Doped State Research Articles

Matching P- and N-type Organic Electrochemical Transistor Performance Enables a Record High-gain Complementary Inverter.

The charge transport of channel materials in n-type organic electrochemical transistors (OECTs) is greatly limited by the adverse effects of electrochemical doping, posing a long-standing puzzle for the community. Herein, ann-type conjugated polymer with glycolated side chains (n-PT3) is introduced. This polymer can adapt to electrochemical doping and create more organized nanostructures, mitigating the adverse effects of electrochemical doping. This unique characteristic gives n-PT3 excellent charge transport in the doped state and reversible ion storage, making it highly suitable as an n-type organic mixed ionic-electronic conducting (OMIEC) material. n-PT3 exhibits a high electron mobility of µ ≈ 1.0 cm2 V-1 s-1 and a figure of merit value of µC* ≈ 100 F cm-1 V-1 s-1, representing one of the best results for n-type OMIEC materials. A new p-type OMIEC polymer has been synthesized as the channel material for constructing a complementary inverter to match the n-type OECT channel layer based on n-PT3. As a result, a voltage gain value of up to 307 VV-1 has been achieved, which is a record value for sub-1V complementary inverters based on OECTs. This work offers valuable insights into designing electrochemical doping adaptive n-type OMIEC materials and fabricating high-gain organic complementary inverters.

Power-dependent and ultrafast spectroscopic studies of Ag ion-doped colloidal CdSe nanoplatelets.

Atomically precise two-dimensional (2D) semiconductor nanoplatelets (NPLs) are found to be promising materials for next-generation optoelectronic devices due to their excellent optical properties. However, energy loss through phonon emission significantly causes problems in achieving efficient performance. Power-dependent steady-state spectroscopy and ultrafast spectroscopic studies have been performed to understand the influence of Ag ions on ultrafast carrier dynamics and thermalization processes in colloidal CdSe NPLs. An ultrafast transient absorption spectroscopic study shows that the rise time is faster from 410 fs to ∼160 fs after 11% Ag doping in CdSe NPLs. The dopant states act as a trap for the charge carriers that facilitate faster relaxation of electrons in these dopant states. The bleach decay time constant (τ1r) changes from 5 ps to 800 fs, changing the dopant concentration from 0 to 11% Ag, indicating the charge carrier separation through an intra-band dopant-mediated state. Power-dependent steady-state photoluminescence spectroscopic study reveals that the thermalization rate reduces from 159.9 ± 9 mW K-1 cm-2 to 27.35 ± 2 mW K-1 cm-2 after Ag doping into CdSe NPLs due to the phonon bottleneck effect (PBE). Reducing the thermalization rate and charge carrier separation due to incorporating Ag dopant is beneficial for efficient optoelectronic devices.

Corrigendum to “Effect of dopant oxidation states on enhanced low ppm CO sensing by copper doped zinc oxide” [Mater. Chem. Phys. 295 (2023) 127047

Corrigendum to “Effect of dopant oxidation states on enhanced low ppm CO sensing by copper doped zinc oxide” [Mater. Chem. Phys. 295 (2023) 127047

Highly Porous Nitrogen and Phosphorus Dual-Doped Carbon with Increased Phosphorus Content As an Efficient Oxygen Reduction Electrocatalyst

Fuel cells and metal-air batteries have attracted the attention of many researchers because of their high power density and large energy density. Carbon materials are typically used as catalyst supports and conductive agents at the cathodes in fuel cells and metal-air batteries. However, pure carbon exhibits low electrocatalytic activity for the oxygen reduction reaction (ORR) at the cathodes. Single doping of heteroatoms, such as nitrogen and phosphorus, has been investigated as a simple method to improve the ORR activity of carbon materials. Moreover, compared with single doping, dual doping of nitrogen and phosphorus can further enhance the ORR performance due to the synergetic effect of the dopants [1]. Acetylene blacks (ABs) are readily available and widely used in industry for pigments, reinforcing rubber, and battery electrodes. However, the content of heteroatoms doped into AB by conventional heat treatment is low [2]. Recently, mechanochemical treatments have received increasing attention because they are more robust and simpler than conventional methods. Some studies have been conducted on solid-gas mechanochemical treatment under an air atmosphere as a nitrogen doping method for graphite and graphite-based materials [3]. In this study, nitrogen and phosphorus dual-doped carbon (NPC) was synthesized by a two-step method: solid-gas mechanochemical treatment using a planetary ball mill at a rotation speed of 600 rpm for 1 h to prepare nitrogen-doped carbon (NC), followed by heat treatment with ammonium dihydrogen phosphate (ADP) at 800 °C for 12 h to dope the NC with phosphorus. For comparison, phosphorus-doped carbon (PC) was synthesized by heat treatment of AB with ADP at 800 °C for 12 h.X-ray photoelectron spectroscopy was used to identify the doping states and concentrations of the samples. NPC has high concentrations of nitrogen (1.60 at%) and phosphorus (1.91 at%). In contrast, PC has a low phosphorus concentration (0.14 at%). Scanning electron microscopy revealed that mechanochemical treatment using a ball mill broke the particles and reduced their size from 35 nm in AB to approximately 10 nm in NC and NPC. The surface areas of NC and NPC significantly increased to 424 m2 g−1 and 540 m2 g−1, respectively, compared with that of AB (64.7 m2 g−1), mainly due to particle size reduction. Furthermore, NC and NPC exhibit high porosity with a maximum at 3.6 nm (Fig. 1a). The primary pores of NC and NPC constitute spaces between the particles. Electrochemical measurements were performed using a rotating disk electrode (RDE) in O2-saturated 1.0 M KOH. Linear sweep voltammetry curves of samples at an RDE rotation speed of 1600 rpm are shown in Fig. 1b. NC exhibits a much higher kinetic current density of 1.71 mA cm−2 at −0.15 V vs. Hg/HgO calculated from a mass transport correction of RDE than AB (0.04 mA cm−2), suggesting that the doped nitrogen and high porosity in NC significantly promote the ORR process. Furthermore, NPC shows 2.4 times higher kinetic current density of 4.14 mA cm−2 than NC, indicating that additional phosphorus doping into NC can enhance the ORR activity. Owing to the highly porous structure in NC, phosphorus atoms can be effectively doped into the carbon matrix during heat treatment, which may lead to the generation of abundant active sites for the ORR in NPC.

Electrochemical C–H Arylation of Polythiophenes By Using Aryldiazonium Salts

Electrochemical post-functionalization is a polymer reaction method in which a nucleophile (or electrophile) attacks the doping state of a π-conjugated polymer generated by applying a potential to the polymer film1,2). This reaction scheme faces various challenges, including the limitation that only conducting polymers can be used as a precursor in the solid state. In order to solve this problem, development of a liquid-phase electrochemical post-functionalization is required. However, it is also known that electron transfer between electrodes and dissolved polymers does not proceed efficiently. Therefore, in this study, we developed a liquid-phase electrochemical post-functionalization that does not rely on direct electron transfer between polymers and electrodes. This method is expected to broaden the application of the electrochemical post-functionalization. Based on the report on the electrochemical C–H arylation of heteroaromatic rings by using the aryl radicals produced by the reduction of aryldiazonium salts3), we investigated to apply the reaction for the C–H arylation of poly(3-hexylthiophene) (P3HT). This approach allows for direct C–H bond functionalization without the need for introducing a functional group beforehand. Moreover, the environmentally friendly electric energy is used as the reaction driving force, avoiding need of a metal catalyst required in conventional methods4,5). Constant current electrolysis of P3HT dissolved in chlorobenzene with an aryl diazonium salt was conducted, and the introduction of an aryl group into the 4-position of the thiophene ring was confirmed by 1H NMR. However, the 1H NMR spectrum of the product (P3HT-Ar) suggested that an unsubstituted phenyl group derived from chlorobenzene was also introduced. Subsequent solvent investigation showed that using a mixed solvent (CHCl3/CH2Cl2 = 2:1) suppressed this side reaction. In addition, the formation of aryldiazonium salts in-situ, by adding 4-nitroaniline and tBuONO, yielded products with the higher degree of functionalization compared to the direct addition of aryldiazonium salts. Current density studies showed that at low current density conditions suppressed side reactions and improved the degree of functionalization. Furthermore, the degree of functionalization could be controlled to a certain range from 0% to 30%, by adjusting the charge passed. It was also possible to introduce 4-trifluoromethylphenyl group in this protocol. As a reference condition, when unsubstituted aniline without an electron-withdrawing group was used as a substrate, no arylation reaction proceed. Finally, the photophysical and electrochemical properties of P3HT-Ar were investigated. CV measurements of P3HT and P3HT-Ar with different degree of functionalization showed the oxidation potential shifted positively with increasing the degree of functionalization. The reduction peak, which did not appear in P3HT, was observed for P3HT-Ar. Furthermore, UV-vis absorption spectroscopy revealed that the maximum absorption wavelength (λmax abs) shortened as the degree of functionalization increased. These are possibly induced by the electron-withdrawing property of the 4-nitrophenyl group and the decrease in the effective π-conjugation length due to the main chain twisting. The fluorescence quantum yield significantly decreased with increasing the degree of functionalization, attributed to the fluorescence quenching effect of the 4-nitrophenyl group.Reference1) S. Inagi, T. Fuchigami, Macromol. Rapid Commun., 2014, 35, 854.2) T. Kurioka, S. Inagi, Chem. Rec., 2021, 21, 2107.3) D. Hata, M. Tobisu, T. Amaya, Bull. Chem. Soc. Jpn., 2018, 91, 1749.4) Y. Li, G. Vamvounis, J. Yu, S. Holdcroft, Macromolecules, 2001, 34, 3130.5) H. Goto, B. Ochiai, Y. Matsumura, Electrochemistry, 2023, 91,112004.6) D. Giri, S. N. Islam, S. K. Patra, Polymer, 2018, 134, 242. Figure 1

Self-Assembly Synthesis of Oxygen and Sulfur Co-Doped Porous Graphitic Carbon Nitride Nanosheets for Boosting CO2 Photoreduction.

Graphitic carbon nitride (CN) has garnered considerable attention in the field of visible-light CO2 photoreduction, but its efficiency remains limited by the intrinsic π-conjugated skeleton. Here, O and S were co-doped CN (O, S/CN) by a facile "hydrolysis + calcination" approach to modulate the physicochemical and electronic structure. Distinctive from S doped CN (SCN), O, S/CN owned porous layer structure with several nanosheets and less SO4 2- groups on the surface. The amount of heteroatom-doping was achieved by changing the hydrothermal temperature. The optimum O, S/CN-80 achieved moderate CO production rate of 1.29 μmol g-1 h-1, which was 3.79 times as much as SCN (0.34 μmol g-1 h-1). The O and most S atoms were substitutionally doped and the effect of S doped state on the improved efficiency of CO generation in O, S/CN was also explored based on the theoretical calculations. This work provides an inspiration to develop efficient dual-doped CN photocatalysts for photocatalytic CO2 reduction.

Enhancing Carrier Behavior via Controlled Molecular Film Formation Engineering Leads to Significant Improvement in Electroluminescence

AbstractThe quality of organic thin films critically influences carrier dynamics in organic semiconductors. In neat/doped films, even tiny voids can be penetrated by water or oxygen molecules to create charge‐trap states called water/oxygen‐induced traps that significantly hinder carrier mobility. While the water/oxygen‐induced traps in non‐doped films and crystalline states have been investigated comprehensively, there is a lack of thorough examination regarding their properties in the doped state. Therefore, there is a high demand for a molecular design strategy that effectively modulates the molecular stacking behavior in doped films and practical devices and enhances the quality of these films. Herein, we proposed a versatile molecular design principle that enables the formation of “nano‐cluster” structures on both the surface and interior of doped films in target molecule 10‐(4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐1′‐(4‐fluorophenyl)‐10H‐spiro[acridine‐9,9′‐xanthene] (DspiroO‐F‐TRZ), which is modified with a fluorophenyl group. These “nano‐cluster” structures exhibit more uniform shapes within doped films and effectively reduce defective state densities while enhancing carrier injection and transport properties, ultimately improving device performance. Notably, TADF‐OLED based on DspiroO‐F‐TRZ demonstrates nearly twice as much efficiency as its control counterpart due to contributions from ′nano‐cluster′ structure enhancements toward improved electroluminescence performance.

Enhancing Carrier Behavior via Controlled Molecular Film Formation Engineering Leads to Significant Improvement in Electroluminescence.

The quality of organic thin films critically influences carrier dynamics in organic semiconductors. In neat/doped films, even tiny voids can be penetrated by water or oxygen molecules to create charge-trap states called water/oxygen-induced traps that significantly hinder carrier mobility. While the water/oxygen-induced traps in non-doped films and crystalline states have been investigated comprehensively, there is a lack of thorough examination regarding their properties in the doped state. Therefore, there is a high demand for a molecular design strategy that effectively modulates the molecular stacking behavior in doped films and practical devices and enhances the quality of these films. Herein, we proposed a versatile molecular design principle that enables the formation of "nano-cluster" structures on both the surface and interior of doped films in target molecule 10-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-1'-(4-fluorophenyl)-10H-spiro[acridine-9,9'-xanthene] (DspiroO-F-TRZ), which is modified with a fluorophenyl group. These "nano-cluster" structures exhibit more uniform shapes within doped films and effectively reduce defective state densities while enhancing carrier injection and transport properties, ultimately improving device performance. Notably, TADF-OLED based on DspiroO-F-TRZ demonstrates nearly twice as much efficiency as its control counterpart due to contributions from 'nano-cluster' structure enhancements toward improved electroluminescence performance.

Regulating Peripheral Nitrogen Dopants in Single-Atom Catalysts to Enhance Propane Dehydrogenation.

For single-atom catalysts (SACs), the dopants situated near the metal site have demonstrated a significant impact on the catalytic properties. However, the effect of dopants situated further away from the metal centers and their working mechanisms remain to be elucidated. Herein, we conduct density functional theory-driven studies on regulating the peripheral nitrogen dopants in graphene-based SACs, with a particular focus on Ir1 SAC, for propane dehydrogenation (PDH). It is found that increasing the distance between the N dopant and the Ir1 site results in a different energy change for the reaction process compared to the dense doping models with only first and second-shell N species. The proposed stochastic doping models demonstrate statistically that increasing the N dopant in farther shells not only enhances the activity of Ir1 but also maintains a high selectivity for propene, which is verified by experimental tests. The modulation of the d-band center of Ir1 by stochastic N dopants effectively modifies the binding strength of reaction intermediates, thereby enabling the optimization of the potential energy surface of PDH. These results deepen the understanding of dopant states around metal sites and provide an important implication for the doping engineering in heterogeneous catalysis.

Tailored Environment-Friendly Reverse Type-I Colloidal Quantum Dots for a Near-Infrared Optical Synapse and Artificial Vision System.

Colloidal quantum dots (QDs) are emerging as potential candidates for constructing near-infrared (NIR) photodetectors (PDs) and artificial optoelectronic synapses due to solution processability and a tunable bandgap. However, most of the current NIR QDs-optoelectronic devices are still fabricated using QDs with incorporated harmful heavy metals of lead (Pb) and mercury (Hg), showing potential health and environment risks. In this work, we tailored eco-friendly reverse type-I ZnSe/InP QDs by copper (Cu) doping and extended the photoresponse from the visible to NIR region. Transient absorption spectroscopy analysis revealed the presence of Cu dopant states in ZnSe/InP:Cu QDs that facilitated the extraction of photogenerated charge carriers, leading to an enhanced photodetection performance. Specifically, under 400 nm illumination, the Cu-doped ZnSe/InP QDs-based PDs presented a broadband photodetection ranging from ultraviolet (UV) to NIR, with a responsivity of 70.5 A W-1 and detectivity of 2.8 × 1011 Jones, surpassing those of the undoped ZnSe/InP QDs-based PDs (49.4 A W-1 and 1.9 × 1011 Jones, respectively). More importantly, the ZnSe/InP:Cu QDs-PDs demonstrated various synapse-like characteristics of short-term plasticity (STP), long-term plasticity (LTP), and learning-forging-relearning under NIR light illumination, which were further used to construct PD array devices for simulating the artificial visual system that is available in prospective optical neuromorphic applications.

N‐Type Molecular Thermoelectrics Based on Solution‐Doped Indenofluorene‐Dimalononitrile: Simultaneous Enhancement of Doping Level and Molecular Order

AbstractThe development of n‐type organic thermoelectric materials, especially π‐conjugated small molecules, lags far behind their p‐type counterparts, due primarily to the scarcity of efficient electron‐transporting molecules and the typically low electron affinities of n‐type conjugated molecules that leads to inefficient n‐doping. Herein, the n‐doping of two functionalized (carbonyl vs dicyanovinylene) indenofluorene‐based conjugated small molecules, 2,8‐bis(5‐(2‐octyldodecyl)thien‐2‐yl)indeno[1,2‐b]fluorene‐6,12‐dione (TIFDKT) and 2,2′‐(2,8‐bis(3‐alkylthiophen‐2‐yl)indeno[1,2‐b]fluorene‐6,12‐diylidene)dimalononitrile (TIFDMT) are demonstrated, with n‐type dopant N‐DMBI. While TIFDKT shows decent miscibility with N‐DMBI, it can be hardly n‐doped owing to its insufficiently low LUMO. On the other hand, TIFDMT, despite a poorer miscibility with N‐DMBI, can be efficiently n‐doped, reaching a respectable electrical conductivity of 0.16 S cm−1. Electron paramagnetic resonance measurements confirm the efficient n‐doping of TIFDMT. Based on density functional theory (DFT) calculations, the LUMO frontier orbital energy of TIFDMT is much lower, and its wave function is more delocalized compared to TIFDKT. Additionally, the polarons are more delocalized in the n‐doped TIFDMT. Remarkably, as indicated by the grazing‐incidence wide‐angle X‐ray scattering (GIWAXS), the molecular order for TIFDMT thin‐film is enhanced by n‐doping, leading to more favorable packing with edge‐on orientation and shorter π‐π stacking distances (from 3.61 to 3.36 Å). This induces more efficient charge transport in the doped state. Upon optimization, a decent thermoelectric power factor of 0.25 µWm−1K−2 is achieved for n‐doped TIFDMT. This work reveals the effect of carbonyl vs dicyanovinylene on the n‐doping efficiency, microstructure evolution upon doping and thermoelectric performance, offering a stepping stone for the future design of efficient n‐type thermoelectric molecules.

Charge Transfer‐Induced SERS Enhancement of MoS2/Dopants Dependent on their Interaction Difference

Abstract2D transition metal dichalcogenide materials have attracted increasing attention as active surface‐enhanced Raman spectroscopy (SERS) platforms. In this study, the influence of n‐ and p‐type doping of exfoliated MoS2 (exMoS2) hybrids on the SERS performance is investigated, employing Rhodamine 6G (R6G) as a probe molecule. It is demonstrated that n‐doped exMoS2 hybrids (exMoS2 mixed with C60, graphene, and sodium dodecyl sulfate) exhibit enhanced SERS intensities, while p‐doping (exMoS2 mixed with TCNQ) resulted in inhibited SERS enhancement. A key discovery is the linear relationship between Raman enhancement of MoS2/dopant hybrids and the difference in their LUMO energy levels, which dictate the degree and direction of charge transfer. Interestingly, MC60‐4, a C60‐doped hybrid, deviates from the linear relationship, displaying remarkable SERS enhancement owing to its chemical interaction and unique Raman scattering activity. The findings provide critical insights into the SERS enhancement behavior of doped MoS2, facilitating precise tuning of SERS intensities by manipulating the MoS2 doping state.

Strategy to optimize the broadband near-infrared emission based on Eu2+-doped sulfureted garnet phosphors toward emerging spectroscopy applications

Eu2+-doped near-infrared (NIR) emitting phosphors, known for their high efficiency, broadband emission and spectral tunability, have gained much attention. However, achieving efficient NIR emission based on Eu2+ remains a challenge due to the co-existence of Eu3+, especially in materials (i.e. garnets and apatites) containing trivalent lanthanide cations. In this study, a Eu2+ doped sulfureted NIR-emitting garnet phosphor Ca3(Sc, Eu)2Si3(O, S)12: Eu2+ is successfully designed and synthesized. Notably, a strategy for regulating the initial valence state of dopants is proposed by using prepared EuS instead of the conventional Eu2O3 as raw material, enhancing the NIR emission by 135 %. Moreover, a sulfuration strategy is further introduced to enhance the NIR-emitting intensity and internal quantum efficiency by 192 % and 167.8 %, and to improve thermal stability by 154 % at 120 °C. The luminescence origin of the unusual broadband NIR emission is re-examined through chemical unit co-substitution strategy by introducing [Al3+Hf4+] to replace [Sc3+Si4+] ion pairs. Meanwhile, the spectral regulation and the performance optimization mechanism are systematically discussed. Finally, a green light pumped NIR LED device with a photoelectric efficiency of 9.43 %@100 mA and output power of 22.74 mW@100 mA is fabricated, showing remarkable potential in nondestructive testing and biomedical imaging applications.

An ab-initio investigation of physical characteristics of GdSc1-xTMxO3(TM=Ti; x=0.25, 0.5, 0.75) for photo influenced (NIR)memory storage and allied devices

In the present study, we have computed the structural, electronic, and optical characteristics of pristine GdScO3 and GdSc1-xTMxO3 (TM = Ti; x = 0.25, 0.5, 0.75) for improved performance of Resistive Random Access Memory (RRAM) devices. All calculations have been performed using the Tran Balha-modified Becke Johnson (TB-mBJ) approximation within the framework of the WEIN2K simulation package. Herein, the effect of Ti-dopant (transition metal, i.e., TM) with varying concentrations has been observed, especially in tuning the energy band gap. The structural analysis of composites reveals structural stability and a significant reduction in bulk modulus with increasing dopant concentration, leading to enhanced electrical conductivity. The band structure analysis reveals that the band gap tends to decrease with increasing concentrations of Ti-dopant.As regards total density of states (TDOS), it has been found that with increasing concentrations of Ti, dopant extra states appear in the conduction band. This is the reason behind the formation of the conducting filaments (CF) within the active layer of RRAM devices. The partial density of states (PDOS) elaborates that for all studied composites, the formation of the conduction band (C.B.) and valence band (V.B.) is a consequence of the hybridization of Sc-3d, Gd-5d, and Ti-4d states, along with the minute contribution of O-2p states. Optical characteristics disclose the photoresponse of all studied composites, wherein GdSc0.25Ti0.75O3 exhibits wide range absorption, henceforth making it a making it a more suitable candidate for photoinfluencing, especially in near infrared (NIR) RRAM devices.

Enhanced Neurotransmitter Detection with Biorecognition Element-Functionalized Organic Electrochemical Transistors

The United States National Academies of Science and Engineering have issued a grand challenge to “reverse-engineer the brain”. Addressing this challenge requires a more complete understanding of how connections between individual neurons and groups of neurons are formed and maintained, as well as a more thorough elucidation of the signaling processes that drive neural network optimization. However, to achieve these goals, it is first necessary to develop the appropriate fundamental tools and protocols for adaptive biointerfacing, bottom-up neuroscience, and neuromodulation.To address this challenge, our research team has developed neurotransmitter-specific biosensors based on organic electrochemical transistors (OECT), which are electrolyte-gated devices that permit large signal amplification, ionic-to-electronic signal transduction, and controllable variable resistance. Given that their porous channel materials enable volumetric interaction with the adjacent electrolyte, OECT offer increased detection sensitivity compared to other electrolyte-gated devices such as field-effect transistors (FET). Although these OECT devices have demonstrated utility in a wide range of applications, from neuromorphic computing to bioelectronic devices, they are still in an early stage of development.We report enhanced electrochemical sensing of dopamine, mediated by functionalizing the OECT gate electrode with dopamine-specific biorecognition elements (BRE, i.e., aptamers). To optimize these devices, our team tested a variety of electrode functionalization approaches (e.g. alkane-thiol or silane chemistry, layer-by-layer, and covalent modification). The operational principle of BRE-functionalized OECT gate electrode biosensing is based on changes in gate electrode surface potential caused by target-binding to the BRE. When the target binds to the BRE, the event alters the capacitance at the surface of the functionalized gate electrode. The change in surface potential at the gate electrode shifts the applied potential on the OECT channel, which alters the doping state of the OECT channel. The channel materials are mixed ionic/electronic conductors, so changes in the doping state of the channel will directly affect the transconductance of the channel, which alters the OECT transfer characteristic and thereby permits sensing. The large transconductance of the OECT channel allows small changes in doping state to amplify the signal caused by binding of the target to the surface-attached BRE.In this study, we directly compare the dopamine biosensing performance of BRE-functionalized gold electrodes tested in two different sensing configurations:(i) traditional amperometric biosensor with a BRE-functionalized working electrode(ii) OECT with BRE-functionalized gate electrodeWe confirm the operational principles outlined above, and quantitatively assess the biosensing performance through a variety of analytical and electroanalytical techniques, such as cyclic voltammetry, open-circuit potentiometry, electrochemical impedance spectroscopy (EIS), square-wave and differential pulse voltammetry (DPV), and electrochemical quartz crystal microbalance (EQCM). We also compare the observed concentration-dependent changes in OECT transfer characteristics to the changes predicted by a theoretical analysis of surface potential.Finally, we will present the steps we have taken to implement these devices within organ-on-a-chip systems, both for traditional neurotransmitter biosensing and to demonstrate the utility of our devices for studying the formation and longitudinal evolution of neural networks within in vitro neuronal colonies.

Non-equilibrium transport in polymer mixed ionic–electronic conductors at ultrahigh charge densities

Conducting polymers are mixed ionic–electronic conductors that are emerging candidates for neuromorphic computing, bioelectronics and thermoelectrics. However, fundamental aspects of their many-body correlated electron–ion transport physics remain poorly understood. Here we show that in p-type organic electrochemical transistors it is possible to remove all of the electrons from the valence band and even access deeper bands without degradation. By adding a second, field-effect gate electrode, additional electrons or holes can be injected at set doping states. Under conditions where the counterions are unable to equilibrate in response to field-induced changes in the electronic carrier density, we observe surprising, non-equilibrium transport signatures that provide unique insights into the interaction-driven formation of a frozen, soft Coulomb gap in the density of states. Our work identifies new strategies for substantially enhancing the transport properties of conducting polymers by exploiting non-equilibrium states in the coupled system of electronic charges and counterions.

Self‐Doped Mixed Ionic‐Electronic Conductors to Tune the Threshold Voltage and the Mode of Operation in Organic Electrochemical Transistors

AbstractOrganic mixed ionic‐electronic conductors with tunable doping, low threshold voltages, and air stability are crucial for bioelectronic applications. A homopolymer based on an alkoxy thiophene monomer and its copolymer with a thiophene carrying ethylene glycol side chains are synthesized and converted to self‐doped conjugated polyelectrolytes, P3HOTS‐TMA+, and P3HOTS‐TMA+‐co‐P3MEEET. The self‐doping occurs during the conversion to polyelectrolytes. Both polyelectrolytes show high electrical conductivity without any external dopants. UV–Vis–NIR spectroscopy and spectroelectrochemistry confirm excellent air stability of the doped state. In an organic electrochemical transistor (OECT), the P3HOTS‐TMA+ operates in depletion mode, while P3HOTS‐TMA+‐co‐P3MEEET exhibits accumulation mode of operation with low threshold voltage, both showing fast response times. On the other hand, the non‐doped homopolymer, P3MEEET, shows a high negative threshold voltage in accumulation mode. Thus, copolymerization with the self‐dopable monomer changes the mode of operation as well as the threshold voltage substantially. Ultraviolet photoelectron spectroscopy reveals a considerable reduction of the hole injection barrier for the self‐doped system P3HOTS‐TMA+. Mott‐Schottky analysis shows reduction in charge carrier concentration in the copolymer compared to the homopolymer. Thus, the copolymerization strategy with a self‐dopable monomer is an efficient tool for tuning the degree of doping leading to low threshold voltage in OECTs.

Effects of Planarization of the Triphenylamine Unit on the Electronic and Transport Properties of Triarylamine-Fluorene Copolymers in Both Doped and Undoped Forms.

Triarylamine-alt-fluorene (TAF) copolymers are widely used for hole injection and transport in organic electronics. Despite suggestions to planarize the triphenylamine moiety, little research has been conducted. Here, we report a comprehensive investigation of the effects of planarization on the electronic and transport properties of a model TAF polymer semiconductor core. We compared the conventional twisted-propeller N-4-methoxyphenyl-N,N-diphenylamine-4',4″-diyl (TA) unit and its planarized bridged analogue (bTA) where adjacent o,o'-positions are linked by 1,1-dimethylmethylene. We studied both polyelectrolyte and non-polyelectrolyte forms of this core in both doped and undoped states. We found that planarization leads to an unprecedented trap-free transport of holes, and a pronounced enhancement of their mobility in the undoped state though less so in the doped state. Planarization also induces a slight reduction in the ionization energy of the undoped polymer, consequently lowering the work function of the doped polymer. This is accompanied by small spectral shifts: a red shift in the first absorption band of the undoped polymer and a blue shift in the first absorption band of the polaron. Furthermore, this study unveils new fundamental features of TAF polymers: (i) Doping induces the formation of three polaron bands within the subgap. (ii) Absorption of both neutral and polaron segments exhibit a linear intensity relationship with doping level. (iii) Electrical conductivity reaches a maximum at the half-doped state, varying as σ ∼ (x (1 - x))3 for 0.1 ≲ x ≲ 0.9, where x is the doping level. Finally, we demonstrate the successful integration of these self-compensated hole-doped TAF polymers as efficient hole injection layers in organic semiconductor diodes.

Twist angle-dependent transport properties of twisted bilayer graphene

Twisted bilayer graphene (tBLG) with small twist angles has attracted significant attention because of its unique electronic properties arising from the formation of a moiré superlattice. In this study, we systematically characterized the twist-angle-dependent electronic and transport properties of tBLG grown via chemical vapor deposition. This characterization included parameters such as the charge-neutral point voltage, carrier concentration, resistance, and mobility, covering a wide range of twist angles from 0° to 30°. We experimentally demonstrated that these parameters exhibited twist-angle-dependent moiré period trends, with high twist angles exceeding 9°, revealing more practically useful features, including improved mobilities compared to those of single-layer graphene. In addition, we demonstrated that the doping states and work functions were weakly dependent on the twist angles, as confirmed by additional first-principles calculations. This study provides valuable insights into the transport properties of tBLG and its potential for practical applications in the emerging field of twistronics.

Enhanced magnetic behavior of LaFeO3 by co-doping with Nd3+ and V5+ substitution (La0.8Nd0.2Fe0.95V0.05O3)

To enhance the quality of applications of LaFeO3 (LFO) as a magnetoelectric multiferroic through the improvement of magnetic behaviour, co-doping of Nd3+ (20 %) and V5+ (5 %) was considered for partial substitution in place of La3+ and Fe3+, respectively. Co-doped sample of La0.8Nd0.2Fe0.95V0.05O3 (LNFVO) was prepared by solid state reaction method. Rietveld analysis of X-ray diffractograms confirmed the formation as well as successful incorporation of dopants (Nd3+ and V5+) in La3+ and Fe3+ sites of the distorted perovskite structure with Pbnm space group. Morphological features including information related to crystallographic phase were examined by TEM. Distortion due to co-doping helped to achieve the stated objectives. Valence states of dopants and host cations were explored by analyzing XPS observations. Detailed magnetic measurements in the temperature range starting from 300 K down to 2 K suggested that magnetic property was drastically enhanced compared to that of the undoped, which was attributed to mismatch of valence states, ionic diameters etc. between dopants with host cations. The doped sample showed antiferromagnetic to ferromagnetic transition at and below 19 K. All such findings related to magnetic property would be quite attractive for the improvement of multiferroic applications as the low value of magnetization of pristine sample of LFO restrict it to become a good magnetoelectric multiferroic.