The effect of residual palladium on the performance of organic electrochemical transistors

Open-flask, ambient temperature direct arylation synthesis of mixed ionic-electronic conductors

Conjugated polymers are widely studied for application areas ranging from energy technology to wearable electronics and bioelectronics. To develop a truly sustainable technology, environmentally benign synthesis is essential. Here, the open-flask synthesis of a multitude of conjugated polymers at room temperature by ambient direct arylation polymerization (ADAP) is demonstrated. The batch synthesis of over 100 grams of polymer in a green solvent and continuous droplet flow synthesis without any solid support is described. Polymers prepared by ADAP are characterized by improved structural order compared to materials prepared by other methods. Hence, organic electrochemical transistors (OECTs) feature beyond state-of-the-art electrical properties, i.e., an OECT hole mobility μ as high as 6 cm2 V-1 s-1, a volumetric capacitance C* over 200 F cm-3, and thus a figure of merit [μC*] exceeding 1100 F cm-1 V-1 s-1. Thus, ADAP paves the way for the benign and large-scale production of high-performance conjugated polymers.

In Situ Electropolymerized Ambipolar Copolymers for Vertical OECTs

A novel approach is reported for obtaining ambipolar electroactive polymers via in situ electropolymerization for vertical organic electrochemical transistor (vOECT) applications. It is shown that electropolymerization is a practical and efficient method to obtain copolymers without contamination from chemical polymerization processes. To this end, two monomers, G-DTP-Bu-NDI and G-DTP-G-NDI, are proposed, comprising naphthalene diimide (NDI) as the acceptor core and dithienopyrrole (DTP) as the donor unit, capable of forming carbon-carbon bonds under the influence of an electric current. The incorporation of oligo(oxyethylene) (OEG) side groups ensures their amphiphilicity. Both compounds underwent successful electrochemical polymerization, resulting in thin, porous, uniform polymer layers on the electrode surface. The synthesized polymers are further examined using electrochemical and spectroelectrochemical techniques in both organic and aqueous electrolytes. Regardless of the electrolyte medium (aqueous or non-aqueous), poly(G-DTP-Bu-NDI), and poly(G-DTP-G-NDI) exhibit stable electroactivity, as demonstrated by numerous scans showing ambipolar redox behavior. Both polymers are tested as components of vertical OECTs, following in situ electrochemical deposition within a 350 nm channel. The recorded transfer characteristics suggest that the fabricated donor-acceptor (D-A) compounds hold promise for developing a new generation of ambipolar ECT devices.

π-Conjugated Polymers for High-Performance Organic Electrochemical Transistors: Molecular Design Strategies, Applications and Perspectives

The last decade has witnessed significant progress in organic electrochemical transistors (OECTs) due to their enormous potential applications in various bioelectronic devices, such as artificial synapses, biological interfaces, and biosensors. The remarkable advance in this field is highly powered by the development of novel organic mixed ionic/electronic conductors (OMIECs). π-Conjugated polymers (CPs), which are widely used in various optoelectronics, are emerging as key channel materials for OECTs. In this review, after briefly introducing OECT, we then mainly focus on the latest progress in CPs for high-performance OECTs. The correlations of their structure, basic physicochemical properties, and device performance are elucidated by evaluating their electronic characters, optoelectronic properties, and OECT performance. Then, the applications of CP-based OECTs are briefly presented. Finally, we discuss several remaining issues or challenges in this field and give our insights into advancing CPs for enhanced OECT performance.

The Influence of Alkyl Spacers and Molecular Weight on the Charge Transport and Storage Properties of Oxy-Bithiophene-Based Conjugated Polymers

Conjugated polymers (CPs) with polar side chains can conduct electronic and ionic charges simultaneously, making them promising for bioelectronics, electrocatalysis and energy storage. Recent work showed that adding alkyl spacers between CP backbones and polar side chains improved electronic charge carrier mobility, reduced swelling and enhanced stability, without compromising ion transport. However, how alkyl spacers impact polymer backbone conformation and, subsequently, electronic properties remain unclear. In this work, we design two oxy-bithiophene-based CP series, each featuring progressively extended alkyl spacer lengths and two distinct molecular weight (MW) distributions. Using operando characterisations, we evaluate the (spectro)electrochemical and swelling properties of the polymer thin films, and their performance in organic field-effect transistors and organic electrochemical transistors. Surprisingly, alkyl spacers negatively impact the hole mobility of our polymers, with higher MW amplifying this effect. Using molecular dynamics simulations, we show that it is thermodynamically favourable for adjacent non-polar alkyl spacers to aggregate in polar electrolytes, leading to backbone twisting. Further spectroscopic measurements corroborate this prediction. Our findings demonstrate the active interactions between side chain structure, MW and electrolyte/solvent polarity in influencing polymer performance, underscoring the importance of considering solvation environment effects on polymer conformation when designing new mixed conducting CPs for electrochemical applications.

Trace Dual-Crosslinkable Additives Enable Direct Microlithography for Enhanced Organic Electrochemical Transistors

Similar to silicon-based electronics, the implementation of micro/nano-patterning to facilitate complex device architectures and high-density integration is crucial to the development of organic electronics. Among various patterning techniques, direct microlithography (DML) is highly applicable and extensively adopted in organic electronics, such as organic electrochemical transistors (OECTs). However, conventional DML often requires high crosslinker concentrations, leading to compromised electrical performance. To address this challenge, a novel strategy is developed that combines supramolecular and covalent interactions by incorporating a polyrotaxane supramolecular crosslinker (PR) into poly(benzodifurandione) (PBFDO). The PR forms a hydrogen bonding network with PBFDO and undergoes UV-triggered covalent crosslinking among its molecules, providing solvent resistance even at trace loading levels (<0.1 wt%). This approach enables precise patterning of PBFDO with feature sizes below 1 µm while preserving high electrical performance. Notably, PR also serves as a performance enhancer, promoting molecular ordering and ionic conduction within PBFDO. OECTs fabricated with PR-crosslinked PBFDO exhibit about one-order-of-magnitude increase in ON/OFF ratio, a 42% increase in µC* (reaching 2460 F cm-1 V-1 s-1), and elevated operational stability compared to pristine ones. This multifunctional crosslinker offers a scalable solution for high-performance, high-density organic electronics and opens new avenues for supramolecular chemistry applications in this field.

Anisole Processible n-Type Conjugated Polymers Synthesized via C─H/C─H Oxidative Direct Arylation Polycondensation for Organic Electrochemical Transistors

The development of n-type polymers for organic electrochemical transistors (OECTs) has lagged significantly behind their p-type counterparts. Moreover, these polymers are often synthesized via Stille polycondensation. Herein, three polymers with thiazole-flanked diketopyrrolopyrrole is synthesized as the monomer through C─H/C─H oxidative direct arylation polycondensation (Oxi-DArP). This protocol employs unfunctionalized (C─H terminated) monomers, and the generated byproducts are environmentally benign. The electron-deficient polymer backbone confers these polymers with LUMO energy levels below -4.20 eV, enabling all of them to exhibit n-type behavior in OECTs. Additionally, the resulting polymers are soluble in the green solvent anisole. With an optimized alkyl spacer between oligo(ethylene glycol) side chain and conjugated backbone, the polymer gTzDPP-C8 showed the best device performance with geometry normalized transconductance (gm,norm) up to 6.31 S cm-1 and µC* up to 23.1 F V-1 cm-1 s-1. This work has successfully proved that C─H/C─H Oxi-DArP is a promising method for synthesizing n-type OMIECs to fulfill high-performance OECTs.

High Performance Organic Mixed Ionic-Electronic Polymeric Conductor with Stability to Autoclave Sterilization

We present a series of newly developed donor-acceptor (D-A) polymers designed specifically for organic electrochemical transistors (OECTs) synthesized by a straightforward route. All polymers exhibited accumulation mode behavior in OECT devices, and tuning of the donor comonomer resulted in a three-order-of-magnitude increase in transconductance. The best polymer gFBT-g2T, exhibited normalized peak transconductance (gm,norm) of 298±10.4 S cm-1 with a corresponding product of charge-carrier mobility and volumetric capacitance, μC*, of 847 F V-1 cm-1 s-1 and a μ of 5.76 cm2 V-1 s-1, amongst the highest reported to date. Furthermore, gFBT-g2T exhibited exceptional temperature stability, maintaining the outstanding electrochemical performance even after undergoing a standard (autoclave) high pressure steam sterilization procedure. Steam treatment was also found to promote film porosity, with the formation of circular 200-400 nm voids. These results demonstrate the potential of gFBT-g2T in p-type accumulation mode OECTs, and pave the way for the use in implantable bioelectronics for medical applications.

Dual-Modal Memory Enabled by a Single Vertical N-Type Organic Artificial Synapse for Neuromorphic Computing

Complementary neural network circuits combining multifunctional high-performance p-type with n-type organic artificial synapses satisfy sophisticated applications such as image cognition and prosthesis control. However, implementing the dual-modal memory features that are both volatile and nonvolatile in a synaptic transistor is challenging. Herein, for the first time, we propose a single vertical n-type organic synaptic transistor (VNOST) with a novel polymeric organic mixed ionic-electronic conductor as the core channel material to achieve dual-modal synaptic learning/memory behaviors at different operating current densities via the formation of an electric double layer and the reversible ion doping. As a volatile synaptic device, the resulting VNOST demonstrated an unprecedented operating current density of MA cm-2. Meanwhile, it is capable of 150 analog states, symmetric conductance modulation, and good state retention (100 s) for a nonvolatile synapse. Importantly, the artificial neural networks (ANNs) for recognition accuracy of the handwritten digital data sets recognition rate up to 94% based on its nonvolatile feature. This study provides a promising platform for building organic neuromorphic network circuits in complex application scenarios where high-performing n-type organic synapse transistors with dual-mode memory characters are necessitated.

Small-Molecule Mixed Ionic-Electronic Conductors for Efficient N-Type Electrochemical Transistors: Structure-Function Correlations

The fundamental challenge in electron-transporting organic mixed ionic-electronic conductors (OMIECs) is simultaneous optimization of electron and ion transport. Beginning from Y6-type/U-shaped non-fullerene solar cell acceptors, we systematically synthesize and characterize molecular structures that address the aforementioned challenge, progressively introducing increasing numbers of oligoethyleneglycol (OEG; g) sidechains from 1 g to 3 g, affording OMIECs 1gY, 2gY, and 3gY, respectively. The crystal structure of 1gY preserves key structural features of the Yn series: a U-shaped/planar core, close π-π molecular stacking, and interlocked acceptor groups. Versus inactive Y6 and Y11, all of the new glycolated compounds exhibit mixed ion-electron transport in both conventional organic electrochemical transistor (cOECT) and vertical OECT (vOECT) architectures. Notably, 3gY with the highest OEG density achieves a high transconductance of 16.5 mS, an on/off current ratio of ~106, and a turn-on/off response time of 94.7/5.7 ms in vOECTs. Systematic optoelectronic, electrochemical, architectural, and crystallographic analysis explains the superior 3gY-based OECT performance in terms of denser ngY OEG content, increased crystallite dimensions with decreased long-range crystalline order, and enhanced film hydrophilicity which facilitates ion transport and efficient redox processes. Finally, we demonstrate an efficient small-molecule-based complementary inverter using 3gY vOECTs, showcasing the bioelectronic applicability of these new small-molecule OMIECs.

On-site biosignal amplification using a single high-spin conjugated polymer

On-site or in-sensor biosignal transduction and amplification can offer several benefits such as improved signal quality, reduced redundant data transmission, and enhanced system integration. Ambipolar organic electrochemical transistors (OECTs) are promising for this purpose due to their high transconductance, low operating voltage, biocompatibility, and suitability for miniaturized amplifier design. However, limitations in material performance and stability have hindered their application in biosignal amplification. Here, we propose using high-spin, hydrophilic conjugated polymers and a computational screening approach to address this challenge. We designed a high-spin polymer, namely P(TII-2FT), which exhibits satisfactory, stable, and balanced ambipolar OECT performance. The figure-of-merits achieved by the P(TII-2FT) devices surpass those of the current leading materials by 5 to 20 times, resulting in remarkable voltage gains while maintaining a compact form factor. Based on this amplifier, we have successfully achieved on-site capture and amplification of various electrophysiological signals with greatly enhanced signal quality.

The Role of Side Chains and Hydration on Mixed Charge Transport in n-Type Polymer Films

Introducing ethylene glycol (EG) side chains to a conjugated polymer backbone is a well-established synthetic strategy for designing organic mixed ion-electron conductors (OMIECs). However, the impact that film swelling has on mixed conduction properties has yet to be scoped, particularly for electron-transporting (n-type) OMIECs. Here, the authors investigate the effect of the length of branched EG chains on mixed charge transport of n-type OMIECs based on a naphthalene-1,4,5,8-tetracarboxylic-diimide-bithiophene backbone. Atomic force microscopy (AFM), grazing-incidence wide-angle X-ray scattering (GIWAXS), and scanning tunneling microscopy (STM) are used to establish the similarities between the common-backbone films in dry conditions. Electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) and in situ GIWAXS measurements reveal stark changes in film swelling properties and microstructure during electrochemical doping, depending on the side chain length. It is found that even in the loss of the crystallite content upon contact with the aqueous electrolyte, the films can effectively transport charges and that it is rather the high water content that harms the electronic interconnectivity within the OMIEC films. These results highlight the importance of controlling water uptake in the films to impede charge transport in n-type electrochemical devices.

High Throughput Characterization of Organic Thin Film Transistors

Automation is vital to accelerating research. In recent years, the application of self-driving labs to materials discovery and device optimization has highlighted many benefits and challenges inherent to these new technologies. Successful automated workflows offer tangible benefits to fundamental science and industrial scale-up by significantly increasing productivity and reproducibility all while enabling entirely new types of experiments. However, it's implemtation is often time-consuming and cost-prohibitive and necessitates establishing multidisciplinary teams that bring together domain-specific knowledge with specific skillsets in computer science and engineering. This perspective article provides a comprehensive overview of how the research group has adopted "hybrid automation" over the last 8 years by using simple automatic electrical testers (autotesters) as a tool to increase productivity and enhance reproducibility in organic thin film transistor (OTFT) research. From wearable and stretchable electronics to next-generation sensors and displays, OTFTs have the potential to be a key technology that will enable new applications from health to aerospace. The combination of materials chemistry, device manufacturing, thin film characterization and electrical engineering makes OTFT research challenging due to the large parameter space created by both diverse material roles and device architectures. Consequently, this research stands to benefit enormously from automation. By leveraging the multidisciplinary team and taking a user-centered design approach in the design and continued improvement of the autotesters, the group has meaningfully increased productivity, explored research avenues impossible with traditional workflows, and developed as scientists and engineers capable of effectively designing and leveraging automation to build the future of their fields to encourage this approach, the files for replicating the infrastructure are included, and questions and potential collaborations are welcomed.

Soft hydrogel semiconductors with augmented biointeractive functions

Hydrogels, known for their mechanical and chemical similarity to biological tissues, are widely used in biotechnologies, whereas semiconductors provide advanced electronic and optoelectronic functionalities such as signal amplification, sensing, and photomodulation. Combining semiconducting properties with hydrogel designs can enhance biointeractive functions and intimacy at biointerfaces, but this is challenging owing to the low hydrophilicity of polymer semiconductors. We developed a solvent affinity-induced assembly method that incorporates water-insoluble polymer semiconductors into double-network hydrogels. These semiconductors exhibited tissue-level moduli as soft as 81 kilopascals, stretchability of 150% strain, and charge-carrier mobility up to 1.4 square centimeters per volt per second. When they are interfaced with biological tissues, their tissue-level modulus enables alleviated immune reactions. The hydrogel's high porosity enhances molecular interactions at semiconductor-biofluid interfaces, resulting in photomodulation with higher response and volumetric biosensing with higher sensitivity.

Molecular Ordering Manipulation in Fused Oligomeric Mixed Conductors for High-Performance n-Type Organic Electrochemical Transistors

Advanced n-type organic electrochemical transistors (OECTs) play an important part in bioelectronics, facilitating the booming of complementary circuits-based biosensors. This necessitates the utilization of both n-type and p-type organic mixed ionic-electronic conductors (OMIECs) exhibiting a balanced performance. However, the observed subpar electron charge transport ability in most n-type OMIECs presents a significant challenge to the overall functionality of the circuits. In response to this issue, we achieve high-performance OMIECs by leveraging a series of fused electron-deficient monodisperse oligomers with mixed alkyl and glycol chains. Through molecular ordering manipulation by optimizing of their alkyl side chains, we attained a record-breaking OECT electron mobility of 0.62 cm2/(V s) and μC* of 63.2 F/(cm V s) for bgTNR-3DT with symmetrical alkyl chains. Notably, the bgTNR-3DT film also exhibits the highest structural ordering, smallest energetic disorder, and the lowest trap density among the series, potentially explaining its ideal charge transport property. Additionally, we demonstrate an organic inverter incorporating bgTNR-3DT OECTs with a gain above 30, showcasing the material's potential for constructing organic circuits. Our findings underscore the indispensable role of alkyl chain optimization in the evolution of prospective high performance OMIECs for constructing advanced organic complementary circuits.

Over 19% Efficient Inverted Organic Photovoltaics Featuring a Molecularly Doped Metal Oxide Electron-Transporting Layer

Molecular doping is commonly utilized to tune the charge transport properties of organic semiconductors. However, applying this technique to electrically dope inorganic materials like metal oxide semiconductors is challenging due to the limited availability of molecules with suitable energy levels and processing characteristics. Herein, n-type doping of zinc oxide (ZnO) films is demonstrated using 1,3-dimethylimidazolium-2-carboxylate (CO2-DMI), a thermally activated organic n-type dopant. Adding CO2-DMI into the ZnO precursor solution and processing it atop a predeposited indium oxide (InOx) layer yield InOx/n-ZnO heterojunctions with increased electron field-effect mobility of 32.6 cm2 V-1 s-1 compared to 18.5 cm2 V-1 s-1 for the pristine InOx/ZnO bilayer. The improved electron transport originates from the ZnO's enhanced crystallinity, reduced hydroxyl concentrations, and fewer oxygen vacancy groups upon doping. Applying the optimally doped InOx/n-ZnO heterojunctions as the electron-transporting layers (ETLs) in organic photovoltaics (OPVs) yields cells with improved power conversion efficiency of 19.06%, up from 18.3% for devices with pristine ZnO, and 18.2% for devices featuring the undoped InOx/ZnO ETL. It is shown that the all-around improved OPV performance originates from synergistic effects associated with CO2-DMI doping of the thermally grown ZnO, highlighting its potential as an electronic dopant for ZnO and potentially other metal oxides.

Tunable anti-ambipolar vertical bilayer organic electrochemical transistor enable neuromorphic retinal pathway

Increasing demand for bio-interfaced human-machine interfaces propels the development of organic neuromorphic electronics with small form factors leveraging both ionic and electronic processes. Ion-based organic electrochemical transistors (OECTs) showing anti-ambipolarity (OFF-ON-OFF states) reduce the complexity and size of bio-realistic Hodgkin-Huxley(HH) spiking circuits and logic circuits. However, limited stable anti-ambipolar organic materials prevent the design of integrated, tunable, and multifunctional neuromorphic and logic-based systems. In this work, a general approach for tuning anti-ambipolar characteristics is presented through assembly of a p-n bilayer in a vertical OECT (vOECT) architecture. The vertical OECT design reduces device footprint, while the bilayer material tuning controls the anti-ambipolarity characteristics, allowing control of the device's on and off threshold voltages, and peak position, while reducing size thereby enabling tunable threshold spiking neurons and logic gates. Combining these components, a mimic of the retinal pathway reproducing the wavelength and light intensity encoding of horizontal cells to spiking retinal ganglion cells is demonstrated. This work enables further incorporation of conformable and adaptive OECT electronics into biointegrated devices featuring sensory coding through parallel processing for diverse artificial intelligence and computing applications.

Transient Response and Ionic Dynamics in Organic Electrochemical Transistors

The rapid development of organic electrochemical transistors (OECTs) has ushered in a new era in organic electronics, distinguishing itself through its application in a variety of domains, from high-speed logic circuits to sensitive biosensors, and neuromorphic devices like artificial synapses and organic electrochemical random-access memories. Despite recent strides in enhancing OECT performance, driven by the demand for superior transient response capabilities, a comprehensive understanding of the complex interplay between charge and ion transport, alongside electron-ion interactions, as well as the optimization strategies, remains elusive. This review aims to bridge this gap by providing a systematic overview on the fundamental working principles of OECT transient responses, emphasizing advancements in device physics and optimization approaches. We review the critical aspect of transient ion dynamics in both volatile and non-volatile applications, as well as the impact of materials, morphology, device structure strategies on optimizing transient responses. This paper not only offers a detailed overview of the current state of the art, but also identifies promising avenues for future research, aiming to drive future performance advancements in diversified applications.

High-mobility organic mixed conductors with a low synthetic complexity index via direct arylation polymerization

Through direct arylation polymerization, a series of mixed ion-electron conducting polymers with a low synthetic complexity index is synthesized. A thieno[3,2-b]thiophene monomer with oligoether side chains is used in direct arylation polymerization together with a wide range of aryl bromides with varying electronic character from electron-donating thiophene to electron-accepting benzothiadiazole. The obtained polymers are less synthetically complex than other mixed ion-electron conducting polymers due to higher yield, fewer synthetic steps and less toxic reagents. Organic electrochemical transistors (OECTs) based on a newly synthesized copolymer comprising thieno[3,2-b]thiophene with oligoether side chains and bithiophene exhibit excellent device performance. A high charge-carrier mobility of up to μ = 1.8 cm2 V-1 s-1 was observed, obtained by dividing the figure of merit [μC*] from OECT measurements by the volumetric capacitance C* from electrochemical impedance spectroscopy, which reached a value of more than 215 F cm-3.

An n-Type Conjugated Polymer with Low Crystallinity for High-Performance Organic Thermoelectrics

Conjugated polymers (CPs) with low crystallinity are promising candidates for application in organic thermoelectrics (OTEs), particularly in flexible devices, because the disordered structures of these CPs can effectively accommodate dopants and ensure robust resistance to bending. However, n-doped CPs usually exhibit poor thermoelectric performance, which hinders the development of high-performance thermoelectric generators. Herein, we report an n-type CP (ThDPP-CNBTz) comprising two acceptor units: a thiophene-flanked diketopyrrolopyrrole and a cyano-functionalized benzothiadiazole. ThDPP-CNBTz shows a low LUMO energy level of below -4.20 eV and features low crystallinity, enabling high doping efficiency. Moreover, the dual-acceptor design enhances polaron delocalization, resulting in good thermoelectric performance. After n-doping, ThDPP-CNBTz exhibits an average electrical conductivity (σ) of 50.6 S cm-1 and a maximum power factor (PF) of 126.8 μW m-1 K-2, which is among the highest values reported for solution-processed n-type CPs to date. Additionally, a solution-processed flexible OTE device based on doped ThDPP-CNBTz exhibits a maximum PF of 70 μW m-1 K-2; the flexible device also shows remarkable resistance to bending strain, with only a marginal change in σ after 600 bending cycles. The findings presented in this work will advance the development of n-type CPs for OTE devices, and flexible devices in particular.

Charge Carrier Induced Structural Ordering And Disordering in Organic Mixed Ionic Electronic Conductors

Operational stability underpins the successful application of organic mixed ionic-electronic conductors (OMIECs) in a wide range of fields, including biosensing, neuromorphic computing, and wearable electronics. In this work, both the operation and stability of a p-type OMIEC material of various molecular weights are investigated. Electrochemical transistor measurements reveal that device operation is very stable for at least 300 charging/discharging cycles independent of molecular weight, provided the charge density is kept below the threshold where strong charge-charge interactions become likely. When electrochemically charged to higher charge densities, an increase in device hysteresis and a decrease in conductivity due to a drop in the hole mobility arising from long-range microstructural disruptions are observed. By employing operando X-ray scattering techniques, two regimes of polaron-induced structural changes are found: 1) polaron-induced structural ordering at low carrier densities, and 2) irreversible structural disordering that disrupts charge transport at high carrier densities, where charge-charge interactions are significant. These operando measurements also reveal that the transfer curve hysteresis at high carrier densities is accompanied by an analogous structural hysteresis, providing a microstructural basis for such instabilities. This work provides a mechanistic understanding of the structural dynamics and material instabilities of OMIEC materials during device operation.

Effects of Processing-Induced Contamination on Organic Electronic Devices

Organic semiconductors are a family of pi-conjugated compounds used in many applications, such as displays, bioelectronics, and thermoelectrics. However, their susceptibility to processing-induced contamination is not well understood. Here, it is shown that many organic electronic devices reported so far may have been unintentionally contaminated, thus affecting their performance, water uptake, and thin film properties. Nuclear magnetic resonance spectroscopy is used to detect and quantify contaminants originating from the glovebox atmosphere and common laboratory consumables used during device fabrication. Importantly, this in-depth understanding of the sources of contamination allows the establishment of clean fabrication protocols, and the fabrication of organic field effect transistors (OFETs) with improved performance and stability. This study highlights the role of unintentional contaminants in organic electronic devices, and demonstrates that certain stringent processing conditions need to be met to avoid scientific misinterpretation, ensure device reproducibility, and facilitate performance stability. The experimental procedures and conditions used herein are typical of those used by many groups in the field of solution-processed organic semiconductors. Therefore, the insights gained into the effects of contamination are likely to be broadly applicable to studies, not just of OFETs, but also of other devices based on these materials.

Efficient N-Type Organic Electrochemical Transistors and Field-Effect Transistors Based on PNDI-Copolymers Bearing Fluorinated Selenophene-Vinylene-Selenophenes

n-Type organic electrochemical transistors (OECTs) and organic field-effect transistors (OFETs) are less developed than their p-type counterparts. Herein, polynaphthalenediimide (PNDI)-based copolymers bearing novel fluorinated selenophene-vinylene-selenophene (FSVS) units as efficient materials for both n-type OECTs and n-type OFETs are reported. The PNDI polymers with oligo(ethylene glycol) (EG7) side chains P(NDIEG7-FSVS), affords a high µC* of > 0.2 F cm-1  V-1  s-1 , outperforming the benchmark n-type Pg4NDI-T2 and Pg4NDI-gT2 by two orders of magnitude. The deep-lying LUMO of -4.63 eV endows P(NDIEG7-FSVS) with an ultra-low threshold voltage of 0.16 V. Moreover, the conjugated polymer with octyldodecyl (OD) side chains P(NDIOD-FSVS) exhibits a surprisingly low energetic disorder with an Urbach energy of 36 meV and an ultra-low activation energy of 39 meV, resulting in high electron mobility of up to 0.32 cm2  V-1  s-1 in n-type OFETs. These results demonstrate the great potential for simultaneously achieving a lower LUMO and a tighter intermolecular packing for the next-generation efficient n-type organic electronics.

Side-Chain Engineering in Hydrophilic n-Type π-Conjugated Polymers for Enhanced Reactivity

Minor changes to side chains in conjugated polymers (CPs) can have pronounced effects on polymer properties by altering backbone planarity, solubility, and interaction with ions. Here, we report the photocontrolled synthesis of hydrophilic CPs from Grignard monomers and find that switching from alkyl to oligo(ethylene glycol) (OEG) side chains changes their photoreactivity. Specifically, installing hydrophilic side chains on the same monomer core yields higher molecular weight polymers and allows polymerization to proceed with lower-energy red light. Additionally, we discover a side chain decomposition pathway for N-OEG monomers, which are prevalent in CP research. Decomposition can be overcome by adding an extra methylene unit in the side chains without compromising polymer molecular weight or hydrophilicity. Importantly, this polymerization does not require transition metal catalysts and is a promising approach to the preparation of n-type conjugated block copolymers.