A Discolorable Flexible Synaptic Transistor for Wearable Health Monitoring

Multifunctional intelligent wearable electronics, providing integrated physiological signal analysis, storage, and display for real-time and on-site health status diagnosis, have great potential to revolutionize health monitoring technologies. Advanced wearable systems combine isolated digital processor, memory, and display modules for function integration; however, they suffer from compatibility and reliability issues. Here, we introduce a flexible multifunctional electrolyte-gated transistor (EGT) that integrates synaptic learning, memory, and autonomous discoloration functionalities for intelligent wearable application. This device exhibits synergistic light absorption coefficient changes during voltage-gated ion doping that modulate the electrical conductance changes for synaptic function implementation. By adaptively changing color, the EGT can differentiate voltage pulse inputs with different frequency, amplitude, and duration parameters, exhibiting excellent reversibility and reliability. We developed a smart wearable monitoring system that incorporates EGT devices and sensors for respiratory and electrocardiogram signal analysis, providing health warnings through real-time and on-site discoloration. This study represents a significant step toward smart wearable technologies for health management, offering health evaluation through intelligent displays.

Semiconducting Polymer Nanoporous Thin Films as a Tool to Regulate Intracellular ROS Balance in Endothelial Cells

The design of soft and nanometer-scale photoelectrodes able to stimulate and promote the intracellular concentration of reactive oxygen species (ROS) is searched for redox medicine applications. In this work, we show semiconducting polymer porous thin films with an enhanced photoelectrochemical generation of ROS in human umbilical vein endothelial cells (HUVECs). To achieve that aim, we synthesized graft copolymers, made of poly(3-hexylthiophene) (P3HT) and degradable poly(lactic acid) (PLA) segments, P3HT-g-PLA. In a second step, the hydrolysis of sacrificial PLA leads to nanometer-scale porous P3HT thin films. The pore sizes in the nm regime (220-1200 nm) were controlled by the copolymer composition and the structural arrangement of the copolymers during the film formation, as determined by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The porous P3HT thin films showed enhanced photofaradaic behavior, generating a higher concentration of ROS in comparison to non-porous P3HT films, as determined by scanning electrochemical microscopy (SECM) measurements. The exogenous ROS production was able to modulate the intracellular ROS concentration in HUVECs at non-toxic levels, thus affecting the physiological functions of cells. Results presented in this work provide an important step forward in the development of new tools for precise, on-demand, and non-invasive modulation of intracellular ROS species and may be potentially extended to many other physiological or pathological cell models.

On the Donor: Acceptor Features for Poly(3-hexylthiophene): TiO2 Quantum Dots Hybrid Materials Obtained via Water Vapor Flow Assisted Sol-Gel Growth

Here, we present a novel methodology for the preparation of P3HT:TiO₂ quantum dots hybrid materials via water vapor flow-assisted sol-gel growth focusing on the structural, optical and electrical property characterization complemented with first-principles calculations as a promising donor-acceptor system for polymer and hybrid solar cells. X-ray diffraction and UV-Vis spectroscopy analyses suggest that the increasing concentration of TiO₂ quantum dots leads to the formation of higher amounts of amorphous regions while the crystalline regions exhibited interesting aspect ratio modifications for the P3HT polymer. Raman spectra evidenced the formation of charge carriers in the P3HT with increasing TiO₂ quantum dots content and the P3HT:TiO₂ 50:50 weight ratio resulted in the best composition for optimizing the bulk electronic conductivity, as evidenced by impedance spectroscopy studies. Our DFT calculations performed for a simplified model of the P3HT:TiO₂ interface revealed that there is an important contribution of the thiophene carbon atoms states in the conduction band at the Fermi level. Finally, our DFT calculations also reveal an evident gain of electron density at the TiO₂ (101) surface while the thiophene rings showed a loss of the electron density, thus confirming that the P3HT:TiO₂ junction acts as a good donor-acceptor system. In our opinion, these results not only present a novel methodology for the preparation of P3HT:TiO₂ quantum dots hybrid materials but also reveal some key aspects to guide the more rational design of polymer and hybrid solar cells.

Core-Shell Architecture in Poly(3-hexylthiophene) Nanoparticles: Tuning of the Photophysical Properties for Enhanced Neuronal Photostimulation

This study shows that entirely thiophene-based core@shell nanoparticles, in which the shell is made of the oxidized form of the core polymer (P3HT@PTDO_x NPs), result in a type II interface at the particle surface. This enables the development of advanced photon nanotransducers with unique chemical-physical and biofunctional properties due to the core@shell nanoarchitecture. We demonstrate that P3HT@PTDO_x NPs present a different spatial localization of the excitation energy with respect to the nonoxidized NPs, showing a prevalence of surface states as a result of a different alignment of the HOMO/LUMO energy levels between the core and shell. This allows for the efficient photostimulation of retinal neurons. Indeed, thanks to the stronger and longer-lived charge separation, P3HT@PTDO_x NPs, administered subretinally in degenerate retinas from the blind Royal College of Surgeons rats, are more effective in photostimulation of inner retinal neurons than the gold standard P3HT NPs.

One-Step Preparation of Semiconductor/Dielectric Bilayer Structures for the Simulation of Flexible Bionic Photonic Synapses

Flexible synaptic devices with information sensing, processing, and storage functions are indispensable in the development of wearable artificial intelligence electronic systems. Here, a semiconductor/dielectric bilayer structure was prepared by a one-step deposition method and used for the first time in a flexible biomimetic photonic synaptic transistor device. Specifically, poly(3-hexylthiophene)-block-poly(phenyl isocyanide) with pentafluorophenyl ester (P3HT-b-PPI(5F)) was prepared as the device active layer, where the P3HT segment served as a carrier transport channel and optical gate and the PPI(5F) segment was used for charge trapping. Various biomimetic synaptic behaviors, such as excitatory postsynaptic currents, paired-pulse facilitation, and short-term/long-term memory, were successfully simulated under green light stimulation. An ultra-low energy consumption of 1.82 fJ was achieved with a greatly reduced operating voltage. Further, the "Morse-code" optical decoding was simulated using the excellent synaptic plasticity of the device. In addition, flexible synaptic devices were prepared by a one-step deposition method and can be well-affixed to arbitrary substrates. This has promising applications in the field of wearable bionic electronics.

Molecular Weight-Dependent Oxidation and Optoelectronic Properties of Defect-Free Macrocyclic Poly(3-hexylthiophene)

The redox behaviors of macrocyclic molecules with an entirely π-conjugated system are of interest due to their unique optical, electronic, and magnetic properties. In this study, defect-free cyclic P3HT with a degree of polymerization (DP_n) from 14 to 43 was synthesized based on our previously established method, and its unique redox behaviors arising from the cyclic topology were investigated. Cyclic voltammetry (CV) showed that the HOMO level of cyclic P3HT decreases from -4.86 eV (14 mer) to -4.89 eV (43 mer), in contrast to the linear counterparts increasing from -4.94 eV (14 mer) to -4.91 eV (43 mer). During the CV measurement, linear P3HT suffered from electro-oxidation at the chain ends, while cyclic P3HT was stable. ESR and UV-Vis-NIR spectroscopy suggested that cyclic P3HT has stronger dicationic properties due to the interactions between the polarons. On the other hand, linear P3HT showed characteristics of polaron pairs with multiple isolated polarons. Moreover, the dicationic properties of cyclic P3HT were more pronounced for the smaller macrocycles.

High-Performance Nitric Oxide Gas Sensors Based on an Ultrathin Nanoporous Poly(3-hexylthiophene) Film

Conjugated polymer (CP)-based organic field-effect transistors (OFETs) have been considered a potential sensor platform for detecting gas molecules because they can amplify sensing signals by controlling the gate voltage. However, these sensors exhibit significantly poorer oxidizing gas sensing performance than their inorganic counterparts. This paper presents a high-performance nitric oxide (NO) OFET sensor consisting of a poly(3-hexylthiophene) (P3HT) film with an ultrathin nanoporous structure. The ultrathin nonporous structure of the P3HT film was created via deposition through the shear-coating-assisted phase separation of polymer blends and selective solvent etching. The ultrathin nonporous structure of the P3HT film enhanced NO gas diffusion, adsorption, and desorption, resulting in the ultrathin nanoporous P3HT-film-based OFET gas sensor exhibiting significantly better sensing performance than pristine P3HT-film-based OFET sensors. Additionally, upon exposure to 10 ppm NO at room temperature, the nanoporous P3HT-film-based OFET gas sensor exhibited significantly better sensing performance (i.e., responsivity ≈ 42%, sensitivity ≈ 4.7% ppm^-1, limit of detection ≈ 0.5 ppm, and response/recovery times ≈ 6.6/8.0 min) than the pristine P3HT-film-based OFET sensors.

Enhanced Nitric Oxide Sensing Performance of Conjugated Polymer Films through Incorporation of Graphitic Carbon Nitride

Organic field-effect transistor (OFET) gas sensors based on conjugated polymer films have recently attracted considerable attention for use in environmental monitoring applications. However, the existing devices are limited by their poor sensing performance for gas analytes. This drawback is attributed to the low charge transport in and the limited charge-analyte interaction of the conjugated polymers. Herein, we demonstrate that the incorporation of graphitic carbon nitride (g-C₃N₄) into the conjugated polymer matrix can improve the sensing performance of OFET gas sensors. Moreover, the effect of graphitic carbon nitride (g-C₃N₄) on the gas sensing properties of OFET sensors based on poly(3-hexylthiophene) (P3HT), a conjugated polymer, was systematically investigated by changing the concentration of the g-C₃N₄ in the P3HT/g-C₃N₄ composite films. The obtained films were applied in OFET to detect NO gas at room temperature. In terms of the results, first, the P3HT/g-C₃N₄ composite films containing 10 wt.% g-C₃N₄ exhibited a maximum charge carrier mobility of ~1.1 × 10^-1 cm² V^-1 S^-1, which was approximately five times higher than that of pristine P3HT films. The fabricated P3HT/g-C₃N₄ composite film based OFET sensors presented significantly enhanced NO gas sensing characteristics compared to those of the bare P3HT sensor. In particular, the sensors based on the P3HT/g-C₃N₄ (90/10) composite films exhibited the best sensing performance relative to that of the bare P3HT sensor when exposed to 10 ppm NO gas: responsivity = 40.6 vs. 18.1%, response time = 129 vs. 142 s, and recovery time = 148 vs. 162 s. These results demonstrate the enormous promise of g-C₃N₄ as a gas sensing material that can be hybridized with conjugated polymers to efficiently detect gas analytes.

Effect of Ultraviolet Activation on Sub-ppm NO2 Sensing Dynamics of Poly(3-hexylthiophene)-Bearing Graft Copolymers

Nitrogen dioxide (NO₂) sensors utilising graft copolymers bearing poly(3-hexylthiophene) chains have been developed and investigated in terms of their operation parameters using different carrier gases (N₂ or air) and in either dark conditions or with ultraviolet (UV) irradiation. Interestingly, sensor performance improved upon transition from N₂ to air, with the inverse being true for most NO₂ sensors. UV irradiation both improved sensor dynamics and stabilised the sensor electrical baseline, allowing sensors based on SilPEG to fulfil the requirements of sensing solutions used in industry (below 10% baseline drift after sensors reach saturation) and making them promising candidates for further development and applications. Based on conducted multi-variate experiments, an initial mechanism underlying the interplay of exposure to oxygen (present in air) and UV irradiation was postulated.

Influence of Asphaltene Modification on Structure of P3HT/Asphaltene Blends: Molecular Dynamics Simulations

Further development and commercialization of bulk heterojunction (BHJ) solar cells require the search for novel low-cost materials. The present study addresses the relations between the asphaltenes' chemical structure and the morphology of the poly(3-hexylthiohene) (P3HT)/asphaltene blends as potential materials for the design of BHJ solar cells. By means of all-atom molecular dynamics simulations, the formation of heterophase morphology is observed for the P3HT-based blends with carboxyl-containing asphaltenes, as well as the aggregation of the asphaltenes into highly ordered stacks. Although the π-π interactions between the polyaromatic cores of the asphaltenes in solutions are sufficient for the molecules to aggregate into ordered stacks, in a blend with a conjugated polymer, additional stabilizing factors are required, such as hydrogen bonding between carboxyl groups. It is found that the asphaltenes' aliphatic side groups may improve significantly the miscibility between the polymer and the asphaltenes, thereby preventing the formation of heterophase morphology. The results also demonstrate that the carboxyl-containing asphaltenes/P3HT ratio should be at least 1:1, as a decrease in concentration of the asphaltenes leads to the folding of the polymer chains, lower ordering in the polymer phase and the destruction of the interpenetrating 3D structure formed by P3HT and the asphaltene phases. Overall, the results of the present study for the first time reveal the aggregation behavior of the asphaltenes of varying chemical structures in P3HT, as well the influence of their presence and concentration on the polymer phase structure and blend morphology, paving the way for future development of BHJ solar cells based on the conjugated polymer/asphaltene blends.

Electrically Switchable Film Structure of Conjugated Polymer Composites

Domains rich in different blend components phase-separate during deposition, creating a film morphology that determines the performance of active layers in organic electronics. However, morphological control either relies on additional fabrication steps or is limited to a small region where an external interaction is applied. Here, we show that different semiconductor-insulator polymer composites can be rapidly dip-coated with the film structure electrically switched between distinct morphologies during deposition guided by the meniscus formed between the stationary barrier and horizontally drawn solid substrate. Reversible and repeatable changes between the morphologies used in devices, e.g., lateral morphologies and stratified layers of semiconductors and insulators, or between phase-inverted droplet-like structures are manifested only for one polarity of the voltage applied across the meniscus as a rectangular pulse. This phenomenon points to a novel mechanism, related to voltage-induced doping and the doping-dependent solubility of the conjugated polymer, equivalent to an increased semiconductor content that controls the composite morphologies. This is effective only for the positively polarized substrate rather than the barrier, as the former entrains the nearby lower part of the coating solution that forms the final composite film. The mechanism, applied to the pristine semiconductor solution, results in an increased semiconductor deposition and 40-times higher film conductance.

Low-Energy-Consumption and Electret-Free Photosynaptic Transistor Utilizing Poly(3-hexylthiophene)-Based Conjugated Block Copolymers

Neuromorphic computation possesses the advantages of self-learning, highly parallel computation, and low energy consumption, and is of great promise to overcome the bottleneck of von Neumann computation. In this work, a series of poly(3-hexylthiophene) (P3HT)-based block copolymers (BCPs) with different coil segments, including polystyrene, poly(2-vinylpyridine) (P2VP), poly(2-vinylnaphthalene), and poly(butyl acrylate), are utilized in photosynaptic transistor to emulate paired-pulse facilitation, spike time/rate-dependent plasticity, short/long-term neuroplasticity, and learning-forgetting-relearning processes. P3HT serves as a carrier transport channel and a photogate, while the insulating coils with electrophilic groups are for charge trapping and preservation. Three main factors are unveiled to govern the properties of these P3HT-based BCPs: i) rigidity of the insulating coil, ii) energy levels between the constituent polymers, and iii) electrophilicity of the insulating coil. Accordingly, P3HT-b-P2VP-based photosynaptic transistor with a sought-after BCP combination demonstrates long-term memory behavior with current contrast up to 10⁵ , short-term memory behavior with high paired-pulse facilitation ratio of 1.38, and an ultralow energy consumption of 0.56 fJ at an operating voltage of -0.0003 V. As far as it is known, this is the first work to utilize conjugated BCPs in an electret-free photosynaptic transistor showing great potential to the artificial intelligence technology.

P3HT-Based Organic Solar Cells with a Photoresponse to 1000 nm Enabled by Narrow Band Gap Nonfullerene Acceptors with High HOMO Levels

Three narrow band gap (NBG) acceptors, namely, TTDTC-0F, TTDTC-2F, and TTDTC-4F, were synthesized by introducing a strong electron-donating unit as the central core. The enhanced intramolecular charge transfer endows the three acceptors with high-lying highest occupied molecular orbitals (HOMOs) of ∼-5.20 eV and ultranarrow band gaps (∼1.25 eV). When blended with poly(3-hexylthiophene) (P3HT), all organic solar cells (OSCs) exhibited a broad photoresponse from 300 to ∼1000 nm. Among them, P3HT:TTDTC-4F-based devices achieved the highest efficiency of 7.81% with a prominent J_sc exceeding 22 mA·cm^-2. This study demonstrates that the conjugated molecules with high HOMOs can also function as acceptor materials for P3HT-based OSCs, which opens a window to increase PCEs of P3HT-based OSCs in the future to the level of the devices based on the current state-of-the-art polymer donor materials.

Interfacial Modulation of Graphene by Polythiophene with Controlled Molecular Weight to Enhance Thermal Conductivity

With a trend of continuing improvement in the development of electronic devices, a problem of serious heat accumulation has emerged which has created the need for more efficient thermal management. Graphene sheets (GNS) have drawn much attention with regard to heat transfer because of their excellent in-plane thermal conductivity; however, the ultrahigh interfacial thermal resistance between graphene lamellae has seriously restricted its practical applications. Herein, we describe heat transfer membranes composed of graphene which have been modified by intrinsic thermally conductive polymers with different molecular weights. The presence of macromolecular surface modifiers not only constructed the graphene heat transfer interface by π-π interactions, but also significantly enhanced the membranes' in-plane thermal conductivity by utilizing their intrinsic heat transfer properties. Such results indicated that the in-plane thermal conductivity of the fabricated membrane exhibits a high in-plane thermal conductivity of 4.17 W m-1 K-1, which, containing the GNS modified with 6000 g/mol (Mn) of poly(3-hexylthiophene) (P3HT), was 26 times higher that of poly (vinylidene fluoride) (PVDF). The P3HT molecular chain with specific molecular weight can form more matching structure π-π interactions, which promotes thermal conductivity. The investigation of different molecular weights has provided a new pathway for designing effective interfacial structures to relieve interface thermal resistance in thermally conductive membranes.

Enabling Conducting Polymer Applications: Methods for Achieving High Molecular Weight in Chemical Oxidative Polymerization in Alkyl- and Ether-Substituted Thiophenes

Polythiophenes (PTs) constitute a diverse array of promising materials for conducting polymer applications. However, many of the synthetic methods to produce PTs have been optimized only for the prototypical alkyl-substituted example poly(3-hexylthiophene) (P3HT). Improvement of these methods beyond P3HT is key to enabling the widespread application of PTs. In this work, P3HT and two ether-substituted PTs poly(2-dodecyl-2H,3H-thieno[3,4-b][1,4]dioxine) (PEDOT-C12) and poly(3,4-bis(hexyloxy)thiophene) (PBHOT) are synthesized by the FeCl₃-initiated oxidative method under different conditions. Polymerization was carried out according to a common literature procedure (“reverse addition”) and a modified method (“standard addition”), which differ by the solvent system and the order of addition of reagents to the reaction mixture. Gel-permeation chromatography (GPC) was performed to determine the impact of the different methods on the molecular weights (M_w) and degree of polymerization (X_w) of the polymers relative to polystyrene standards. The standard addition method produced ether-substituted PTs with higher M_w and X_w than those produced using the reverse addition method for sterically unhindered monomers. For P3HT, the highest M_w and X_w were obtained using the reverse addition method. The results show the oxidation potential of the monomer and solution has the greatest impact on the yield and X_w obtained and should be carefully considered when optimizing the reaction conditions for different monomers.

Achieving over 10 % Efficiency in Poly(3-hexylthiophene)-Based Organic Solar Cells via Solid Additives

The photovoltaic performance of organic solar cells (OSCs) based on poly(3-hexylthiophene) (P3HT) has been steadily improved by developing novel non-fullerene acceptors (NFAs) in recent years. Herein, to further improve the performance of P3HT-based OSCs, a solid additive (SA4) and a typical solvent additive [1,8-diiodooctane (DIO)] were employed to process P3HT:ZY-4Cl-based OSCs, respectively. In comparison with the DIO-processed device, the SA4-processed one exhibited a more ordered molecular packing and more favorable phase separation, leading to enhanced charge transport and reduced carrier recombination. As a result, the SA4-processed device delivered a power conversion efficiency (PCE) of 10.24 %, which was much higher than that of the DIO-processed counterpart (6.26 %). This work reported a PCE over 10 % in P3HT-based OSCs for the first time, indicating the promising development of P3HT-based OSCs by morphological modulation.

Electrochemically Synthesized Poly(3-hexylthiophene) Nanowires as Photosensitive Neuronal Interfaces

Poly(3-hexylthiophene) (P3HT) is a hole-conducting polymer that has been intensively used to develop organic optoelectronic devices (e.g., organic solar cells). Recently, P3HT films and nanoparticles have also been used to restore the photosensitivity of retinal neurons. The template-assisted electrochemical synthesis of polymer nanowires advantageously combines polymerization and polymer nanostructuring into one, relatively simple, procedure. However, obtaining P3HT nanowires through this procedure was rarely investigated. Therefore, this study aimed to investigate the template-assisted electrochemical synthesis of P3HT nanowires doped with tetrabutylammonium hexafluorophosphate (TBAHFP) and their biocompatibility with primary neurons. We show that template-assisted electrochemical synthesis can relatively easily turn 3-hexylthiophene (3HT) into longer (e.g., 17 ± 3 µm) or shorter (e.g., 1.5 ± 0.4 µm) P3HT nanowires with an average diameter of 196 ± 55 nm (determined by the used template). The nanowires produce measurable photocurrents following illumination. Finally, we show that primary cortical neurons can be grown onto P3HT nanowires drop-casted on a glass substrate without relevant changes in their viability and electrophysiological properties, indicating that P3HT nanowires obtained by template-assisted electrochemical synthesis represent a promising neuronal interface for photostimulation.

Pyridine End-Capped Polymer to Stabilize Organic Nanoparticle Dispersions for Solar Cell Fabrication through Reversible Pyridinium Salt Formation

Bulk-heterojunction nanoparticle dispersions in water or alcohol can be employed as eco-friendly inks for the fabrication of organic solar cells by printing or coating. However, one major drawback is the need for stabilizing surfactants, which facilitate nanoparticle formation but later hamper device performance. When surfactant-free dispersions are formulated, a strong limitation is imposed by the dispersion concentration due to the tendency of nanoparticles to aggregate. In this work, pyridine end-capped poly(3-hexylthiophene) (P3HT-Py) is synthesized and included as an additive for the stabilization of P3HT:indene-C₆₀ bis-adduct (ICBA) nanoparticle dispersions. In the presence of acetic acid (AcOH), a surface-active pyridinium acetate end-capped P3HT ion pair, P3HT-PyH⁺AcO^-, is formed which effectively stabilizes the dispersion and hence allows the formation of dispersions with smaller nanoparticle sizes and higher concentrations of up to 30 mg/mL in methanol. The dispersions exhibit an enhanced shelf-lifetime of at least 60 days at room temperature. After the deposition of light-harvesting layers from the nanoparticle dispersions, the ion-pair formation is reversed at elevated temperatures leading to regeneration of P3HT-Py and AcOH. The AcOH evaporates from the active layer, while the performance of the corresponding solar cells is not affected by the residual P3HT-Py in the devices. Enhanced nanoparticle stability is achieved with only 0.017 wt % pyridine in the P3HT/ICBA formulation.

Strain-Microstructure-Optoelectronic Inter-Relationship toward Engineering Mechano-Optoelectronic Conjugated Polymer Thin Films

Mechano-optoelectronic (MO) behavior indicates changes in optoelectronic properties in response to the applied mechanical deformation. The MO behavior can be employed to monitor the mechanical deformation of a targeted system by tracing its optoelectronic properties. Poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester (P3HT/PCBM) blend thin films exhibited changes in direct current under tensile strain. Although optoelectronic properties and photovoltaic performance of P3HT/PCBM blends have been studied extensively and intensively, research required for MO properties has a fundamental difference from previous research mostly for solar cells. In research for MO systems, a greater extent of changes in optoelectronic properties under mechanical deformation is favorable. Herein, previous research for optoelectronic properties and mechanical properties of conjugated polymers will be reviewed from a perspective on MO properties. The microstructure of a conjugated polymer thin film plays a pivotal role in its optoelectronic properties and mechanical properties. Key parameters involved in the microstructure of conjugated polymer thin films will be addressed. A scalable process is required to broaden applications of MO systems. Potential challenges in the fabrication of MO conjugated polymer thin films will be discussed. Finally, this review is envisioned to provide insight into the design and manufacturing of MO conjugated polymer thin films.

Solution-Processed Donor-Acceptor Poly(3-hexylthiophene):Phenyl-C61-butyric Acid Methyl Ester Diodes for Low-Voltage α Particle Detection

Diodes fabricated using a blend of poly(3-hexylthiophene) and phenyl-C₆₁-butyric acid methyl ester (6-80 μm thick) as an organic semiconductor component achieved consistent 4 MeV α particle detection. Current-voltage characteristics and current-time measurements were obtained under α irradiation and in its absence. Steady-state and transient (time-of-flight) photoconduction measurements were additionally performed. Low-bias (<20 V) α particle detection gain-efficiency products of order 10^-2 were measured. The α particle detection was achieved reproducibly, reversibly, and repeatably in different devices of varying organic semiconductor layer thicknesses using both the steady-state and time-dependent (dynamic) diode responses. Conductive gain, due to trapped electrons, increased the α particle gain-efficiency product in both forward and reverse bias conditions as well as increasing steady-state photoconduction. The device thickness was optimized to maximize the gain-efficiency product by matching the penetration depth of the α particle, obtained by modeling, to the organic semiconductor layer thickness. Very high confidence α particle detection was achieved (with signal-to-noise ratios exceeding 20) under optimized device dimensions and drive conditions. Hecht function fitting of the gain-efficiency product versus electric field data returns mobility-lifetime products of order 10^-6-10^-7 cm² V^-1. This work demonstrates that solution-processed organic semiconductor diodes are viable for low-voltage α particle detection.

Giga-Gain at Room Temperature in Functionalized Carbon Nanotube Phototransistors Based on a Nonequilibrium Mechanism

Achieving high gain in a photodetector is critical to detect weak light fields because of the need to amplify the signal. Here, we report the observation of a gain exceeding 10⁹ for a phototransistor composed of an array of aligned semiconducting carbon nanotubes functionalized with a nanoscale layer of poly(3-hexylthiophene-2,5-diyl) (P3HT). In contrast to the expectation based on simple band alignments, the phototransistor operates by transferring holes between the P3HT and the CNT, trapping negative charge near the nanotubes. This mechanism leads to an integrating detector that is shown to detect as little as 490 aW and to resolve as few as 8-13 photons/nanotube at room temperature. A detailed experimental and theoretical investigation of the mechanism shows that the phototransistor is most sensitive when prepared in a nonequilibrium state.

Effects of Solvent Vapor Annealing on Morphology and Charge Transport of Poly(3-hexylthiophene) (P3HT) Films Incorporated with Preformed P3HT Nanowires

We systematically studied the influence of solvent vapor annealing on the molecular ordering, morphologies, and charge transport properties of poly(3-hexylthiophene) (P3HT) thin films embedded with preformed crystalline P3HT nanowires (NWs). Solvent vapor annealing (SVA) with chloroform (CF) was found to profoundly impact on the structural and morphological changes, and thus on the charge transport characteristics, of the P3HT-NW-embedded P3HT films. With increased annealing time, the density of crystalline P3HT NWs was increased within the resultant films, and also intra- and intermolecular interactions of the corresponding films were significantly improved. As a result, the P3HT-NW-embedded P3HT films annealed with CF vapor for 20 min resulted in a maximized charge carrier mobility of ~0.102 cm² V⁻¹ s⁻¹, which is higher than that of pristine P3HT films by 4.4-fold (μ = ~0.023 cm² V⁻¹ s⁻¹).

Can Ferroelectricity Improve Organic Solar Cells?

Blends of semiconducting (SC) and ferroelectric (FE) polymers have been proposed for applications in resistive memories and organic photovoltaics (OPV). For OPV, the rationale is that the local electric field associated with the dipoles in a blend could aid exciton dissociation, thus improving power conversion efficiency. However, FE polymers either require solvents or processing steps that are incompatible with those required for SC polymers. To overcome this limitation, SC (poly(3-hexylthiophene)) and FE (poly(vinylidene fluoride-trifluoroethylene)) components are incorporated into a block copolymer and thus a path to a facile fabrication of smooth thin films from suitably chosen solvents is achieved. In this work, the photophysical properties and device performance of organic solar cells containing the aforementioned block copolymer consisting of poly(vinylidene fluoride-trifluoroethylene): P(VDF-TrFE), poly(3-hexylthiophene): P3HT and the electron acceptor phenyl-C₆₁ -butyric acid methyl ester: [60]PCBM are explored. A decrease in photovoltaic performance is observed in blends of the copolymer with P3HT:[60]PCBM, which is attributed to a less favorable nanomorphology upon addition of the copolymer. The role of lithium fluoride (the cathode modification layer) is also clarified in devices containing the copolymer, and it is demonstrated that ferroelectric compensation prevents the ferroelectricity of the copolymer from improving photovoltaic performance in SC-FE blends.

Doped Poly(3-hexylthiophene) Coatings onto Chitosan: A Novel Approach for Developing a Bio-Based Flexible Electronic

Conductive and flexible bio-based materials consisting of chitosan films coated with conductive poly(3-hexylthiophene) (P3HT) were prepared. Thermal, optical, mechanical, morphological, wettability, and conductive properties were analyzed. In a very simple and effective method of chitosan film modification, a controlled volume of a P3HT solution was deposited onto a previously formed chitosan film, assisted by the spin coating method. Later, P3HT-coated chitosan films were doped by simple contact with an aqueous solution of HAuCl₄. The use of HAuCl₄ becomes attractive because the reports on the doping process in this type of material using this reagent are still scarce and recent to date. In addition, since this acid is a well-known metal nanoparticle precursor, its use opens new future perspectives for these materials into new applications. The effect of P3HT concentration and doping times on film properties was studied. Attenuated total reflectance spectroscopy and UV-Vis spectroscopy allowed us to demonstrate that the presence of the P3HT coating and its doping induce significant changes in the vibrational modes and optoelectronic properties of samples. Additionally, the images obtained by scanning electron microscopy showed a well-distributed and homogeneous coating on the surface of chitosan films. Measured conductivity values of doped film samples fall in the range from 821.3 to 2017.4 S/m, representing, to the best of our knowledge, the highest values reported in the literature for chitosan/chitin-based materials. Indeed, these values are around or even higher than those obtained for some materials purely consisting of conductive polymers.

Selective Ammonia-Sensing Platforms Based on a Solution-Processed Film of Poly(3-Hexylthiophene) and p-Doping Tris(Pentafluorophenyl)Borane

Here, we fabricate ammonia sensors based on organic transistors by using poly(3-hexylthiophene) (P3HT) blended with tris(pentafluorophenyl)borane (TPFB) as an active layer. As TPFB is an efficient p-type dopant for P3HT, the current level of the blend films can be easily modulated by controlling the blend ratio. The devices exhibit significantly increased on-state and off-state current levels owing to the ohmic current originated from the large number of charge carriers when the active polymer layer contains TPFB with concentrations up to 20 wt % (P3HT:TPFB = 8:2). The current is decreased at 40 wt % of TPFB (P3HT:TPFB = 6:4). The P3HT:TPFB blend with a weight ratio of 9:1 exhibits the highest sensing performances for various concentrations of ammonia. The device exhibits an increased percentage current response compared to that of a pristine P3HT device. The current response of the P3HT:TPFB (9:1) device at 100 ppm of ammonia is as high as 65.8%, 3.2 times that of the pristine P3HT (20.3%). Furthermore, the sensor based on the blend exhibits a remarkable selectivity to ammonia with respect to acetone, methanol, and dichloromethane, owing to the strong interaction between the Lewis acid (TPFB) and Lewis base (ammonia).

P3HT-Based Polymer Solar Cells with 8.25% Efficiency Enabled by a Matched Molecular Acceptor and Smart Green-Solvent Processing Technology

A novel molecular acceptor of TrBTIC (2,7,12-tris((2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile-7-benzothiadiazole-2-)truxene) is designed by attaching the 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile-benzothiadiazole (BTIC) electron-deficient unit to an electron-rich truxene core. TrBTIC has excellent solubility in common solvents and features good energy level matching with poly(3-hexylthiophene) (P3HT). Interestingly, P3HT can be readily dissolved in warm 1,2,4-trimethylbenzene (TMB), a green solvent, but crystallizes slowly with long-term aging in TMB at room temperature. A prephase separation can thus occur before active blend film deposition, and the separation degree can be easily controlled by varying the aging time. After 40 min of aging, the resulting active blend has the most appropriate phase separation with uniform nanowires, which forms favorable interpenetrating networks for exciton dissociation and charge transport. As a result, the device performance is improved from 6.62% to 8.25%. Excitingly, 8.25% is a new record for P3HT-based solar cells. The study not only provides an efficient nonfullerene acceptor for matching P3HT donors but also develops a promising processing technology to realize high-performance P3HT-based polymer solar cells with an efficiency over 8%.

Nanoscale Visualization and Multiscale Electrochemical Analysis of Conductive Polymer Electrodes

Conductive polymers are exceptionally promising for modular electrochemical applications including chemical sensors, bioelectronics, redox-flow batteries, and photoelectrochemical systems due to considerable synthetic tunability and ease of processing. Despite well-established structural heterogeneity in these systems, conventional macroscopic electroanalytical methods-specifically cyclic voltammetry-are typically used as the primary tool for structure-property elucidation. This work presents an alternative correlative multimicroscopy strategy. Data from laboratory and synchrotron-based microspectroscopies, including conducting-atomic force microscopy and synchrotron nanoscale infrared spectroscopy, are combined with potentiodynamic movies of electrochemical fluxes from scanning electrochemical cell microscopy (SECCM) to reveal the relationship between electrode structure and activity. A model conductive polymer electrode system of tailored heterogeneity is investigated, consisting of phase-segregated domains of poly(3-hexylthiophene) (P3HT) surrounded by contiguous regions of insulating poly(methyl methacrylate) (PMMA), representing an ultramicroelectrode array. Isolated domains of P3HT are shown to retain bulk-like chemical and electronic structure when blended with PMMA and possess approximately equivalent electron-transfer rate constants compared to pure P3HT electrodes. The nanoscale electrochemical data are used to model and predict multiscale electrochemical behavior, revealing that macroscopic cyclic voltammograms should be much more kinetically facile than observed experimentally. This indicates that parasitic resistances rather than redox kinetics play a dominant role in macroscopic measurements in these conductive polymer systems. SECCM further demonstrates that the ambient degradation of the P3HT electroactivity within P3HT/PMMA blends is spatially heterogeneous. This work serves as a roadmap for benchmarking the quality of conductive polymer films as electrodes, emphasizing the importance of nanoscale electrochemical measurements in understanding macroscopic properties.

P3HT Nanofibrils Thin-Film Transistors by Adsorbing Deposition in Suspension

A novel film preparation method utilizing polymer suspension, entitled adsorbing deposition in suspensions (ADS), has been proposed. The poly(3-hexylthiophene) (P3HT) toluene solution forms P3HT nanofibrils dispersed suspension by aging. P3HT nanofibrils are highly crystallized with sharp vibronic absorption spectra. By the ADS method, only P3HT nanofibrils in suspension can be deposited on the substrate surface without any disordered fraction from the dissolved P3HT in suspension. Formed ADS film contains only the nanostructured conjugated polymer. Fabricated polymer thin-film transistor (TFT) utilizing ADS P3HT film shows good TFT performances with low off current, narrow subthreshold swing and large on/off current ratio.

A Quarterthiophene-Based Dye as an Efficient Interface Modifier for Hybrid Titanium Dioxide/Poly(3-hexylthiophene)(P3HT) Solar Cells

This work focused on studying the influence of dyes, including a thiophene derivative dye with a cyanoacrylic acid group ((E)-2-cyano-3-(3′,3′′,3′′′-trihexyl-[2,2′:5′,2′′:5′′,2′′′- quaterthiophene]-5-yl) acrylicacid)(4T), on the photovoltaic performance of titanium dioxide (TiO₂)/poly(3-hexyl thiophene)(P3HT) solar cells. The insertion of dye at the interface improved the efficiency regardless of the dye used. However, 4T dye significantly improved the efficiency by a factor of three when compared to the corresponding control. This improvement is mainly due to an increase in short circuit current density (J_SC), which is consistent with higher hole-mobility reported in TiO₂/P3HT nanocomposite with 4T dye. Optical absorption data further revealed that 4T extended the spectral response of the TiO₂/P3HT nanocomposite, which could also enhance the J_SC. The reduced dark current upon dye insertion ensured the carrier recombination was controlled at the interface. This, in turn, increased the open circuit voltage. An optimized hybrid TiO₂/P3HT device with 4T dye as an interface modifier showed an average efficiency of over 2% under-simulated irradiation of 100 mWcm⁻² (1 sun) with an Air Mass 1.5 filter.

Energetic disorder in perovskite/polymer solar cells and its relationship with the interfacial carrier losses

Previous reports have observed a direct relationship between the polymer poly(3-hexylthiophene) molecular weight (MW) and the perovskite solar cell (PSC) efficiency. Herein, we analyse how the differences in MW and the differences in energetic disorder influence the interfacial carrier losses in the PSCs under operation conditions and explain the observed differences. This article is part of a discussion meeting issue 'Energy materials for a low carbon future'.

The Different Outcomes of Electrochemical Copolymerisation: 3-Hexylthiophene with Indole, Carbazole or Fluorene

Electrochemical polymerisation is reported to be a method for readily producing copolymers of various conjugated molecules. We employed this method for mixtures of indole, carbazole or fluorene with 3-hexylthiophene (HT), in order to obtain their soluble copolymers. Although polymer films were obtained, infrared (IR) and Raman investigations showed that instead of the expected linear copolymers, polyindole and polycarbazole N-substituted with HT, as well as a poly(3-hexylthiophene) (PHT)/polyfluorene blend were produced instead. Boron trifluoride diethyl etherate was also used in an attempt to promote copolymerisation, but the produced deposits were found to be highly degraded.

Controlled Self-Assembly of Conjugated Polymers via a Solvent Vapor Pre-Treatment for Use in Organic Field-Effect Transistors

A facile solution-processing strategy toward well-ordered one-dimensional nanostructures of conjugated polymers via a non-solvent vapor treatment was demonstrated, which resulted in enhancements to the charge transport characteristics of the polymers. The amount of crystalline poly(3-hexylthiophene) (P3HT) nanofibers was precisely controlled by simply varying the exposure time of solutions of P3HT solutions to non-solvent vapor. The effects of non-solvent vapor exposure on the molecular ordering and morphologies of the resultant P3HT films were systematically investigated using ultraviolet-visible (UV-vis) spectroscopy, polarized optical microscopy (POM), grazing incidence X-ray diffraction (GIXRD), and atomic force microscopy (AFM). The non-solvent vapor facilitates the π–π stacking in P3HT to minimize unfavorable interactions between the poor solvent molecules and P3HT chains. P3HT films deposited from the non-solvent vapor-treated P3HT solutions exhibited an approximately 5.6-fold improvement in charge carrier mobility as compared to that of pristine P3HT films (7.8 × 10⁻² cm² V⁻¹ s⁻¹ vs. 1.4 × 10⁻² cm² V⁻¹ s⁻¹). The robust and facile strategy presented herein would be applicable in various opto-electronics applications requiring precise control of the molecular assembly, such as organic photovoltaic cells, field-effect transistors, light-emitting diodes, and sensors.

Poly(3-hexylthiophene) Grafting and Molecular Dilution: Study of a Class of Conjugated Graft Copolymers

A type of graft copolymer based on polysiloxane and regioregular poly(3-hexylthiophene) (P3HT) has been synthesised and its properties have been studied alongside those of its parent conjugated polymer-regioregular P3HT. Electrochemical analysis has revealed more significant changes in conformation of the copolymer film than was observed for P3HT. UV-Vis-NIR spectroelectrochemical investigation provided evidence of improved doping reversibility of the copolymer, despite its marginally increased band gap, as also confirmed by electroconductometric analysis. Evidence has been shown, indicating that polaron mobilities in both P3HT and the copolymer are higher than those of bipolaronic charge carriers, even though both systems exhibit standard doping/dedoping patterns. The grafted copolymer was tested in bulk heterojunction solar cells. Preliminary studies show a great potential of these polymers for application in photovoltaics. Power conversion efficiency of up to 2.46% was achieved despite the dilution of the P3HT chains in the copolymer.

Large-Scale Alignment of Polymer Semiconductor Nanowires for Efficient Charge Transport via Controlled Evaporation of Confined Fluids

Long-range alignment of conjugated polymers is as critical as polymer chain packing for achieving efficient charge transport in polymer thin films used in electronic and optoelectronic devices. Here, the present study reports a facile, scalable strategy that enables the deposition of macroscopically aligned polymer semiconductor nanowire (NW)-array films with highly enhanced charge carrier mobility, using a modified controlled evaporative self-assembly (MCESA) technique. Organic field-effect transistors (OFETs) based on highly oriented poly(3-hexylthiophene) (P3HT)-NW films exhibit more than 10-fold enhancement of carrier mobility, with the highest mobility of 0.13 cm² V^-1 s^-1, compared to the OFETs based on pristine P3HT films. Significantly, large-area aligned P3HT NW-films, which are deposited over 12 arrays of transistors on a 4 in. wafer by an MCESA coating, result in lower device performance variation (i.e., standard deviation ≈ ±0.0172 (16%) cm² V^-1 s^-1) as well as an excellent average device performance (i.e., average charge mobility ≈ 0.11 cm² V^-1 s^-1), compared to those obtained using the conventional CESA coating, overcoming a critical challenge in the field of OFETs.

Investigation of the Effects of Non-Conjugated Co-Grafts on the Spectroelectrochemical and Photovoltaic Properties of Novel Conjugated Graft Copolymers Based on Poly(3-hexylthiophene)

A new type of polysiloxane copolymers, with conjugated–regioregular poly(3-hexylthiophene) (P3HT) and non-conjugated-poly(ethylene glycol) (PEG)-grafts have been synthesised, and their properties have been studied alongside those of the parent conjugated polymer (P3HT). Spectroelectrochemical and conductometric analyses revealed an early rise of the conductance of the polymers. Once spectral changes begin taking place, the conductance is stable, implying a loss of mobility of charge carriers, even though standard doping/dedoping patterns are observed. Prototype bulk heterojunction solar cells have been fabricated, based on P3HT/[6,6]-Phenyl-C61-butyric acid methyl ester (PCBM), as well as by substituting P3HT for each of the copolymers. The prototype solar cells achieved PCEs of up to 2.11%. This is one of the highest reported power conversion efficiency (PCE) for devices based on P3HT with low average molecular weight M_n = 12 kDa. Strong correlation between the structure of the copolymer and its photovoltaic performance was found. Elongation of PEG copolymer chain and the use of methyl group instead of terminal hydroxyl groups significantly improved photovoltaic performance.

Hybrid density functional study on the electronic structures and properties of P3HT-PbS and P3HT-CdS hybrid interface for photovoltaic applications

The efficiency of charge transport mainly depends on the interfacial energy level alignment between the conjugated polymer and the inorganic substrate. It provides an accurate understanding, predicting as well as controlling the optimal power conversion efficiency of various type of hybrid photovoltaic systems. In this article, we use hybrid functional (HSE06) to study the electronic structures and properties at the interface of poly(3-hexylthiophene)(P3HT)/CdS and P3HT/PbS for solar cell applications. We found that the dangling bonds at the inorganic surface introduce in-gap states and greatly reduce the device performance. We used pseudo-hydrogen atoms as the passivation agent to remove the dangling bonds and eliminate the in-gap states to construct the energy alignment at the hybrid interface. The calculated interfacial density of states reveal a better performance in P3HT/CdS, compared to P3HT/PbS. P3HT/CdS possesses a LUMO_P3HT /CBM_CdS and HOMO_P3HT /VBM_CdS energy offset large enough for sufficient exciton separation across the interface and prevents charge recombination. In contrast, the reason for low power conversion efficiency in P3HT/PbS lies on its HOMO_P3HT /VBM_PbS offset which is too small to break the exciton binding energy for charge separation. Moreover, we reported the dependency of the energy level alignment and open circuit voltage on the interfacial molecular orientations. Our DFT calculation can be used to predict candidate materials for the development of efficiency optoelectronic devices. © 2018 Wiley Periodicals, Inc.

A scanning probe microscopy study of nanostructured TiO2/poly(3-hexylthiophene) hybrid heterojunctions for photovoltaic applications

The nanoscale morphology of photoactive hybrid heterojunctions plays a key role in the performances of hybrid solar cells. In this work, the heterojunctions consist of a nanocolumnar TiO₂ surface covalently grafted with a monolayer of poly(3-hexylthiophene) (P3HT) functionalized with carboxylic groups (-COOH). Through a joint analysis of the photovoltaic properties at the nanoscale by photoconductive-AFM (PC-AFM) and surface photovoltage imaging, we investigated the physical mechanisms taking place locally during the photovoltaic process and the correlation to the nanoscale morphology. A down-shift of the vacuum level of the TiO₂ surface upon grafting was measured by Kelvin probe force microscopy (KPFM), evidencing the formation of a dipole at the TiO₂/P3HT-COOH interface. Upon in situ illumination, a positive photovoltage was observed as a result of the accumulation of photogenerated holes in the P3HT layer. A positive photocurrent was recorded in PC-AFM measurements, whose spatial mapping was interpreted consistently with the corresponding KPFM analysis, offering a correlated analysis of interest from both a theoretical and material design perspective.

Understanding the Intrinsic Carrier Transport in Highly Oriented Poly(3-hexylthiophene): Effect of Side Chain Regioregularity

The fundamental understanding of the influence of molecular structure on the carrier transport properties in the field of organic thermoelectrics (OTEs) is a big challenge since the carrier transport behavior in conducting polymers reveals average properties contributed from all carrier transport channels, including those through intra-chain, inter-chain, inter-grain, and hopping between disordered localized sites. Here, combining molecular dynamics simulations and experiments, we investigated the carrier transport properties of doped highly oriented poly(3-hexylthiophene) (P3HT) films with different side-chain regioregularity. It is demonstrated that the substitution of side chains can not only take effect on the carrier transport edge, but also on the dimensionality of the transport paths and as a result, on the carrier mobility. Conductive atomic force microscopy (C-AFM) study as well as temperature-dependent measurements of the electrical conductivity clearly showed ordered local current paths in the regular side chain P3HT films, while random paths prevailed in the irregular sample. Regular side chain substitution can be activated more easily and favors one-dimensional transport along the backbone chain direction, while the irregular sample presents the three-dimensional electron hopping behavior. As a consequence, the regular side chain P3HT samples demonstrated high carrier mobility of 2.9 ± 0.3 cm²/V·s, which is more than one order of magnitude higher than that in irregular side chain P3HT films, resulting in a maximum thermoelectric (TE) power factor of 39.1 ± 2.5 μW/mK² at room temperature. These findings would formulate design rules for organic semiconductors based on these complex systems, and especially assist in the design of high performance OTE polymers.

Solvent Additive-Assisted Anisotropic Assembly and Enhanced Charge Transport of π-Conjugated Polymer Thin Films

Charge transport in π-conjugated polymer films involves π-π interactions within or between polymer chains. Here, we demonstrate a facile solution processing strategy that provides enhanced intra- and interchain π-π interactions of the resultant polymer films using a good solvent additive with low volatility. These increased interactions result in enhanced charge transport properties. The effect of the good solvent additive on the intra- and intermolecular interactions, morphologies, and charge transport properties of poly(3-hexylthiophene) (P3HT) films is systematically investigated. We found that the good solvent additive facilitates the self-assembly of P3HT chains into crystalline fibrillar nanostructures by extending the solvent drying time during thin-film formation. As compared to the prior approach using a nonsolvent additive with low volatility, the solvent blend system containing a good solvent additive results in enhanced charge transport in P3HT organic field-effect transistor (OFET) devices [from ca. 1.7 × 10^-2 to ca. 8.2 × 10^-2 cm² V^-1 s^-1 for dichlorobenzene (DCB) versus 4.4 × 10^-2 cm² V^-1 s^-1 for acetonitrile]. The mobility appears to be maximized over a broad spectrum of additive concentrations (1-7 vol %), indicative of a wide processing window. Detailed analysis results regarding the charge injection and transport characteristics of the OFET devices reveal that a high-boiling-point solvent additive decreases both the contact resistance ( R_c) and channel resistance ( R_ch), contributing to the mobility enhancement of the devices. Finally, the platform presented here is proven to be applicable to alternative good solvent additives with low volatility, such as chlorobenzene (CB) and trichlorobenzene (TCB). Specifically, the mobility enhancement of the resultant P3HT films increases in the order CB (bp 131 °C) < DCB (bp 180 °C) < TCB (bp 214 °C), suggesting that solvent additives with higher boiling points provide resultant films with preferable molecular ordering and morphologies for efficient charge transport.

Fabrication of a P3HT-ZnO Nanowires Gas Sensor Detecting Ammonia Gas

In this study, an organic-inorganic semiconductor gas sensor was fabricated to detect ammonia gas. An inorganic semiconductor was a zinc oxide (ZnO) nanowire array produced by atomic layer deposition (ALD) while an organic material was a p-type semiconductor, poly(3-hexylthiophene) (P3HT). P3HT was suitable for the gas sensing application due to its high hole mobility, good stability, and good electrical conductivity. In this work, P3HT was coated on the zinc oxide nanowires by the spin coating to form an organic-inorganic heterogeneous interface of the gas sensor for detecting ammonia gas. The thicknesses of the P3HT were around 462 nm, 397 nm, and 277 nm when the speeds of the spin coating were 4000 rpm, 5000 rpm, and 6000 rpm, respectively. The electrical properties and sensing characteristics of the gas sensing device at room temperature were evaluated by Hall effect measurement and the sensitivity of detecting ammonia gas. The results of Hall effect measurement for the P3HT-ZnO nanowires semiconductor with 462 nm P3HT film showed that the carrier concentration and the mobility were 2.7 × 10¹⁹ cm⁻³ and 24.7 cm²∙V⁻¹∙s⁻¹ respectively. The gas sensing device prepared by the P3HT-ZnO nanowires semiconductor had better sensitivity than the device composed of the ZnO film and P3HT film. Additionally, this gas sensing device could reach a maximum sensitivity around 11.58 per ppm.

High-Efficiency Perovskite Solar Cell Based on Poly(3-Hexylthiophene): Influence of Molecular Weight and Mesoscopic Scaffold Layer

Here, we investigated the effect of the molecular weight (MW) of poly 3-hexylthiophene (P3HT) hole-transport material on the performance of perovskite solar cells (PSCs). We found that by increasing the MW the photovoltaic performances of the cells are enhanced leading to an improvement of the overall efficiency. P3HT-based PSCs with a MW of 124 kDa can achieve an overall average efficiency of 16.2 %, double with respect to the ones with a MW of 44 kDa. Opposite to spiro-OMeTAD-based PSCs, the photovoltaic parameters of the P3HT-based devices are enhanced by increasing the mesoporous TiO₂ layer thickness from 250 to 500 nm. Moreover, for a titania scaffold layer thickness of 500 nm, the efficiency of P3HT-based PSCs with high MW is larger than the spiro-OMeTAD based PSCs with the same scaffold layer thickness. Recombination reactions of the devices were also investigated by voltage decay and electrochemical impedance spectroscopy. We found that the relationship between P3HT MW and cell performance is related to the reduction of charge recombination and to the increase of the P3HT light absorption by increasing the MW.

Charge Transport in Intermixed Regions of All-Polymer Solar Cells Studied by Conductive Atomic Force Microscopy

Charge transport in intermixed regions of all-polymer solar cells based on a blend of poly(3-hexylthiophene) (P3HT; electron donor) with poly[2,7-(9,9-didodecylfluorene)-alt-5,5-(4',7'-bis(2-thienyl)-2',1',3'-benzothiadiazole)] (PF12TBT; electron acceptor) was studied by conductive atomic force microscopy (C-AFM). For a blend film fabricated from a chlorobenzene solution, intermixed regions were detected between the P3HT-rich and PF12TBT-rich domains. The overall hole current in the intermixed regions remained almost constant, both before and after thermal annealing at 80 °C, but it increased in the P3HT-rich domains. For a blend film fabricated from a chloroform solution, the entire observed area constituted an intermixed region, both before and after thermal annealing. The overall hole current in this film was significantly improved following thermal annealing at 120 °C. These finely mixed structures with efficient charge transport yielded a maximum power conversion efficiency of 3.5%. The local charge-transport properties in the intermixed region, as observed via C-AFM, was found to be closely related to the photovoltaic properties, rather than the bulk-averaged properties or topological features.

Stereoregular Brush Polymers and Graft Copolymers by Chiral Zirconocene-Mediated Coordination Polymerization of P3HT Macromers

Two poly(3-hexylthiophene) (P3HT) macromers containing a donor polymer with a polymerizable methacrylate (MA) end group, P3HT-CH₂-MA and P3HT-(CH₂)₂-MA, have been synthesized, and P3HT-(CH₂)₂-MA has been successfully homopolymerized and copolymerized with methyl methacrylate (MMA) into stereoregular brush polymers and graft copolymers, respectively, using chiral ansa-zirconocene catalysts. Macromer P3HT-CH₂-MA is too sterically hindered to polymerize by the current Zr catalysts, but macromer P3HT-(CH₂)₂-MA is readily polymerizable via either homopolymerization or copolymerization with MMA in a stereospecific fashion with both C₂-ligated zirconocenium catalyst 1 and Cs-ligated zirconocenium catalyst 2. Thus, highly isotactic (with mm% ≥ 92%) and syndiotactic (with rr% ≥ 93%) brush polymers, it-PMA-g-P3HT and st-PMA-g-P3HT, as well as well-defined stereoregular graft copolymers with different grafted P3HT densities, it-P(M)MA-g-P3HT and st-P(M)MA-g-P3HT, have been synthesized using this controlled coordination-addition polymerization system under ambient conditions. These stereoregular brush polymers and graft copolymers exhibit both thermal (glass and melting) transitions with Tg and Tm values corresponding to transitions within the stereoregular P(M)MA and crystalline P3HT domains. Acceptor molecules such as C60 can be effectively encapsulated inside the helical cavity of st-P(M)MA-g-P3HT to form a unique supramolecular helical crystalline complex, thus offering a novel strategy to control the donor/acceptor solar cell domain morphology.

Ethylene Detection Based on Organic Field-Effect Transistors With Porogen and Palladium Particle Receptor Enhancements

Ethylene sensing is a highly challenging problem for the horticulture industry because of the limited physiochemical reactivity of ethylene. Ethylene plays a very important role in the fruit life cycle and has a significant role in determining the shelf life of fruits. Limited ethylene monitoring capability results in huge losses to the horticulture industry as fruits may spoil before they reach the consumer, or they may not ripen properly. Herein we present a poly(3-hexylthiophene-2,5-diyl) (P3HT)-based organic field effect transistor as a sensing platform for ethylene with sensitivity of 25 ppm V/V. To achieve this response, we used N-(tert-Butoxy-carbonyloxy)-phthalimide and palladium particles as additives to the P3HT film. N-(tert-Butoxy-carbonyloxy)-phthalimide is used to increase the porosity of the P3HT, thereby increasing the overall sensor surface area, whereas the palladium (<1 μm diameter) particles are used as receptors for ethylene molecules in order to further enhance the sensitivity of the sensor platform. Both modifications give statistically significant sensitivity increases over pure P3HT. The sensor response is reversible and is also highly selective for ethylene compared to common solvent vapors.

Investigation of the Effect of Thermal Annealing on Poly(3-hexylthiophene) Nanofibers by Scanning Probe Microscopy: From Single-Chain Conformation and Assembly Behavior to the Interfacial Interactions with Graphene Oxide

Poly(3-hexylthiophene) (P3HT) has been widely used in devices owing to its excellent properties and structural features. However, devices based on pure P3HT have not exhibited high performance. Strategies, such as thermal annealing and surface doping, have been used to improve the electrical properties of P3HT. In this work, different from previous studies, the effect of thermal annealing on P3HT nanofibers are examined, ranging from the single polymer chain conformation to chain packing, and the interfacial interactions with graphene oxide (GO) at nanoscale dimensions, by using scanning tunneling microscopy (STM), atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). High-resolution STM images directly show the conformational changes of single polymer chains after thermal annealing. The morphology of P3HT nanofibers and the surface potential changes of the P3HT nanofibers and GO is further investigated by AFM and KPFM at the nanoscale, which demonstrate that the surface potentials of P3HT decrease, whereas that of GO increases after thermal annealing. All of the results demonstrate the stronger interfacial interactions between P3HT and GO occur after thermal treatments due to the changes in P3HT chain conformation and packing order.

Parasitic Capacitance Effect on Dynamic Performance of Aerosol-Jet-Printed Sub 2 V Poly(3-hexylthiophene) Electrolyte-Gated Transistors

Printed, low-voltage poly(3-hexylthiophene) (P3HT) electrolyte-gated transistors (EGTs) have favorable quasi-static characteristics, including sub 2 V operation, carrier mobility (μ) of 1 cm²/(V s), ON/OFF current ratio of 10⁶, and static leakage current density of 10^-6 A/cm². Here we study the dynamic performance of P3HT EGTs in which the semiconductor, dielectric, and gate electrode were deposited using aerosol-jet printing; the source and drain electrodes were patterned by conventional microlithography. With a source-to-drain separation of 2.5 μm, the highest theoretical achievable switching frequency is ∼10 MHz, assuming the movement of charge through the semiconductor is the limiting step. However, the measured maximum switching frequency of P3HT EGTs to date is ∼1 kHz, implying that another process is slowing the response. By systematically varying the device geometry, we show that the frequency is limited by the capacitance between the gate and drain (i.e., parasitic capacitance). The traditional scaling of switching time with the square of channel length (L) does not hold for P3HT EGTs. Rather, minimizing the size of the drain electrode increases the maximum switching speed. We achieve 10 kHz for P3HT EGTs with source/drain electrode dimensions of 2.5 μm × 50 μm and channel dimensions of 2.5 μm × 50 μm. Further improvements will require additional shrinkage of electrode dimensions as well as consideration of other factors such as ion gel thickness and carrier mobility.

Controlled Growth of Well-Defined Conjugated Polymers from the Surfaces of Multiwalled Carbon Nanotubes: Photoresponse Enhancement via Charge Separation

The installation of heterojunctions on the surfaces of carbon nanotubes (CNTs) is an effective method for promoting the charge separation processes needed for CNT-based electronics and optoelectronics applications. Conjugated polymers are proven state-of-the-art candidates for modifying the surfaces of CNTs. However, all previous attempts to incorporate conjugated polymers to CNTs resulted in unordered interfaces. Herein we show that well-defined chains of regioregular poly(3-hexylthiophene) (P3HT) were successfully grown from the surfaces of multiwalled CNTs (MWNTs) using surface-initiated Kumada catalyst-transfer polycondensation. The polymerization was found to proceed in a controlled manner as chains of tunable lengths were prepared through variation of the initial monomer-to-initiator ratio. Moreover, it was determined that large-diameter MWNTs afforded highly ordered P3HT aggregates, which exhibited a markedly bathochromically shifted optical absorption due to a high grafting density induced planarization of the polymer chains. Using ultrafast spectroscopy, the heterojunctions formed between the MWNTs and P3HT were shown to effectively overcome the binding energy of excitons, leading to photoinduced electron transfer from P3HT to MWNTs. Finally, when used as prototype devices, the individual MWNT-g-P3HT core-shell structures exhibited excellent photoresponses under a low illumination density.

Toward Uniformly Dispersed Battery Electrode Composite Materials: Characteristics and Performance

Battery electrodes are complex mesoscale systems comprised of electroactive components, conductive additives, and binders. In this report, methods for processing electrodes with dispersion of the components are described. To investigate the degree of material dispersion, a spin-coating technique was adopted to provide a thin, uniform layer that enabled observation of the morphology. Distinct differences in the distribution profile of the electrode components arising from individual materials physical affinities were readily identified. Hansen solubility parameter (HSP) analysis revealed pertinent surface interactions associated with materials dispersivity. Further studies demonstrated that HSPs can provide an effective strategy to identify surface modification approaches for improved dispersions of battery electrode materials. Specifically, introduction of surfactantlike functionality such as oleic acid (OA) capping and P3HT-conjugated polymer wrapping on the surface of nanomaterials significantly enhanced material dispersity over the composite electrode. The approach to the surface treatment on the basis of HSP study can facilitate design of composite electrodes with uniformly dispersed morphology and may contribute to enhancing their electrical and electrochemical behaviors. The conductivity of the composites and their electrochemical performance was also characterized. The study illustrates the importance of considering electronic conductivity, electron transfer, and ion transport in the design of environments incorporating active nanomaterials.

A Physicochemical Approach Toward Extending Conjugation and the Ordering of Solution-Processable Semiconducting Polymers

Poly(3-hexylthiophene)s (P3HTs) were synthesized with a well-controlled molecular weight (Mw) and degree of regioregularity; additionally, π-conjugated P3HT structures in both solutions and films were systematically investigated. Conjugated P3HT phases in spin-cast films significantly changed from ordered nanorods, -fibrils, and -ribbons to less-ordered granules, depending on the conformation of the P3HT chains in solutions. The chain conformations could be physicochemically adjusted by modifying chain lengths (from 5 to 45 kDa), solvents, and ultrasonication. Highly extended conformations of the P3HT in ultrasound-treated solutions yielded longer degree of conjugation both the intra- and intermolecularly. When toluene was used as a marginal solvent, ultrasonicated 0.1 wt % 29 kDa P3HT solutions could be used to yield highly ordered aggregates in spin-cast films, including nanoribbons or nanosheets, with field-effect mobility (μFET) up to ∼0.1 cm(2) V(-1) s(-1) being measured for organic field-effect transistors (OFETs). However, ultrasonicated chloroform systems with good P3HT solubility (for P3HT Mw ≥ 20 kDa) yielded featureless conducting layers even at 0.4 wt % P3HT content. However, these film-based OFETs yielded μFET values up to 0.04 cm(2) V(-1) s(-1), which were much greater than 0.004 cm(2) V(-1) s(-1) for the nonultrasonicated systems.

Effects of Regioregularity and Molecular Weight on the Growth of Polythiophene Nanofibrils and Mixes of Short and Long Nanofibrils To Enhance the Hole Transport

Morphological control over polythiophenes has been widely studied; however the impacts of regioregularity (RR) and molecular weight (MW) on their structural development have not been investigated systematically. This study examined a representative polythiophene, poly(3-hexylthiophene) (P3HT), to reveal that small differences in the RR can produce a large difference in the growth of nanofibrils. Low-RR P3HTs generated neat long nanofibrils (LNFs), whereas high-RR P3HTs formed short nanofibrils (SNFs). This study identified a critical RR (96-98%) depending on their MW, below which P3HT grew into LNFs and above which P3HT grew into SNFs. This study also found that the mixing ratio between high-RR P3HT and a low-RR P3HT in the solution phase is strongly correlated with the relative populations of SNF and LNF in the coated film. This study suggested that mixing high-RR and low-RR polymers may be a good strategy to optimize the electrical properties of polythiophenes for target applications. As an example, a mixture of high-RR (75%) P3HT and low-RR P3HT (25%) improved considerably the power conversion efficiency of bulk heterojunction polymer solar cells compared with the values obtained from the pure high-RR P3HT and the pure low-RR P3HT.