23 results found
Moser M, Hidalgo TC, Surgailis J, et al., 2020, Side Chain Redistribution as a Strategy to Boost Organic Electrochemical Transistor Performance and Stability, ADVANCED MATERIALS, ISSN: 0935-9648
Melianas A, Quill TJ, LeCroy G, et al., 2020, Temperature-resilient solid-state organic artificial synapses for neuromorphic computing, SCIENCE ADVANCES, Vol: 6, ISSN: 2375-2548
Giovannitti A, Rashid RB, Thiburce Q, et al., 2020, Energetic control of redox-active polymers toward safe organic Bioelectronic materials, Advanced Materials, Vol: 32, ISSN: 0935-9648
Avoiding faradaic side reactions during the operation of electrochemical devices is important to enhance the device stability, to achieve low power consumption, and to prevent the formation of reactive side‐products. This is particularly important for bioelectronic devices, which are designed to operate in biological systems. While redox‐active materials based on conducting and semiconducting polymers represent an exciting class of materials for bioelectronic devices, they are susceptible to electrochemical side‐reactions with molecular oxygen during device operation. Here, electrochemical side reactions with molecular oxygen are shown to occur during organic electrochemical transistor (OECT) operation using high‐performance, state‐of‐the‐art OECT materials. Depending on the choice of the active material, such reactions yield hydrogen peroxide (H2O2), a reactive side‐product, which may be harmful to the local biological environment and may also accelerate device degradation. A design strategy is reported for the development of redox‐active organic semiconductors based on donor–acceptor copolymers that prevents the formation of H2O2 during device operation. This study elucidates the previously overlooked side‐reactions between redox‐active conjugated polymers and molecular oxygen in electrochemical devices for bioelectronics, which is critical for the operation of electrolyte‐gated devices in application‐relevant environments.
Savva A, Hallani R, Cendra C, et al., 2020, Balancing Ionic and Electronic Conduction for High-Performance Organic Electrochemical Transistors, ADVANCED FUNCTIONAL MATERIALS, Vol: 30, ISSN: 1616-301X
Moser M, Thorley KJ, Moruzzi F, et al., 2019, Highly selective chromoionophores for ratiometric Na+ sensing based on an oligoethyleneglycol bridged bithiophene detection unit, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 7, Pages: 5359-5365, ISSN: 2050-7526
Moia D, Giovannitti A, Szumska AA, et al., 2019, Design and evaluation of conjugated polymers with polar side chains as electrode materials for electrochemical energy storage in aqueous electrolytes, Energy & Environmental Science, Vol: 12, Pages: 1349-1357, ISSN: 1754-5692
We report the development of redox-active conjugated polymers that have potential applications in electrochemical energy storage. Side chain engineering enables processing of the polymer electrodes from solution, stability in aqueous electrolytes and efficient transport of ionic and electronic charge carriers. We synthesized a 3,3′-dialkoxybithiophene homo-polymer (p-type polymer) with glycol side chains and prepared naphthalene-1,4,5,8-tetracarboxylic-diimide-dialkoxybithiophene (NDI-gT2) copolymers (n-type polymer) with either a glycol or zwitterionic side chain on the NDI unit. For the latter, we developed a post-functionalization synthesis to attach the polar zwitterion side chains to the polymer backbone to avoid challenges of purifying polar intermediates. We demonstrate fast and reversible charging of solution processed electrodes for both the p- and n-type polymers in aqueous electrolytes, without using additives or porous scaffolds and for films up to micrometers thick. We apply spectroelectrochemistry as an in operando technique to probe the state of charge of the electrodes. This reveals that thin films of the p-type polymer and zwitterion n-type polymer can be charged reversibly with up to two electronic charges per repeat unit (bipolaron formation). We combine thin films of these polymers in a two-electrode cell and demonstrate output voltages of up to 1.4 V with high redox-stability. Our findings demonstrate the potential of functionalizing conjugated polymers with appropriate polar side chains to improve the accessible capacity, and to improve reversibility and rate capabilities of polymer electrodes in aqueous electrolytes.
Kiefer D, Kroon R, Hofmann AI, et al., 2019, Double doping of conjugated polymers with monomer molecular dopants, NATURE MATERIALS, Vol: 18, Pages: 149-+, ISSN: 1476-1122
Cendra C, Giovannitti A, Savva A, et al., 2019, Role of the Anion on the Transport and Structure of Organic Mixed Conductors, ADVANCED FUNCTIONAL MATERIALS, Vol: 29, ISSN: 1616-301X
Moser M, Ponder JF, Wadsworth A, et al., 2018, Materials in Organic Electrochemical Transistors for Bioelectronic Applications: Past, Present, and Future, Advanced Functional Materials, ISSN: 1616-301X
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Organic electrochemical transistors are bioelectronic devices that exploit the coupled nature of ionic and electronic fluxes to achieve superior transducing abilities compared to conventional organic field effect transistors. In particular, the operation of organic electrochemical transistors relies on a channel material capable of conducting both ionic and electronic charge carriers to ensure bulk electrochemical doping. This review explores the various types of organic semiconductors that are employed as channel materials, with a particular focus on the past 5 years, during which the transducing abilities of organic electrochemical transistors have witnessed an almost tenfold increase. Specifically, the structure–property relationships of the various channel materials employed are investigated, highlighting how device performance can be related to functionality at the molecular level. Finally, an outlook on the field is provided, in particular toward the design guidelines of future materials and the challenges ahead in the field.
Venkatraman V, Friedlein JT, Giovannitti A, et al., 2018, Subthreshold operation of organic electrochemical transistors for biosignal amplification, Advanced Science, Vol: 5, ISSN: 2198-3844
With a host of new materials being investigated as active layers in organic electrochemical transistors (OECTs), several advantageous characteristics can be utilized to improve transduction and circuit level performance for biosensing applications. Here, the subthreshold region of operation of one recently reported high performing OECT material, poly(2‐(3,3′‐bis(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)‐[2,2′‐bithiophen]‐5‐yl)thieno[3,2‐b]thiophene), p(g2T‐TT) is investigated. The material's high subthreshold slope (SS) is exploited for high voltage gain and low power consumption. An ≈5× improvement in voltage gain (AV) for devices engineered for equal output current and 370× lower power consumption in the subthreshold region, in comparison to operation in the higher transconductance (g m), superthreshold region usually reported in the literature, are reported. Electrophysiological sensing is demonstrated using the subthreshold regime of p(g2T‐TT) devices and it is suggested that operation in this regime enables low power, enhanced sensing for a broad range of bioelectronic applications. Finally, the accessibility of the subthreshold regime of p(g2T‐TT) is evaluated in comparison with the prototypical poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and the role of material design in achieving favorable properties for subthreshold operation is discussed.
Pappa A-M, Ohayon D, Giovannitti A, et al., 2018, Direct metabolite detection with an n-type accumulation mode organic electrochemical transistor, Science Advances, Vol: 4, ISSN: 2375-2548
The inherent specificity and electrochemical reversibility of enzymes poise them as the biorecognition element of choice for a wide range of metabolites. To use enzymes efficiently in biosensors, the redox centers of the protein should have good electrical communication with the transducing electrode, which requires either the use of mediators or tedious biofunctionalization approaches. We report an all-polymer micrometer-scale transistor platform for the detection of lactate, a significant metabolite in cellular metabolic pathways associated with critical health care conditions. The device embodies a new concept in metabolite sensing where we take advantage of the ion-to-electron transducing qualities of an electron-transporting (n-type) organic semiconductor and the inherent amplification properties of an ion-to-electron converting device, the organic electrochemical transistor. The n-type polymer incorporates hydrophilic side chains to enhance ion transport/injection, as well as to facilitate enzyme conjugation. The material is capable of accepting electrons of the enzymatic reaction and acts as a series of redox centers capable of switching between the neutral and reduced state. The result is a fast, selective, and sensitive metabolite sensor. The advantage of this device compared to traditional amperometric sensors is the amplification of the input signal endowed by the electrochemical transistor circuit and the design simplicity obviating the need for a reference electrode. The combination of redox enzymes and electron-transporting polymers will open up an avenue not only for the field of biosensors but also for the development of enzyme-based electrocatalytic energy generation/storage devices.
Zhang Y, Wustoni S, Savva A, et al., 2018, Lipid bilayer formation on organic electronic materials, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 6, Pages: 5218-5227, ISSN: 2050-7526
Giovannitti A, Thorley K, Nielsen C, et al., 2018, Redox-stability of alkoxy-BDT copolymers and their use for organic bioelectronic devices, Advanced Functional Materials, Vol: 28, ISSN: 1616-301X
Organic semiconductors can be employed as the active layer in accumulation mode organic electrochemical transistors (OECTs), where redox stability in aqueous electrolytes is important for long‐term recordings of biological events. It is observed that alkoxy‐benzo[1,2‐b:4,5‐b′]dithiophene (BDT) copolymers can be extremely unstable when they are oxidized in aqueous solutions. The redox stability of these copolymers can be improved by molecular design of the copolymer where it is observed that the electron rich comonomer 3,3′‐dimethoxy‐2,2′‐bithiophene (MeOT2) lowers the oxidation potential and also stabilizes positive charges through delocalization and resonance effects. For copolymers where the comonomers do not have the same ability to stabilize positive charges, irreversible redox reactions are observed with the formation of quinone structures, being detrimental to performance of the materials in OECTs. Charge distribution along the copolymer from density functional theory calculations is seen to be an important factor in the stability of the charged copolymer. As a result of the stabilizing effect of the comonomer, a highly stable OECT performance is observed with transconductances in the mS range. The analysis of the decomposition pathway also raises questions about the general stability of the alkoxy‐BDT unit, which is heavily used in donor–acceptor copolymers in the field of photovoltaics.
Giovannitti A, Maria I, Hanifi D, et al., 2018, The role of the side chain on the performance of n-type conjugated polymers in aqueous electrolytes, Chemistry of Materials, Vol: 30, Pages: 2945-2953, ISSN: 0897-4756
We report a design strategy that allows the preparation of solution processable n type materials from low boiling point solvents for organic electrochemical transistors (OECTs). The polymer backbone is based on NDI-T2 copolymers where a branched alkyl side chain is gradually exchanged for a linear ethylene glycol based side chain. A series of random copolymers are prepared with glycol side chain percentages of 0, 10, 25, 50, 75, 90 and 100 with respect to the alkyl side chains. These are characterized in order to study the influence of the polar side chains on interaction with aqueous electrolytes, their electrochemical redox reactions and performance in OECTs when operated in aqueous electrolytes. We observe that glycol side chain percentages of >50 % are required to achieve volumetric charging while lower glycol chain percentages show a mixed operation with high required voltages to allow for bulk charging of the organic semiconductor. A strong dependence of the electron mobility on the fraction of glycol chains was found for copolymers based on NDI-T2, with a significant drop as alkyl side chains are replaced by glycol side chains.
Kiefer D, Giovannitti A, Sun H, et al., 2018, Enhanced n-Doping Efficiency of a Naphthalenediimide-Based Copolymer through Polar Side Chains for Organic Thermoelectrics, ACS ENERGY LETTERS, Vol: 3, Pages: 278-285, ISSN: 2380-8195
Kiefer D, Giovannitti A, Sun H, et al., 2018, Enhanced n-Doping Efficiency of a Naphthalenediimide-Based Copolymer through Polar Side Chains for Organic Thermoelectrics., ACS Energy Lett, Vol: 3, Pages: 278-285, ISSN: 2380-8195
N-doping of conjugated polymers either requires a high dopant fraction or yields a low electrical conductivity because of their poor compatibility with molecular dopants. We explore n-doping of the polar naphthalenediimide-bithiophene copolymer p(gNDI-gT2) that carries oligoethylene glycol-based side chains and show that the polymer displays superior miscibility with the benzimidazole-dimethylbenzenamine-based n-dopant N-DMBI. The good compatibility of p(gNDI-gT2) and N-DMBI results in a relatively high doping efficiency of 13% for n-dopants, which leads to a high electrical conductivity of more than 10-1 S cm-1 for a dopant concentration of only 10 mol % when measured in an inert atmosphere. We find that the doped polymer is able to maintain its electrical conductivity for about 20 min when exposed to air and recovers rapidly when returned to a nitrogen atmosphere. Overall, solution coprocessing of p(gNDI-gT2) and N-DMBI results in a larger thermoelectric power factor of up to 0.4 μW K-2 m-1 compared to other NDI-based polymers.
Zhang Y, Li J, Li R, et al., 2017, Liquid-Solid Dual-Gate Organic Transistors with Tunable Threshold Voltage for Cell Sensing, ACS APPLIED MATERIALS & INTERFACES, Vol: 9, Pages: 38687-38694, ISSN: 1944-8244
Giovannitti A, Nielsen CB, Sbircea DT, et al., 2016, Erratum: N-type organic electrochemical transistors with stability in water., Nat Commun, Vol: 7, Pages: 13955-13955
Giovannitti A, Sbircea DTS, Inal SI, et al., 2016, Controlling the mode of operation of organic transistors through side chain engineering, Proceedings of the National Academy of Sciences of the United States of America, Vol: 143, Pages: 12017-12022, ISSN: 1091-6490
Electrolyte-gated organic transistors offer low bias operation facilitated by direct contact of the transistor channel with an electrolyte. Their operation mode is generally defined by the dimensionality of charge transport, where a field-effect transistor allows for electrostatic charge accumulation at the electrolyte/semiconductor interface, whereas an organic electrochemical transistor (OECT) facilitates penetration of ions into the bulk of the channel, considered a slow process, leading to volumetric doping and electronic transport. Conducting polymer OECTs allow for fast switching and high currents through incorporation of excess, hygroscopic ionic phases, but operate in depletion mode. Here, we show that the use of glycolated side chains on a thiophene backbone can result in accumulation mode OECTs with high currents, transconductance, and sharp subthreshold switching, while maintaining fast switching speeds. Compared with alkylated analogs of the same backbone, the triethylene glycol side chains shift the mode of operation of aqueous electrolyte-gated transistors from interfacial to bulk doping/transport and show complete and reversible electrochromism and high volumetric capacitance at low operating biases. We propose that the glycol side chains facilitate hydration and ion penetration, without compromising electronic mobility, and suggest that this synthetic approach can be used to guide the design of organic mixed conductors.
Giovannitti A, nielsen CN, Sbircea DTS, et al., 2016, N-type organic electrochemical transistors with stability in water, Nature Communications, Vol: 7, ISSN: 2041-1723
Organic electrochemical transistors (OECTs) are receiving significant attention due to their ability to efficiently transduce biological signals. A major limitation of this technology is that only p-type materials have been reported, which precludes the development of complementary circuits, and limits sensor technologies. Here, we report the first ever n-type OECT, with relatively balanced ambipolar charge transport characteristics based on a polymer that supports both hole and electron transport along its backbone when doped through an aqueous electrolyte and in the presence of oxygen. This new semiconducting polymer is designed specifically to facilitate ion transport and promote electrochemical doping. Stability measurements in water show no degradation when tested for 2 h under continuous cycling. This demonstration opens the possibility to develop complementary circuits based on OECTs and to improve the sophistication of bioelectronic devices.
Nielsen CBN, Giovannitti A, Sbircea DTS, et al., 2016, Molecular Design of Semiconducting Polymers for High-Performance Organic Electrochemical Transistors, Journal of the American Chemical Society, Vol: 138, Pages: 10252-10259, ISSN: 1520-5126
The organic electrochemical transistor (OECT), capable of transducing small ionic fluxes into electronic signals in anaqueous environment, is an ideal device to utilize in bioelectronic applications. Currently, most OECTs are fabricated with commerciallyavailable conducting poly(3,4-ethylenedioxythiophene) (PEDOT)-based suspensions and are therefore operated in depletionmode. Here, we present a series of semiconducting polymers designed to elucidate important structure-property guidelines requiredfor accumulation mode OECT operation. We discuss key aspects relating to OECT performance such as ion and hole transport,electrochromic properties, operational voltage and stability. The demonstration of our molecular design strategy is the fabrication ofaccumulation mode OECTs that clearly outperform state-of-the-art PEDOT based devices, and show stability under aqueous operationwithout the need for formulation additives and cross-linkers.
Giovannitti A, McCulloch I, Nielsen C, et al., 2015, Sodium and potassium ion selective conjugated polymers for optical ion detection in solution and solid state, Advanced Functional Materials, Vol: 26, Pages: 514-523, ISSN: 1616-3028
This paper presents the development of alkali metal ion selective small molecules and conjugated polymers for optical ion sensing. A crown ether bithiophene unit was chosen as the detecting unit, as both a small molecule and incorporated into a conjugated aromatic structure. The complex formation and the resulting backbone twist of the detector unit was investigated by UV Vis and NMR spectroscopy where a remarkable selectivity towards sodium or potassium ions was found. X-Ray diffraction analysis of single crystals with and without alkali metal ions was carried out and a difference of the dihedral angle of more than 70 ° was observed. In a conjugated polymer structure, the detector unit has a higher sensitivity for alkali metal ion detection than its small molecule analogue. Ion selectivity was retained in polymers with solubility in polar solvents facilitated by the attachment of polar ethylene glycol side chains. This design concept was further evolved to develop a sodium-salt solid state sensor based on blends of the detecting polymer with a polyvinyl alcohol matrix where the detection of sodium ions was achieved in aqueous salt solutions with concentrations similar to biological important environments.
Giovannitti A, Seifermann SM, Bihlmeier A, et al., 2013, Single and Multiple Additions of Dibenzoylmethane onto Buckminsterfullerene, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Vol: 2013, Pages: 7907-7913, ISSN: 1434-193X
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