons, however, has remained an outstanding problem. Here we report large-area growth of black phosphorus nanoribbons directly on insulating substrates. We seed the chemical vapour transport growth with black phosphorus nanoparticles and obtain uniform, single-crystal nanoribbons oriented exclusively along the [100] crystal direction. With comprehensive structural calculations, we discover that self-passivation at the zigzag edges holds the key to the preferential one-dimensional growth. Field-effect transistors based on individual nanoribbons exhibit on/off ratios up to ~104, confirming the good semiconducting behaviour of the nanoribbons. These results demonstrate the potential of black phosphorus nanoribbons for nanoelectronic devices and also provide a platform for investigating the exotic physics in black phosphorus.

Achieving Ideal and Environmentally Stable n-Type Charge Transport in Polymer Field-Effect Transistors

Realizing ideal charge transport in field-effect transistors (FETs) of conjugated polymers is crucial for evaluating device performance, such as carrier mobility and practical applications of conjugated polymers. However, the current FETs using conjugated polymers as the active layers generally show certain non-ideal transport characteristics and poor stability. Here, ideal charge transport of n-type polymer FETs is achieved on flexible polyimide substrates by using an organic-inorganic hybrid double-layer dielectric. Deposited conjugated polymer films show highly ordered structures and low disorder, which are supported by grazing-incidence wide-angle X-ray scattering, near-edge X-ray absorption fine structure, and molecular dynamics simulations. Furthermore, the organic-inorganic hybrid double-layer dielectric provides low interfacial defects, leading to excellent charge transport in FETs with high electron mobility (1.49 ± 0.46 cm2 V-1 s-1) and ideal reliability factors (102 ± 7%). Fabricated polymer FETs show a self-encapsulation effect, resulting in high stability of the FET charge transport. The polymer FETs still work with high mobility above 1 cm2 V-1 s-1 after storage in air for more than 300 days. Compared with state-of-the-art conjugated polymer FETs, this work simultaneously achieves ideal charge transport and environmental stability in n-type polymer FETs, facilitating rapid device optimization of high-performance polymer electronics.

A Novel N-Type Molecular Dopant With a Closed-Shell Electronic Structure Applicable to the Vacuum-Deposition Process

Rational design, synthesis, and characterization of a new efficient versatile n-type dopant with a closed-shell electronic structure are described. By employing the tetraphenyl-dipyranylidene (DP0) framework with two 7π-electron systems modified with N,N-dimethylamino groups as the strong electron-donating substituent, 2,2',6,6'-tetrakis[4-(dimethylamino)phenyl]-4,4'-dipyranylidene (DP7), a closed-shell molecule with an extremely high-lying energy level of the highest occupied molecular orbital, close to 4.0 eV below the vacuum level, is successfully developed. Thanks to its thermal stability, DP7 is applicable to vacuum deposition, which allows utilization of DP7 in bulk doping for the development of n-type organic thermoelectric materials and contact doping for reducing contact resistance in n-type organic field-effect transistors. As vacuum-deposition processable n-type dopants are very limited, DP7 stands out as a useful n-type dopant, particularly for the latter purpose.

Enhancing Stability and Performance in Tin-Based Perovskite Field-Effect Transistors Through Hydrogen Bond Suppression of Organic Cation Migration

Ion migration poses a substantial challenge in perovskite transistors, exerting detrimental effects on hysteresis and operational stability. This study focuses on elucidating the influence of ion migration on the performance of tin-based perovskite field-effect transistors (FETs). It is revealed that the high background carrier density in FASnI3 FETs arises not only from the oxidation of Sn2+ but also from the migration of FA+ ions. The formation of hydrogen bonding between FA+ and F- ions efficiently inhibits ion migration, leading to a reduction in background carrier density and an improvement in the operational stability of the transistors. The strategy of hydrogen bond is extended to fluorine-substituted additives to improve device performance. The incorporation of 4-fluorophenethylammonium iodide additives into FETs significantly minimizes the shift of turn-on voltage during cyclic measurements. Notably, an effective mobility of up to 30 cm2 V-1 s-1 with an Ion/off ratio of 107 is achieved. These findings hold promising potential for advancing tin-based perovskite technology in the field of electronics.

Electronic Transport and Quantum Phenomena in Nanowires

Nanowires are natural one-dimensional channels and offer new opportunities for advanced electronic quantum transport experiments. We review recent progress on the synthesis of nanowires and methods for the fabrication of hybrid semiconductor/superconductor systems. We discuss methods to characterize their electronic properties in the context of possible future applications such as topological and spin qubits. We focus on group III-V (InAs and InSb) and group IV (Ge/Si) semiconductors, since these are the most developed, and give an outlook on other potential materials.

The Influence of a Microstructural Conformation of Oriented Floating Films of Semiconducting Polymers on Organic Device Performance

Extended π-conjugation with backbone-planarity-driven π-π stacking dominates charge transport in semiconducting polymers (SCPs). The roles of SCP film morphology and macromolecular conformation concerning the substrate in influencing charge transport and its impact on device performance have been a subject of extensive debate. Face-on SCPs promote out-of-plane charge transport primarily through π-π stacking, with conjugated polymeric chains assisting transport in connecting crystalline domains, whereas edge-on SCPs promote in-plane charge transport primarily through conjugation and π-π stacking. In this work, we fabricated three different types of devices, namely, organic field effect transistors, organic Schottky diodes, and organic bistable memristors, as representatives of planar and vertical devices. We demonstrate that a planar device, i.e., an organic field effect transistor, performs well in an edge-on conformation exhibiting a field-effect mobility of 0.12 cm2V-1s-1 and on/off ratio >104, whereas vertical devices, i.e., organic Schottky diodes and organic memristors, perform well in a face-on conformation, exhibiting exceptionally high on/off ratios of ~107 and 106, respectively.

Tailoring the Morphology of a Diketopyrrolopyrrole-based Polymer as Films or Wires for High-Performance OFETs using Solution Shearing

Conjugated polymers often show efficient charge carrier transport along their backbone which is a primary factor in the electrical behavior of Organic Field Effect Transistor (OFETs) devices fabricated from these materials. Herein, a solution shearing procedure is reported to fabricate micro/nano wires from a diketopyrrolopyrrole (DPP)-based polymer. Millimeter to nanometer long polymer wires orientated in the coating direction are developed after a thorough analysis of the deposition conditions. It shows several morphological regimes-film, transition, and wires and experimentally derive a phase diagram for the parameters coating speed and surface energy of the substrate. The as-fabricated wires are isolated, which is confirmed by optical, atomic force, and scanning electron microscopy. Beside the macroscopic alignment of wires, cross-polarized optical microscopy images show strong birefringence suggesting a high degree of molecular orientation. This is further substantiated by polarized UV-Vis-NIR spectroscopy, selected area electron diffraction transmission electron microscopy, and grazing-incidence wide-angle X-ray scattering. Finally, an enhanced electrical performance of single wire OFETs is observed with a 15-fold increase in effective charge carrier mobility to 1.57 cm2 V-1 s-1 over devices using films (0.1 cm2 V-1 s-1 ) with similar values for on/off current ratio and threshold voltage.

A skeletal randomization strategy for high-performance quinoidal-aromatic polymers

Enhancing the solution-processability of conjugated polymers (CPs) without diminishing their thin-film crystallinity is crucial for optimizing charge transport in organic field-effect transistors (OFETs). However, this presents a classic "Goldilocks zone" dilemma, as conventional solubility-tuning methods for CPs typically yield an inverse correlation between solubility and crystallinity. To address this fundamental issue, a straightforward skeletal randomization strategy is implemented to construct a quinoid-donor conjugated polymer, PA4T-Ra, that contains para-azaquinodimethane (p-AQM) and oligothiophenes as repeat units. A systematic study is conducted to contrast its properties against polymer homologues constructed following conventional solubility-tuning strategies. An unusually concurrent improvement of solubility and crystallinity is realized in the random polymer PA4T-Ra, which shows moderate polymer chain aggregation, the highest crystallinity and the least lattice disorder. Consequently, PA4T-Ra-based OFETs, fabricated under ambient air conditions, deliver an excellent hole mobility of 3.11 cm2 V-1 s-1, which is about 30 times higher than that of the other homologues and ranks among the highest for quinoidal CPs. These findings debunk the prevalent assumption that a random polymer backbone sequence results in decreased crystallinity. The considerable advantages of the skeletal randomization strategy illuminate new possibilities for the control of polymer aggregation and future design of high-performance CPs, potentially accelerating the development and commercialization of organic electronics.

Thienoisoindigo-Based Conjugated Polymers Synthesized by Direct Arylation Polycondensation

A series of thienoisoindigo (TIG)-based conjugated polymers (CPs) with high molecular weights are synthesized by direct arylation polycondensation (DArP) by using TIG derivatives as CBr monomer and multi-halogenated thiophene derivatives, i.e., (E)-1,2-bis(3,4-difluorothien-2-yl)ethene (4FTVT), (E)-1,2-bis(3,4-dichlorothien-2-yl)ethene (4ClTVT), 3,3',4,4'-tetrafluoro-2,2'-bithiophene (4FBT), and 3,3',4,4'-tetrachloro-2,2'-bithiophene (4ClBT), as CH monomers. Density functional theory (DFT) calculations reveal the high selectivity between α-CH bonds in 4FTVT, 4ClTVT, 4FBT, and 4ClBT and β-CH bonds in TIG CBr monomer. All four resulting CPs exhibit low optical bandgaps of ca. 1.20 eV and ambipolar transport characteristics with both electron and hole mobility above 0.1 cm2  V-1  s-1 as elaborated with organic thin-film transistors (OTFTs). The polymer TIG-4FTVT delivers the best device performance. With this polymer, n-channel OTFTs with electron mobility up to 1.67 cm2  V-1  s-1 and p-channel OTFTs with hole mobility up to 0.62 cm2  V-1  s-1 are fabricated by modifying source/drain electrodes with polyethylenimine ethoxylated (PEIE) and MoO3 , respectively, to selectively inject electrons and holes.

Molecular Design of Multifunctional Integrated Polymer Semiconductors with Intrinsic Stretchability, High Mobility, and Intense Luminescence

Multifunctional semiconductors integrating unique optical, electrical, mechanical, and chemical characteristics are critical to advanced and emerging manufacturing technologies. However, due to the trade-off challenges in design principles, fabrication difficulty, defects in existing materials, etc., realizing multiple functions through multistage manufacturing is quite taxing. Here, an effective molecular design strategy is established to prepare a class of multifunctional integrated polymer semiconductors. The pyridal[1,2,3]triazole-thiophene co-structured tetrapolymers with full-backbone coplanarity and considerable inter/intramolecular noncovalent interactions facilitate short-range order and excellent (re)organization capability of polymer chains, providing stress-dissipation sites in the film state. The regioregular multicomponent conjugated backbones contribute to dense packing, excellent crystallinity, high crack onset strain over 100%, efficient carrier transport with mobilities exceeding 1 cm2  V-1  s-1 , and controllable near-infrared luminescence. Furthermore, a homologous blending strategy is proposed to further enhance the color-tunable luminescent properties of polymers while effectively retaining mechanical and electrical properties. The blended system exhibits excellent field-effect mobility (µ) and quantum yield (Φ), reaching a record Φ · µ of 0.43 cm2  V-1  s-1 . Overall, the proposed strategy facilitates a rational design of regioregular semicrystalline intrinsically stretchable polymers with high mobility and color-tunable intense luminescence, providing unique possibilities for the development of multifunctional integrated semiconductors in organic optoelectronics.

Conjugated Polymers from Direct Arylation Polycondensation of 3,4-Difluorothiophene-Substituted Aryls: Synthesis and Properties

3,4-Difluorothiophene-substituted aryls, i.e., 1,4-bis(3,4-difluorothiophen-2-yl)-benzene (Ph-2FTh), 1,4-bis(3,4-difluorothiophen-2-yl)-2,5-difluorobenzene (2FPh-2FTh), and 4,7-bis(3,4-difluorothiophen-2-yl)-2,1,3-benzothiadiazole (BTz-2FTh), are synthesized as C─H monomers for the synthesis of conjugated polymers (CPs) via direct arylation polycondensation (DArP) with diketopyrrolopyrrole (DPP) and isoindigo (IID) derivatives as C─Br monomers. The Gibbs free energies of activation for direct arylation (ΔG298 K , kcal mol-1 ) for α─C─H bonds of thiophene moieties as calculated by density functional theory (DFT) are 14.3, 16.5, and 16.4 kcal mol-1 for Ph-2FTh, 2FPh-2FTh and BTz-2FTh, respectively, meaning that inserting an electron-deficient unit in 3,3',4,4'-tetrafluoro-2,2'-bithiophene (4FBT, ΔG298K : 14.6 kcal mol-1 ) may cause a reactivity decrease of the C─H monomers. Photophysical and semiconducting properties of the resulting six CPs (i.e., DPP-Ph, DPP-2FPh, DPP-BTz, 2FIID-Ph, 2FIID-2FPh, and 2FIID-BTz) are characterized in detail. DPP-based CPs show ambipolar transport properties while IID-based ones exhibited n-type behavior owing to the deeper frontier molecular orbital energy levels of IID-based CPs. With source/drain electrodes modified with polyethylenimine ethoxylated, n-channel organic thin-film transistors with maximum electron mobility of 0.40, 0.54, 0.29, 0.05, 0.16, and 0.01 cm2 V-1 s-1 for DPP-Ph, DPP-2FPh, DPP-BTz, 2FIID-Ph, 2FIID-2FPh, and 2FIID-BTz, respectively, are fabricated. DPP-2FPh exhibits the best device performance due to the good film morphology and the highest intermolecular packing order.

Approaching Theoretical Limits in the Performance of Printed P-Type CuI Transistors via Room Temperature Vacancy Engineering

Development of a novel high performing inorganic p-type thin film transistor could pave the way for new transparent electronic devices. This complements the widely commercialized n-type counterparts, indium-gallium-zinc-oxide (IGZO). Of the few potential candidates, copper monoiodide (CuI) stands out. It boasts visible light transparency and high intrinsic hole mobility (>40 cm2 V-1 s-1 ), and is suitable for various low-temperature processes. However, the performance of reported CuI transistors is still below expected mobility, mainly due to the uncontrolled excess charge- and defect-scattering from thermodynamically favored formation of copper and iodine vacancies. Here, a solution-processed CuI transistor with a significantly improved mobility is reported. This enhancement is achieved through a room-temperature vacancy-engineering processing strategy on high-k dielectrics, sodium-embedded alumina. A thorough set of chemical, structural, optical, and electrical analyses elucidates the processing-dependent vacancy-modulation and its corresponding transport mechanism in CuI. This encompasses defect- and phonon-scattering, as well as the delocalization of charges in crystalline domains. As a result, the optimized CuI thin film transistors exhibit exceptionally high hole mobility of 21.6 ± 4.5 cm2 V-1 s-1 . Further, the successful operation of IGZO-CuI complementary logic gates confirms the applicability of the device.

Self-Organized Phase-Composite Nanocrystal Solids with Superior Charge Transport

Interparticle electronic coupling is essential for self-assembled colloidal nanocrystal (NC) solid semiconductors to fulfill their wide-tunable electrical and optoelectrical properties, but it has been limited by disorders. Here, a disorder-tolerant coupling approach is presented by synthesizing self-organized NC solids based on amorphous/nanocrystalline phase-composites. The ZnO amorphous matrix, which infills the space between the less regularly ordered ZnO NCs, enables robust electronic coupling between neighboring NCs via the resonant wave function overlap, leading to a disorder-tolerant resonant conducting state. Field-effect transistors based on phase-composite semiconductors show delocalized band-like transport with superior field-effect mobility values (∼75 cm2 V-1 s-1), compared to amorphous or polycrystalline ZnO semiconductors. Furthermore, the broad amorphous matrix can mitigate interfacial defects between crystalline regions through atomic relaxation, in contrast to narrow grain boundaries in polycrystalline films, resulting in a significantly low interface trap density for phase-composite NC solids. Density function theory calculations and quantum transport simulations using the nonequilibrium Green's function formalism elucidate the origins of superior and highly disorder-tolerant electron transport in phase-composite NC solids. Our report introduces a new class of NC solids complementary to the colloidal counterpart and will be applicable to CMOS-compatible emerging device technologies.

Facile Blending Strategy for Boosting the Conjugated Polymer Semiconductor Transistor's Mobility

The optimization of field-effect mobility in polymer field-effect transistors (FETs) is a critical parameter for advancing organic electronics. Today, many challenges still persist in understanding the roles of the design and processing of semiconducting polymers toward electronic performance. To address this, a facile approach to solution processing using blends of PDPP-TVT and PTPA-3CN is developed, resulting in a 3.5-fold increase in hole mobility and retained stability in electrical performance over 3 cm2 V-1 s-1 after 20 weeks. The amorphous D-A conjugated structure and strong intramolecular polarity of PTPA-3CN are identified as major contributors to the observed improvements in mobility. Additionally, the composite analysis by X-ray photoelectron spectroscopy (XPS) and the flash differential scanning calorimetry (DSC) technique showed a uniform distribution and was well mixed in binary polymer systems. This mobility enhancement technique has also been successfully applied to other polymer semiconductor systems, offering a new design strategy for blending-type organic transistor systems. This blending methodology holds great promise for the practical applications of OFETs.

The Effect of Alkyl Chain Length in Organic Semiconductor and Surface Polarity of Polymer Dielectrics in Organic Thin-Film Transistors (OTFTs)

The interface between dielectric and organic semiconductor is critically important in determining organic thin-film transistor (OTFT) performance. Surface polarity of the dielectric layer can hinder charge transport characteristics, which has restricted utilization of polymeric dielectric materials containing polar functional groups. Herein, the electrical characteristics of OTFTs are analyzed depending on the alkyl chain length of organic semiconductors and surface polarity of polymer dielectrics. High-performance dibenzothiopheno[6,5-b:6',5'-f]thieno[3,2-b]thiophene (DBTTT) and newly synthesized its alkylated derivatives (C6-DBTTT and C10-DBTTT) are utilized as organic semiconductors. As dielectric layers, non-polar poly(1,3,5-trimethyl-1,3,5-trivinylcyclitrisiloxane) (pV3D3) and poly(2-cyanoethyl acrylate-co-diethylene glycol divinyl ether) [p(CEA-co-DEGDVE)] with polar cyanide functionality are utilized. The fabricated OTFTs with pV3D3 commonly exhibit the excellent charge transport characteristics. In addition, the OTFT performance is improved with lengthening the alkyl chain in organic semiconductors, which can be attributed to the molecular orientation of semiconductors. On the other hand, non-alkylated DBTTT OTFTs with polar p(CEA-co-DEGDVE) show relatively poor electrical characteristics, while their performance is drastically enhanced with the alkylated DBTTTs. The ultraviolet photoelectron spectroscopy (UPS) reveals that surface polarity of the dielectric layer can be abated with alkyl chain in organic semiconductors. It is believed that this study can provide a useful insight to optimize dielectric/semiconductor interface to achieve high-performance OTFTs.

Asymmetrically Functionalized Electron-Deficient π-Conjugated System for Printed Single-Crystalline Organic Electronics

Large-area single-crystalline thin films of n-type organic semiconductors (OSCs) fabricated via solution-processed techniques are urgently demanded for high-end electronics. However, the lack of molecular designs that concomitantly offer excellent charge-carrier transport, solution-processability, and chemical/thermal robustness for n-type OSCs limits the understanding of fundamental charge-transport properties and impedes the realization of large-area electronics. The benzo[de]isoquinolino[1,8-gh]quinolinetetracarboxylic diimide (BQQDI) π-electron system with phenethyl substituents (PhC2 -BQQDI) demonstrates high electron mobility and robustness but its strong aggregation results in unsatisfactory solubility and solution-processability. In this work, an asymmetric molecular design approach is reported that harnesses the favorable charge transport of PhC2 -BQQDI, while introducing alkyl chains to improve the solubility and solution-processability. An effective synthetic strategy is developed to obtain the target asymmetric BQQDI (PhC2 -BQQDI-Cn ). Interestingly, linear alkyl chains of PhC2 -BQQDI-Cn (n = 5-7) exhibit an unusual molecular mimicry geometry with a gauche conformation and resilience to dynamic disorders. Asymmetric PhC2 -BQQDI-C5 demonstrates excellent electron mobility and centimeter-scale continuous single-crystalline thin films, which are two orders of magnitude larger than that of PhC2 -BQQDI, allowing for the investigation of electron transport anisotropy and applicable electronics.

Progress, Challenges, and Opportunities in Oxide Semiconductor Devices: A Key Building Block for Applications Ranging from Display Backplanes to 3D Integrated Semiconductor Chips

As Si has faced physical limits on further scaling down, novel semiconducting materials such as 2D transition metal dichalcogenides and oxide semiconductors (OSs) have gained tremendous attention to continue the ever-demanding downscaling represented by Moore's law. Among them, OS is considered to be the most promising alternative material because it has intriguing features such as modest mobility, extremely low off-current, great uniformity, and low-temperature processibility with conventional complementary-metal-oxide-semiconductor-compatible methods. In practice, OS has successfully replaced hydrogenated amorphous Si in high-end liquid crystal display devices and has now become a standard backplane electronic for organic light-emitting diode displays despite the short time since their invention in 2004. For OS to be implemented in next-generation electronics such as back-end-of-line transistor applications in monolithic 3D integration beyond the display applications, however, there is still much room for further study, such as high mobility, immune short-channel effects, low electrical contact properties, etc. This study reviews the brief history of OS and recent progress in device applications from a material science and device physics point of view. Simultaneously, remaining challenges and opportunities in OS for use in next-generation electronics are discussed.

Multifunctional Crystalline InGaSnO Phototransistor Exhibiting Photosensing and Photosynaptic Behavior Using Oxygen Vacancy Engineering

A multifunctional optoelectronic device implementing photodetector, photosynapse, and photomemory is of increasing attention for neuromorphic system. This enables multiple devices to be replaced with a single device, which simplifies the structure of complex, highly integrated electronics. Here, a multifunctional c-axis-aligned crystalline indium gallium tin oxide thin-film transistor (TFT) optoelectronic device is demonstrated. The photodetecting and photosynaptic behaviors could be demonstrated by tuning of gate pulse. The device shows a high responsivity of 1.1 × 106  A W-1 to blue light (467 nm) and cutoff frequency (f-3dB ) of 2400 Hz exhibiting high frequency switching using a gate reset pulse. It is possible to implement photosynaptic behavior using persistent photoconductivity effect by applying a gate bias to make the TFT depletion mode. When potentiation and depression of synaptic weight are implemented with light pulse and gate voltage pulse, respectively, 64-state potentiation-depression curves are demonstrated with excellent nonlinearity of 1.13 and 2.03, respectively. When an artificial neural network is constructed with this device for the Modified National Institute of Standards and Technology training pattern recognition simulation, it shows a high pattern recognition accuracy of 90.4%.

Achieving ideal transistor characteristics in conjugated polymer semiconductors

Organic thin-film transistors (OTFTs) with ideal behavior are highly desired, because nonideal devices may overestimate the intrinsic property and yield inferior performance in applications. In reality, most polymer OTFTs reported in the literature do not exhibit ideal characteristics. Supported by a structure-property relationship study of several low-disorder conjugated polymers, here, we present an empirical selection rule for polymer candidates for textbook-like OTFTs with high reliability factors (100% for ideal transistors). The successful candidates should have low energetic disorder along their backbones and form thin films with spatially uniform energetic landscapes. We demonstrate that these requirements are satisfied in the semicrystalline polymer PffBT4T-2DT, which exhibits a reliability factor (~100%) that is exceptionally high for polymer devices, rendering it an ideal candidate for OTFT applications. Our findings broaden the selection of polymer semiconductors with textbook-like OTFT characteristics and would shed light upon the molecular design criteria for next-generation polymer semiconductors.

Modification of Two-Dimensional Tin-Based Perovskites by Pentanoic Acid for Improved Performance of Field-Effect Transistors

Understanding and controlling the nucleation and crystallization in solution-processed perovskite thin films are critical to achieving high in-plane charge carrier transport in field-effect transistors (FETs). This work demonstrates a simple and effective additive engineering strategy using pentanoic acid (PA). Here, PA is introduced to both modulate the crystallization process and improve the charge carrier transport in 2D 2-thiopheneethylammonium tin iodide ((TEA)₂ SnI₄ ) perovskite FETs. It is revealed that the carboxylic group of PA is strongly coordinated to the spacer cation TEAI and [SnI₆ ]^4- framework in the perovskite precursor solution, inducing heterogeneous nucleation and lowering undesired oxidation of Sn²⁺ during the film formation. These factors contribute to a reduced defect density and improved film morphology, including lower surface roughness and larger grain size, resulting in overall enhanced transistor performance. The reduced defect density and decreased ion migration lead to a higher p-channel charge carrier mobility of 0.7 cm² V^-1 s^-1 , which is more than a threefold increase compared with the control device. Temperature-dependent charge transport studies demonstrate a mobility of 2.3 cm² V^-1 s^-1 at 100 K due to the diminished ion mobility at low temperatures. This result illustrates that the additive strategy bears great potential to realize high-performance Sn-based perovskite FETs.

Synaptic plasticity realized by selective oxidation of TiS3 nanosheet for neuromorphic devices

Memristive devices operating analogous to biology synapses demonstrate great potential for neuromorphic applications. Here, we reported the space-confined vapor synthesis of ultrathin titanium trisulfide (TiS₃) nanosheets, and subsequent laser manufacturing of a TiS₃-TiO_x-TiS₃ in-plane heterojunction for memristor applications. Due to the flux-controlled migration and aggregation of oxygen vacancies, the two-terminal memristor demonstrates reliable "analog" switching behaviors, in which the channel conductance can be incrementally adjusted by tuning the duration and sequence of programming voltage. The device allows the emulation of basic synaptic functions, featuring excellent linearity and symmetry in conductance change during long-term potentiation/depression processes. The small asymmetric ratio of 0.15 enables it to be integrated into a neural network for the pattern recognition task with a high accuracy of 90%. The results demonstrate the great potential of TiS₃-based synaptic devices for neuromorphic applications.

Self-Doping Naphthalene Diimide Conjugated Polymers for Flexible Unipolar n-Type OTFTs

The development of high-performance organic thin-film transistor (OTFT) materials is vital for flexible electronics. Numerous OTFTs are so far reported but obtaining high-performance and reliable OTFTs simultaneously for flexible electronics is still challenging. Herein, it is reported that self-doping in conjugated polymer enables high unipolar n-type charge mobility in flexible OTFTs, as well as good operational/ambient stability and bending resistance. New naphthalene diimide (NDI)-conjugated polymers PNDI2T-NM17 and PNDI2T-NM50 with different contents of self-doping groups on their side chains are designed and synthesized. The effects of self-doping on the electronic properties of resulting flexible OTFTs are investigated. The results reveal that the flexible OTFTs based on self-doped PNDI2T-NM17 exhibit unipolar n-type charge-carrier properties and good operational/ambient stability thanks to the appropriate doping level and intermolecular interactions. The charge mobility and on/off ratio are fourfold and four orders of magnitude higher than those of undoped model polymer, respectively. Overall, the proposed self-doping strategy is useful for rationally designing OTFT materials with high semiconducting performance and reliability.

Improving Environmental and Operational Stability of Polymer Field-Effect Transistors by Doping with Tetranitrofluorenone

Operational instability of organic field-effect transistors (OFETs) is one of the key limitations for applications of printed electronics. Environmental species, especially oxygen and water, unintentionally introduced in the OFET channel, can act as either dopants or traps for charge carriers, affecting the electrical characteristics and stability of devices. Here, we report that intentional doping of the benchmark p-type semiconducting polymer (DPP-DTT) with 2,4,5,7-tetranitrofluorenone (TeNF) markedly improves the operational and environmental stability of OFETs. Electrical interrogation of DPP-DTT OFETs in various environments and at variable temperatures shows suppression of electron-induced traps and increase of hole mobility in oxygen-rich environment, while the water molecules act as traps for positive charge carrier, reducing the hole mobility and significantly shifting the threshold voltage. Doping of DPP-DTT with TeNF suppresses both effects, resulting in environmentally independent performance and superior long-term stability of unencapsulated devices for up to 4 months in ambient air. Furthermore, the doped OFETs exhibit dramatically reduced hysteresis and bias-stressed current drop. Such improvement of the environmental and operational stabilities is ascribed to the mitigation of traps induced by the injected minority carrier (electrons) and the reduction of the majority carrier (hole) traps in doped polymer films due to enhanced microstructural order.

Disordered Phase-Assisted Growth of Organic Semiconductor Crystals on Self-Assembled Monolayer Templates

Achieving high mobility and bias stability is a challenging obstacle in the advancement of organic thin-film transistors (OTFTs). To this end, the fabrication of high-quality organic semiconductor (OSC) thin films is critical for OTFTs. Self-assembled monolayers (SAMs) have been used as growth templates for high-crystalline OSC thin films. Despite significant research progress in the growth of OSC on SAMs, a detailed understanding of the growth mechanism of the OSC thin films on a SAM template is lacking, which has limited its use. In this study, the effects of the structure (thickness and molecular packing) of SAM on the nucleation and growth behavior of the OSC thin films were investigated. We found that disordered SAM molecules assisted in the surface diffusion of the OSC molecules and resulted in a small nucleation density and large grain size of the OSC thin films. Moreover, a thick SAM with disordered SAM molecules on the top was found to be beneficial for the high mobility and bias stability of the OTFTs.

Homogeneously Oriented Organic Single-Crystalline Patterns Grown by Microspacing In-Air Sublimation

Fabrication of single-crystalline organic semiconductor patterns is of key importance to enable practical applications. However due to the poor controllability on nucleation locations and the intrinsic anisotropic nature of single-crystals, growth of single-crystal patterns with homogeneous orientation is a big challenge especially by the vapor method. Herein a vapor growth protocol to achieve patterned organic semiconductor single-crystals with high crystallinity and uniform crystallographic orientation is presented. The protocol relies on the recently invented microspacing in-air sublimation assisted with surface wettability treatment to precisely pin the organic molecules at desired locations, and inter-connecting pattern motifs to induce homogeneous crystallographic orientation. Single-crystalline patterns with different shapes and sizes, and uniform orientation are demonstrated exemplarily by using 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT). Field-effect transistor arrays fabricate on the patterned C8-BTBT single-crystal patterns show uniform electrical performance: a 100% yield with an average mobility of 6.28 cm²  V^-1  s^-1 and in a 5 × 8 array. The developed protocols overcome the uncontrollability of the isolated crystal patterns in vapor growth on non-epitaxial substrates, making it possible to align the anisotropic electronic nature of single-crystal patterns in large-scale devices integration.

Improving OFF-State Bias-Stress Stability in High-Mobility Conjugated Polymer Transistors with an Antisolvent Treatment

Conjugated polymer field-effect transistors are emerging as an enabling technology for flexible electronics due to their excellent mechanical properties combined with sufficiently high charge-carrier mobilities and compatibility with large-area, low-temperature processing. However, their electrical stability remains a concern. ON-state (accumulation mode) bias-stress instabilities in organic semiconductors have been widely studied, and multiple mitigation strategies have been suggested. In contrast, OFF-state (depletion mode) bias-stress instabilities remain poorly understood despite being crucial for many applications in which the transistors are held in their OFF-state for most of the time. Here, a simple method of using an antisolvent treatment is presented to achieve significant improvements in OFF-state bias-stress and environmental stability as well as general device performance for one of the best performing polymers, solution-processable indacenodithiophene-co-benzothiadiazole (IDT-BT). IDT-BT is weakly crystalline, and the notable improvements to an antisolvent-induced, increased degree of crystallinity, resulting in a lower probability of electron trapping and the removal of charge traps is attributed. The work highlights the importance of the microstructure in weakly crystalline polymer films and offers a simple processing strategy for achieving the reliability required for applications in flexible electronics.

Intrinsically Stretchable Polymer Semiconductors with Good Ductility and High Charge Mobility through Reducing the Central Symmetry of the Conjugated Backbone Units

Intrinsically stretchable polymer semiconductors are highly demanding for flexible electronics. However, it still remains challenging to achieve synergy between intrinsic stretchability and charge transport property properly for polymer semiconductors. In this paper, terpolymers are reported as intrinsically stretchable polymeric semiconductors with good ductility and high charge mobility simultaneously by incorporation of non-centrosymmetric spiro[cycloalkane-1,9'-fluorene] (spiro-fluorene) units into the backbone of diketopyrrolopyrrole (DPP) based conjugated polymers. The results reveal that these terpolymers show obviously high crack onset strains and their tensile moduli are remarkably reduced, by comparing with the parent DPP-based conjugated polymer without spiro-fluorene units. They exhibit simultaneously high charge mobilities (>1.0 cm² V^-1 s^-1 ) at 100% strain and even after repeated stretching and releasing cycles for 500 times under 50% strain. The terpolymer P2, in which cyclopropane is linked to the spiro-fluorene unit, is among the best reported intrinsically stretchable polymer semiconductors with record mobility up to 3.1 cm² V^-1 s^-1 at even 150% strain and 1.4 cm² V^-1 s^-1 after repeated stretching and releasing cycles for 1000 times.

Recent advances in n-type and ambipolar organic semiconductors and their multi-functional applications

Organic semiconductors have received broad attention and research interest due to their unique integration of semiconducting properties with structural tunability, intrinsic flexibiltiy and low cost. In order to meet the requirements of organic electronic devices and their integrated circuits, p-type, n-type and ambipolar organic semiconductors are all necessary. However, due to the limitation in both material synthesis and device fabrication, the development of n-type and ambipolar materials is quite behind that of p-type materials. Recent development in synthetic methods of organic semiconductors greatly enriches the range of n-type and ambipolar materials. Moreover, the newly developed materials with multiple functions also put forward multi-functional device applications, including some emerging research areas. In this review, we give a timely summary on these impressive advances in n-type and ambipolar organic semiconductors with a special focus on their synthesis methods and advanced materials with enhanced properties of charge carrier mobility, integration of high mobility and strong emission and thermoelectric properties. Finally, multi-functional device applications are further demonstrated as an example of these developed n-type and ambipolar materials.

Soft Fiber Electronics Based on Semiconducting Polymer

Fibers, originating from nature and mastered by human, have woven their way throughout the entire history of human civilization. Recent developments in semiconducting polymer materials have further endowed fibers and textiles with various electronic functions, which are attractive in applications such as information interfacing, personalized medicine, and clean energy. Owing to their ability to be easily integrated into daily life, soft fiber electronics based on semiconducting polymers have gained popularity recently for wearable and implantable applications. Herein, we present a review of the previous and current progress in semiconducting polymer-based fiber electronics, particularly focusing on smart-wearable and implantable areas. First, we provide a brief overview of semiconducting polymers from the viewpoint of materials based on the basic concepts and functionality requirements of different devices. Then we analyze the existing applications and associated devices such as information interfaces, healthcare and medicine, and energy conversion and storage. The working principle and performance of semiconducting polymer-based fiber devices are summarized. Furthermore, we focus on the fabrication techniques of fiber devices. Based on the continuous fabrication of one-dimensional fiber and yarn, we introduce two- and three-dimensional fabric fabricating methods. Finally, we review challenges and relevant perspectives and potential solutions to address the related problems.

A guide for the characterization of organic electrochemical transistors and channel materials

The organic electrochemical transistor (OECT) is one of the most versatile devices within the bioelectronics toolbox, with its compatibility with aqueous media and the ability to transduce and amplify ionic and biological signals into an electronic output. The OECT operation relies on the mixed (ionic and electronic charge) conduction properties of the material in its channel. With the increased popularity of OECTs in bioelectronics applications and to benchmark mixed conduction properties of channel materials, the characterization methods have broadened somewhat heterogeneously. We intend this review to be a guide for the characterization methods of the OECT and the channel materials used. Our review is composed of two main sections. First, we review techniques to fabricate the OECT, introduce different form factors and configurations, and describe the device operation principle. We then discuss the OECT performance figures of merit and detail the experimental procedures to obtain these characteristics. In the second section, we shed light on the characterization of mixed transport properties of channel materials and describe how to assess films' interactions with aqueous electrolytes. In particular, we introduce experimental methods to monitor ion motion and diffusion, charge carrier mobility, and water uptake in the films. We also discuss a few theoretical models describing ion-polymer interactions. We hope that the guidelines we bring together in this review will help researchers perform a more comprehensive and consistent comparison of new materials and device designs, and they will be used to identify advances and opportunities to improve the device performance, progressing the field of organic bioelectronics.

A Hybrid Acceptor-Modulation Strategy: Fluorinated Triple-Acceptor Architecture for Significant Enhancement of Electron Transport in High-Performance Unipolar n-Type Organic Transistors

The development of unipolar n-type semiconducting polymers with electron mobility (µ_e ) over 5 cm²  V^-1  s^-1 remains a massive challenge in organic semiconductors. Diketopyrrolopyrrole (DPP) has proven to be a successful unit for high-performance p-type and ambipolar polymers. However, DPP's moderate electron-accepting capability leads to the shallow frontier molecular orbital (FMO) levels of the resultant polymers and hence limit the µ_e in unipolar n-type organic transistors. Herein, this issue has been addressed by using a hybrid acceptor-modulation strategy based on DPP-containing "fluorinated triple-acceptor architecture", namely DPP-difluorobenzothiadiazole-DPP (DFB). Compared with DFB's non-fluorinated counterpart, DFB features deeper FMO levels and a shape-persistent framework. Therefore, a series of DFB-based polymers demonstrate planar backbones and lowered FMO levels by ≈0.10 to 0.25 eV versus that of the control polymer. Intriguingly, all DFB-polymers exhibit excellent unipolar n-type transistor performances. Notably, a full-locked backbone conformation and high crystallinity with crystalline coherence length of 524 Å are observed for pDFB-TF, accounting for its high µ_e of 5.04 cm²  V^-1  s^-1 , which is the highest µ_e value for DPP-based unipolar n-type polymers reported to date. This work demonstrates that the strategy of "fluorinated triple-acceptor architecture" opens a new path towards high-performance unipolar n-type semiconducting polymers.

Charge transport in mixed metal halide perovskite semiconductors

Investigation of the inherent field-driven charge transport behaviour of three-dimensional lead halide perovskites has largely remained challenging, owing to undesirable ionic migration effects near room temperature and dipolar disorder instabilities prevalent specifically in methylammonium-and-lead-based high-performing three-dimensional perovskite compositions. Here, we address both these challenges and demonstrate that field-effect transistors based on methylammonium-free, mixed metal (Pb/Sn) perovskite compositions do not suffer from ion migration effects as notably as their pure-Pb counterparts and reliably exhibit hysteresis-free p-type transport with a mobility reaching 5.4 cm² V^-1 s^-1. The reduced ion migration is visualized through photoluminescence microscopy under bias and is manifested as an activated temperature dependence of the field-effect mobility with a low activation energy (~48 meV) consistent with the presence of the shallow defects present in these materials. An understanding of the long-range electronic charge transport in these inherently doped mixed metal halide perovskites will contribute immensely towards high-performance optoelectronic devices.

Impact of Narrowing Density of States in Semiconducting Polymers on Performance of Organic Field-Effect Transistors

To improve the performance of organic field-effect transistors (OFETs) employing π-conjugated polymers, a basic understanding of the relationships between the material properties and device characteristics is crucial. Although the density of states (DOS) distribution is one of the essential material properties of semiconducting polymers, insights into how the DOS shape affects the mobility (µ), subthreshold swing (S), and contact resistance (R_C ) in OFETs remain lacking. In this study, by combining sensitive DOS measurements and multilayered OFET structures, it is experimentally demonstrated that narrower DOS widths in the polymer channels lead to higher µ, smaller S, and lower R_C . By contrast, variation of the DOS in the bulk layer does not affect the performance. These results demonstrate a direct relationship between the polymer properties and OFET performance and highlight the importance of controlling the DOS width in π-conjugated polymers.

Nanoscale Mapping of Carrier Mobilities in the Ballistic Transports of Carbon Nanotube Networks

Much progress has been made in the nanoscale analysis of nanostructures, while the mapping of key charge transport properties such as a carrier mobility remains a challenge, especially for one-dimensional systems. Here, we report the nanoscale mapping of carrier mobilities in carbon nanotube (CNT) networks and show that charge transport behaviors varied depending on network structures. In this work, the spatial distribution of localized charge transport properties such as mobilities and charge trap densities in CNT networks were mapped via a scanning noise microscopy. The mobility map was obtained from the conductivity maps measured at different back-gate biases, showing up to two orders of mobility variations depending on localized network structures. Furthermore, from the maps, correlations between mobility/conductivity and charge trap density were analyzed to determine charge transport mechanisms. In metallic CNT networks, the regions with rather high (low) or low (high) charge trap densities (mobilities) exhibited a diffusive or ballistic transport behavior, respectively. Interestingly, semiconducting CNT networks also exhibited a gradual transition from a diffusive to a ballistic transport behavior as the CNT mobility was increased by reaching the on-state with negative gate biases. The mapping of the cross-patterned CNT network showed that metallic CNT electrodes could achieve a good electrical contact with semiconducting CNTs without high contact resistance regions. Since this method allowed one to map versatile charge transport properties such as mobility, conductivity, and charge trap density, it can be a powerful tool for basic research about charge transport phenomena and practical device applications.

Mechanically robust stretchable semiconductor metallization for skin-inspired organic transistors

Despite recent remarkable advances in stretchable organic thin-film field-effect transistors (OTFTs), the development of stretchable metallization remains a challenge. Here, we report a highly stretchable and robust metallization on an elastomeric semiconductor film based on metal-elastic semiconductor intermixing. We found that vaporized silver (Ag) atom with higher diffusivity than other noble metals (Au and Cu) forms a continuous intermixing layer during thermal evaporation, enabling highly stretchable metallization. The Ag metallization maintains a high conductivity (>10⁴ S/cm) even under 100% strain and successfully preserves its conductivity without delamination even after 10,000 stretching cycles at 100% strain and several adhesive tape tests. Moreover, a native silver oxide layer formed on the intermixed Ag clusters facilitates efficient hole injection into the elastomeric semiconductor, which transcends previously reported stretchable source and drain electrodes for OTFTs.

The Radical Anion, Dianion and Electron Transport Properties of Tetraiodotetraazapentacene

Tetraiodotetraazapentacene I₄ TAP, the last missing derivative in the series of halogenated silylated tetraazapentacenes, was synthesized via condensation chemistry from a TIPS-ethynylated diaminobenzothiadiazol in three steps. Single and double reduction furnished its air-stable monoanion and relatively air-stable dianion, both of which were characterized by crystallography. All three species are structurally and spectroscopically compared to non-halogenated TAP and Br₄ TAP. I₄ TAP is an n-channel material in thin-film transistors with average electron mobilities exceeding 1 cm² (Vs)^-1 .