Water-Surface-Mediated Precise Patterning of Organic Single-Crystalline Films via Double-Blade Coating for High-Performance Organic Transistors

Application-oriented growth of patterned organic semiconductor (OSC) thin films with a single domain is a nonnegotiable requirement for the manufacturing of high-performance organic electronic devices. However, the prevalent selective-wetting patterning method remains a challenge in controlling the density of nucleation events in microscale spaces, resulting in thin films with high grain boundary density and no preferential orientation spherulites. Herein, a simple double-blade-coating printing technique using a combination of wetting-patterned substrates to produce an array of highly crystalline OSC thin films is developed. Specifically, the approach confines the OSC crystallization on a molecular-flat water surface in specific areas, enabling a significant reduction in the number of nuclei. Consequently, patterned 2,7-dioctyl[1]benzothieno[3,2-b] benzothiophene (C₈-BTBT) thin films comprising single-crystal domains are achieved with an exceptionally high yield of 62.5%. The organic field-effect transistor array developed from such patterns of C₈-BTBT single-crystalline films exhibits an excellent average mobility of 11.5 cm² V⁻¹ s⁻¹ which is 12.5-fold higher compared to that of the reference sample fabricated via conventional single-blade coating. It is believed that this approach can be widely applied to other soluble organic materials, thereby opening up opportunities for fabricating multicomponent integrated electronics.     

Wafer-Scale Growth of Aligned C60 Single Crystals via Solution-Phase Epitaxy for High-Performance Transistors

Fullerene (C₆₀) single crystals with exceptionally low defects and nearly perfect translational symmetry make them appealing in achieving high-performance n-type organic transistors. However, because of its natural 0D structure, control over continuous crystallization of C₆₀ over a large area is extremely challenging. Here, the authors report a solution-phase epitaxial approach for wafer-scale growth of continuously aligned C₆₀ single crystals. This method enables the rational control of the density of nucleation event at meniscus front by confining the size and shape of meniscus with a microchannel template. In this case, a single nucleus as seed crystal can be formed at the front of meniscus, and then epitaxial growth from the seed crystal occurs with continuous retreat of the meniscus. As a result, highly uniform C₆₀ single-crystal array with ultralow defect density is obtained on 2-inch substrate. Organic field-effect transistors made from the C₆₀ single-crystal array show a high average electron mobility of 2.17 cm² V⁻¹ s⁻¹, along with a maximum mobility of 5.09 cm² V⁻¹ s⁻¹, which is much superior to the C₆₀ polycrystalline film-based devices. This strategy opens new opportunities for the scalable fabrication of high-performance integrated devices based on organic crystals.     

Solutal-Marangoni-Flow-Mediated Growth of Patterned Highly Crystalline Organic Semiconductor Thin Film Via Gap-Controlled Bar Coating

Application-oriented patterned growth of organic semiconductor (OSC) thin films with single crystalline domains is crucial for fabricating sophisticated high-performance organic-electronic and optoelectronic devices; however, fabricating these patterned nanometer-thick crystals in a simple, fast, and effective manner is a difficult task with a roll-to-roll printing process. Here, a simple bar-coating approach to form an array of single-crystal-like OSC thin-film patterns at a rate of a few millimeters per second is introduced. To this end, the processing parameters of a gap-controlled bar-coating method is optimized, including coating speed, crystal nucleation, and solution fluidics, which allow a high degree of morphological control of bar-coated OSC films in an area of several centimeters. In particular, it is demonstrated that the solutal-Marangoni flow induced by a suitable solvent additive can considerably improve molecular mass transport and induce favorable vertical phase separation. Thus, organic transistors based on the OSC patterns fabricated with the additive-assisted bar coating show a field-effect mobility of up to 20 cm² V⁻¹ s⁻¹ and superior operational stability. The proposed bar coating method will facilitate an industry-level application of organic electronics.     

Controllable thin-film morphology and structure for 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8BTBT) based organic field-effect transistors

Organic field-effect transistors (OFETs) based on organic semiconductor material 2,7-dioctyl[1]benzothieno[3,2-b] benzothiophene (C8BTBT) as the active layer were fabricated by using organic molecular beam deposition (OMBD) and solution-processed methods, in which the C8BTBT thin-film morphology could be well controlled. In OMBD method, C8BTBT thin-film morphology could be controlled by the thickness of organic semiconductor layer and the deposition rate, of which the high-quality C8BTBT thin film was obtained at a thickness of about 20 nm and at a deposition rate of 1.2 nm/min, resulting in an obvious mobility improvement from 2.8 × 10⁻³ cm² V⁻¹ s⁻¹ to 1.20 cm² V⁻¹ s⁻¹. While in the solution-processing, C8BTBT thin-film morphology and thickness are related to the spin-coating speed and the substrate position in spin coater, i.e., in-centre and off-centre position. The off-centre spin-coating with an optimized speed produced large-size domain C8BTBT thin film and accordingly resulted in a mobility of 1.47 cm² V⁻¹ s⁻¹. Furthermore, an additive polystyrene (PS) was added into C8BTBT solution could further improve the thin-film morphology with more metal-stable phase as well as improve the interface contact with the substrate SiO₂, resulting in the highest mobility up to 3.56 cm² V⁻¹ s⁻¹. The research suggested that C8BTBT-based OFETs with the mobility over 1.20 cm² V⁻¹ s⁻¹ could be fabricated by using both OMBD and solution-processed methods through the thin-film morphology and structure optimization, which shows the potential applications in high-performance flexible and printed electronics.     

Effects of gate dielectric surface modification on phototransistors with polymer-blended benzothieno[2,3-b]benzothiophene semiconductor thin films

In the present work, we investigated effects of the dielectric/semiconductor interface modification on the photoelectrical properties of phototransistors comprising a UV responsive semiconductor blend 2,7-dipentyl-[1]benzothieno[2,3-b][1]benzothiophene (C5-BTBT) and a linear unsaturated polyester (L-upe). Using various self-assembly monolayers with different end-groups at the dielectric/semiconductor interface we modulated the drain photocurrent and response times under the UV light illumination of phototransistors. Treatment of the SiO₂ dielectric surface with organosilanes led to the variation of the max mobility in the dark 0.10–0.18 cm² V⁻¹ s⁻¹ and under UV light 0.08–0.50 cm² V⁻¹ s⁻¹. Interestingly, detailed crystal structure analysis using 2D X-ray diffraction and photoelectrical characterization revealed that mobility in the dark predominantly depends on the alignment of C5-BTBT crystallites at the interface. Under UV light, the mobility increased with the electron withdrawing/donating nature of the SAM end-functional group. Additionally, chemical modification of the SiO₂ dielectric surface increased photocurrent relaxation/decay times upon UV light removal while retaining fast response times when exposed to UV light, which enhanced memory properties of fabricated phototransistors (fast UV response = writing and long relaxation = long data storage).     

A Highly Crystalline Fused‐Ring n‐Type Small Molecule for Non‐Fullerene Acceptor Based Organic Solar Cells and Field‐Effect Transistors

N‐type organic small molecules (SMs) are attracting attention in the organic electronics field, due to their easy purification procedures with high yield. However, only a few reports show SMs that perform well in both organic field‐effect transistors (OFETs) and organic solar cells (OSCs). Here, the synthesis and characterization of an n‐type small molecule with an indacenodithieno[3,2‐b]thiophene (IDTT) core unit and linear alkylated side chain (C₁₆) (IDTTIC) are reported. Compared to the state‐of‐the‐art n‐type molecule IDTIC, IDTTIC exhibits smaller optical bandgap and higher absorption coefficient, which is due to the enhanced intramolecular effect. After mixing with the polymer donor PBDB‐T, IDTIC‐based solar cells deliver a power conversion efficiency of only 5.67%. In stark contrast, the OSC performance of IDTTIC improves significantly to 11.2%. It is found that the superior photovoltaic properties of PBDB‐T:IDTTIC blends are mainly due to reduced trap‐assisted recombination and enhanced molecular packing coherence length and higher domain purity when compared to IDTIC. Moreover, a significantly higher electron mobility of 0.50 cm² V⁻¹ s⁻¹ for IDTTIC in OFET devices than for IDTIC (0.15 cm² V⁻¹ s⁻¹) is obtained. These superior performances in OSCs and OFETs demonstrate that SMs with extended π‐conjugation of the backbone possess a great potential for application in organic electronic devices.     

Hall Effect in Polycrystalline Organic Semiconductors: The Effect of Grain Boundaries

Highly crystalline thin films in organic semiconductors are important for applications in high‐performance organic optoelectronics. Here, the effect of grain boundaries on the Hall effect and charge transport properties of organic transistors based on two exemplary benchmark systems is elucidated: (1) solution‐processed blends of 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene (C₈‐BTBT) small molecule and indacenodithiophene‐benzothiadiazole (C₁₆IDT‐BT) conjugated polymer, and (2) large‐area vacuum evaporated polycrystalline thin films of rubrene (C₄₂H₂₈). It is discovered that, despite the high field‐effect mobilities of up to 6 cm² V^?1 s^?1 and the evidence of a delocalized band‐like charge transport, the Hall effect in polycrystalline organic transistors is systematically and significantly underdeveloped, with the carrier coherence factor α < 1 (i.e., yields an underestimated Hall mobility and an overestimated carrier density). A model based on capacitively charged grain boundaries explaining this unusual behavior is described. This work significantly advances the understanding of magneto‐transport properties of organic semiconductor thin films.     

Interface optimization using diindenoperylene for C60 thin film transistors with high electron mobility and stability

C₆₀-based organic thin film transistors (OTFTs) with high electron mobility and high operational stability are achieved with (1 1 1) oriented C₆₀ films grown by using template effects of diindenoperylene (DIP) under layer on the SiO₂ gate insulator. The electron mobility of the C₆₀ transistor is significantly increased from 0.21 cm² V⁻¹ s⁻¹ to 2.92 cm² V⁻¹ s⁻¹ by inserting the template-DIP layer. Moreover much higher operational stability is also observed for the DIP-template C₆₀ OTFTs. A grazing incidence X-ray diffraction and ultrahigh-sensitivity photoelectron spectroscopy measurements indicate that the improved electron mobility and stability arise from the decreased density of trap states in the C₆₀ film due to increased (1 1 1) orientation of C₆₀-grains and their crystallinity on the DIP template.     

Bithienopyrroledione‐Based Copolymers,Versatile Semiconductors for Balanced Ambipolar Thin‐Film Transistors and Organic Solar Cells with V oc > 1 V

Conjugated polymer semiconductors P1 and P2 with bithienopyrroledione (bi‐TPD) as acceptor unit are synthesized. Their transistor and photovoltaic performances are investigated. Both polymers display high and balanced ambipolar transport behaviors in thin‐film transistors. P1‐ based devices show an electron mobility of 1.02 cm² V^?1 s^?1 and a hole mobility of 0.33 cm² V^?1 s^?1, one of the highest performance reported for ambipolar polymer transistors. The electron and hole mobilities of P2 transistors are 0.36 and 0.16 cm² V^?1 s^?1, respectively. The solar cells with PC₇₁BM as the electron acceptor and P1/P2 as the donor exhibit a high V _oc about 1.0 V, and a power conversion efficiency of 6.46% is observed for P1‐ based devices without any additives and/or post treatment. The high performance of P1 and P2 is attributed to their crystalline films and short π–π stacking distance (<3.5 Å). These results demonstrate (1) bi‐TPD is an excellent versatile electron‐deficient unit for polymer semiconductors and (2) bi‐TPD‐based polymer semiconductors have potential applications in organic transistors and organic solar cells.     

J-Type Self-Assembled Supramolecular Polymers for High-Performance and Fast-Response n-Type Organic Electrochemical Transistors

To date, high-performance organic electrochemical transistors (OECTs) are almost all based on conjugated polymers. Small molecules can be synthesized with high purity without batch-to-batch variations. However, small molecules require highly crystalline films and good molecular packings to achieve high charge carrier mobilities. Such features make their films unsuitable for ion diffusion or make their molecular packing distorted due to ion diffusion, resulting in poor ion/charge carrier transport properties and slow response speed. Herein, it is proposed to construct small-molecule-based supramolecular polymers to address these issues. A molecule, namely TDPP-RD-G7 is designed, which exhibits J-type self-assembling behaviors and can form supramolecular polymers in solution and conjugated-polymer-like networks in solid state. More importantly, the porous supramolecular polymer networks allow fast ion diffusion and greatly increase the device response speeds. As a result, the TDPP-RD-G7 exhibits record fast response speeds (τ_on/τ_off) of 10.5/0.32 ms with high figure-of-merit (µC*) of 5.88 F cm⁻¹ V⁻¹ s⁻¹ in small-molecule OECTs. This work reveals the possible reasons that hinder the response speeds in small-molecule OECTs and demonstrates a new “supramolecular polymer” approach to high-performance and fast-response small-molecule-based OECTs.     

Simultaneous control of molecular orientation and patterning of small-molecule organic semiconductors for organic transistors

Triethylsilylethynyl anthradithiophene (TES-ADT) has been shown to be a promising soluble semiconductor for the active layer of organic field-effect transistors (OFETs) due to its solution processability, chemical stability and excellent electrical properties. However, there are still some problems that need to be resolved for the utilization of TES-ADT in OFETs. One of these problems is a patterning issue to minimize crosstalk between neighboring TES-ADT FETs. To this end, TES-ADT crystals of various shapes need to be patterned at the desired positions. Here, we demonstrated a simple method to fabricate patterned TES-ADT crystals by using a PDMS mold containing 1,2–dichloroethane (DCE) solvent. This method serves the dual purpose of preparing a variety of pattern shapes while simultaneously changing as-spun TES-ADT thin films into crystal patterns. The top-contact OFETs with the TES-ADT crystal patterns exhibited high performance, reaching a field-effect mobility of ∼0.3 cm² V⁻¹s⁻¹.     

Solution-processed single-crystalline organic transistors on patterned ultrathin gate insulators

Single-crystalline organic transistors of 3,11-didecyl-dinaphtho[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (C₁₀-DNBDT-NW) and 2,9-didecyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C₁₀-DNTT) were fabricated by solution processes on top of the patterned hybrid ultrathin gate dielectrics consisting of 3.6 nm-thick aluminum oxide and self-assembled monolayers (SAMs). Due to the excellent crystallinity of the channel films, bottom-gate and top-contact field-effect transistors exhibited the average field-effect mobility of 3.7 cm²/V s and 4.3 cm²/V s for C₁₀-DNBDT-NW and C₁₀-DNTT, respectively. These are the first successful devices of solution-processed single-crystalline transistors on ultrathin gate dielectrics with the mobility above 1 cm²/V s, opening the way to develop low-power-consumption and high-performance printed circuits.     

Toward High Mobility Green Solvent-Processable Conjugated Polymers: A Systematic Study on Chalcogen Effect in Poly(Diketopyrrolopyrrole-alt-Terchalcogenophene)s

Nine diketopyrrolopyrrole (DPP)-based conjugated polymers (CPs), that is, poly(diketopyrrolopyrrole-alt-terchalcogenophene)s, via combinations of furanyl-(FDPP), thienyl-(TDPP), selenophenyl-DPP (SeDPP) and furan, thiophene, selenophene comonomers, are synthesized to explore the chalcogen effect on the solubility, film morphology/microstructure, and charge transport property of the resultant polymers. All polymers except for SeDPP-Se are soluble in non-chlorinated solvents such as o-xylene and tetralin. Flanking of DPP with furan in FDPP-F, FDPP-T, and FDPP-Se enables even good solubility in green solvent anisole. TDPP-Se exhibits the highest reliable hole mobility over 10 cm² V⁻¹ s⁻¹ in organic thin film transistors (OTFTs) bar-coated from o-xylene/tetralin (20/80 v/v) solution. With anisole as the processing solvent, FDPP-F-based bar-coated OTFTs displays a reliable hole mobility up to 3.50 cm² V⁻¹ s⁻¹. This is the first report on green solvent processed OTFTs with mobility above 1 cm² V⁻¹ s⁻¹. Charge transport property of all the polymers is correlated with the film morphology and microstructure that are noticeably influenced by the type and position of chalcogenophenes. The current work sheds light on the design of high mobility CPs processable with green solvents.     

Analysis of the Annealing Budget of Metal Oxide Thin-Film Transistors Prepared by an Aqueous Blade-Coating Process

Metal oxide (MO) semiconductors are widely used in electronic devices due to their high optical transmittance and promising electrical performance. This work describes the advancement toward an eco-friendly, streamlined method for preparing thin-film transistors (TFTs) via a pure water-solution blade-coating process with focus on a low thermal budget. Low temperature and rapid annealing of triple-coated indium oxide thin-film transistors (3C-TFTs) and indium oxide/zinc oxide/indium oxide thin-film transistors (IZI-TFTs) on a 300 nm SiO₂ gate dielectric at 300 °C for only 60 s yields devices with an average field effect mobility of 10.7 and 13.8 cm² V⁻¹ s⁻¹, respectively. The devices show an excellent on/off ratio (>10⁶), and a threshold voltage close to 0 V when measured in air. Flexible MO-TFTs on polyimide substrates with AlO_x dielectrics fabricated by rapid annealing treatment can achieve a remarkable mobility of over 10 cm² V⁻¹ s⁻¹ at low operating voltage. When using a longer post-coating annealing period of 20 min, high-performance 3C-TFTs (over 18 cm² V⁻¹ s⁻¹) and IZI-TFTs (over 38 cm² V⁻¹ s⁻¹) using MO semiconductor layers annealed at 300 °C are achieved.     

Crosslinked polymer-mixture gate insulator for high-performance organic thin-film transistors

In this paper, we report on the fabrication of a crosslinked polymer-mixture gate insulator for high-performance organic thin-film transistors (TFTs). We used cyanoethylated pullulan (CEP) as a crosslinkable high-k polymer matrix and poly(ethylene-alt-maleic anhydride) (PEMA) as a polymeric crosslinking agent. Because PEMA has a high number of functional groups reactive to the hydroxyl groups of CEP, the use of PEMA is effective for minimizing the amount of remaining hydroxyl groups strongly related to the large current hysteresis and high off current of the organic TFTs. To investigate the potential of the CEP-PEMA mixture as a gate insulator, we fabricated 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C₈-BTBT) TFTs. The C₈-BTBT TFT with the 60 nm-thick CEP-PEMA gate insulator showed excellent TFT performance with a field-effect mobility of 1.4 cm²/V s and an on/off ratio of 2.4 × 10⁶.     

High-performance solution-processed organic transistors with electroless-plated electrodes

Electroless-plated gold and platinum films are used as source and drain electrodes in high-performance solution-processed organic field-effect transistors (OFETs), representing a promising large-area, near-room-temperature and vacuum-free technique to form low-resistance metal-to-semiconductor interfaces in ambient atmosphere. Developing non-displacement conditions using a Pt-colloidal catalyst for soft electroless plating, the electrodes are deposited on crystallized thin films of 2,9-didecyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C₁₀-DNTT) without significant damage to the semiconductor material. The top-contact OFETs show remarkable performance, with a mobility of 6.0 cm² V^?1 s^?1. The method represents a practical fabrication technique to mass-produce circuitry arrays of nearly best-performing OFETs for the printed electronics industry.     

Addressable growth of oriented organic semiconductor ultra-thin films on hydrophobic surface by direct dip-coating

Oriented organic field-effect transistor (OFET) stripe arrays on hydrophobic substrates were fabricated by fast dip-coating technique. The addressable growth was achieved by decreasing surface energy of the channel areas with respect to the electrodes via hydrophobic treatment. The higher surface energy of the electrodes allows solution to adhere and then organic semiconductors nucleate and bridge the channels after evaporation of the solvent. Area-selective behaviour can be controlled by adjusting surface property of transistor channel, geometry features of the gold electrodes, pulling speed and evaporation atmosphere. The mechanism behind is the competition between receding of the solution and evaporating of the solvent that generate the organic semiconductor films on the substrate. The patterned bottom-contact transistor arrays exhibit carrier mobility of 2.0 × 10⁻³ cm² V⁻¹ s⁻¹, while no field-effect characteristics can be detected for bottom-contact arrays without hydrophobic treatment. Such reliable, fast and solution-based patterned OFET arrays are highly desirable for large-scale and low-cost production.     

Direct UV Patterning of Electronically Active Fullerene Films

We utilize UV light for the attainment of high‐resolution, electronically active patterns in [6,6]‐phenyl C₆₁‐butyric acid methyl ester (PCBM) films. The patterns are created by directly exposing selected parts of a solution‐cast PCBM film to UV light, and thereafter developing the film by immersing it in a tuned developer solution. We demonstrate that it is possible to attain complex, large‐area PCBM structures with a smallest demonstrated‐feature size of 1 μm by this method, and that the patterned PCBM material exhibits a high average electron mobility (1.2 × 10^?2 cm² V^?1 s^?1) in transistor experiments. The employment of UV light for direct patterning of PCBM for electronic applications is attractive, because PCBM exhibits high absorption in the UV range, and no sacrificial photoresist is needed. The patterning is achieved through the transformation by UV light of the soluble PCBM monomers into insoluble dimers with retained attractive electronic properties.     

Exploring the ultrasonic nozzle spray-coating technique for the fabrication of solution-processed organic electronics

The ultrasonic nozzle (US) spray method was investigated for its utility in fabricating organic electrodes composed of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a standard conductive polymer material used to produce large-area low-cost OFETs. The US spray technique involves generating a solution spray by first passing the solution through a head and nozzle subjected to ultrasonic vibrations that induce atomization. This method is advantageous in that the resulting spray comprises extremely small solution droplets a few micrometers in diameter, unlike the spray produced using conventional air spray methods. The PEDOT:PSS US solution spraying process was optimized by controlling the flow rate of the N₂ carrier gas and the substrate temperature while monitoring the quality of the resulting PEDOT:PSS electrode films. The pentacene field-effect transistors prepared using the US spray method displayed a maximum field-effect mobility of 0.47 cm²V⁻¹s⁻¹ (with an average value of 0.31 cm²V⁻¹s⁻¹), 35% better than the mobilities achieved using the conventional air spray method. In addition, the device-to-device reproducibility was improved, as indicated by a decrease in the standard deviation of the mobility values from 30% for the air spray devices to 24% for the US spray devices. These results indicated that the US spray technique is efficient and superior to the conventional air spray method for the development of low-cost large-area organic electronics.     

High‐Performance Organic Photovoltaic Devices Using a New Amorphous Molecular Material with High Hole Drift Mobility,Tris[4‐(5‐phenylthiophen‐2‐yl)phenyl]amine

A new amorphous molecular material, tris[4‐(5‐phenylthiophen‐2‐yl)phenyl]amine (TPTPA), is synthesized and characterized. TPTPA forms a stable amorphous glass with a glass‐transition temperature of 83 °C when the melt sample is cooled. It also forms amorphous thin films by a thermal deposition technique. TPTPA exhibits a hole drift mobility of 1.0 × 10^?2 cm² V^?1 s^?1 at an electric field of 1.0 × 10⁵ V cm^?1 and at 293 K, as determined by the time‐of‐flight method, which is of the highest level among those of amorphous molecular materials. pn‐Heterojunction organic photovoltaic devices (OPVs) using TPTPA as an electron donor and C₆₀ or C₇₀ as an electron acceptor exhibit high performance with fill factors of 0.66～0.71 and power conversion efficiencies of 1.7～2.2% under air‐mass (AM) 1.5G illumination at an intensity of 100 mW cm^?2, which are of the highest level ever reported for OPVs using amorphous molecular materials.