Alexander Giovannitti

All Publications

• Impact of Side Chain Hydrophilicity on Packing, Swelling and Ion Interactions in Oxy-bithiophene Semiconductors. Advanced materials (Deerfield Beach, Fla.) Siemons, N., Pearce, D., Cendra, C., Yu, H., Tuladhar, S. M., Hallani, R. K., Sheelamanthula, R., LeCroy, G. S., Siemons, L., White, A. J., Mcculloch, I., Salleo, A., Frost, J. M., Giovannitti, A., Nelson, J. 2022: e2204258

  Abstract

  Exchanging hydrophobic alkyl-based side chains to hydrophilic glycol-based side chains is a widely adopted method for improving mixed-transport device performance, despite the impact on solid state packing and polymer-electrolyte interactions being poorly understood. Presented here is a Molecular Dynamics (MD) force field for modelling alkoxylated and glycolated polythiophenes. The force field is validated against known packing motifs for their monomer crystals. MD simulations, coupled with X-ray Diffraction (XRD), show that alkoxylated polythiophenes will pack with a 'tilted stack' and straight interdigitating side chains, whilst their glycolated counterpart will pack with a 'deflected stack' and an s-bend side chain configuration. MD simulations reveal water penetration pathways into the alkoxylated and glycolated crystals - through the pi-stack and through the lamellar stack respectively. Finally, the two distinct ways tri-ethylene glycol polymers can bind to cations are revealed, showing the formation of a meta-stable single bound state, or an energetically deep double bound state, both with a strong side chain length dependance. The minimum energy pathways for the formation of the chelates are identified, showing the physical process through which cations can bind to one or two side chains of a glycolated polythiophene, with consequences for ion transport in bithiophene semiconductors. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202204258

  View details for PubMedID 35946142

• Redox-Active Polymers Designed for the Circular Economy of Energy Storage Devices ACS ENERGY LETTERS Tan, S., Quill, T. J., Moser, M., LeCroy, G., Chen, X., Wu, Y., Takacs, C. J., Salleo, A., Giovannitti, A. 2021; 6 (10): 3450-3457

  View details for DOI 10.1021/acsenergylett.1c01625

  View details for Web of Science ID 000707987500008

• High-Gain Chemically Gated Organic Electrochemical Transistor ADVANCED FUNCTIONAL MATERIALS Tan, S., Giovannitti, A., Melianas, A., Moser, M., Cotts, B. L., Singh, D., McCulloch, I., Salleo, A. 2021

  View details for DOI 10.1002/adfm.202010868

  View details for Web of Science ID 000624582200001

• Reversible Electrochemical Charging of n-Type Conjugated Polymer Electrodes in Aqueous Electrolytes. Journal of the American Chemical Society Szumska, A. A., Maria, I. P., Flagg, L. Q., Savva, A., Surgailis, J., Paulsen, B. D., Moia, D., Chen, X., Griggs, S., Mefford, J. T., Rashid, R. B., Marks, A., Inal, S., Ginger, D. S., Giovannitti, A., Nelson, J. 2021

  Abstract

  Conjugated polymers achieve redox activity in electrochemical devices by combining redox-active, electronically conducting backbones with ion-transporting side chains that can be tuned for different electrolytes. In aqueous electrolytes, redox activity can be accomplished by attaching hydrophilic side chains to the polymer backbone, which enables ionic transport and allows volumetric charging of polymer electrodes. While this approach has been beneficial for achieving fast electrochemical charging in aqueous solutions, little is known about the relationship between water uptake by the polymers during electrochemical charging and the stability and redox potentials of the electrodes, particularly for electron-transporting conjugated polymers. We find that excessive water uptake during the electrochemical charging of polymer electrodes harms the reversibility of electrochemical processes and results in irreversible swelling of the polymer. We show that small changes of the side chain composition can significantly increase the reversibility of the redox behavior of the materials in aqueous electrolytes, improving the capacity of the polymer by more than one order of magnitude. Finally, we show that tuning the local environment of the redox-active polymer by attaching hydrophilic side chains can help to reach high fractions of the theoretical capacity for single-phase electrodes in aqueous electrolytes. Our work shows the importance of chemical design strategies for achieving high electrochemical stability for conjugated polymers in aqueous electrolytes.

  View details for DOI 10.1021/jacs.1c06713

  View details for PubMedID 34469688

• Energetic Control of Redox-Active Polymers toward Safe Organic Bioelectronic Materials. Advanced materials (Deerfield Beach, Fla.) Giovannitti, A., Rashid, R. B., Thiburce, Q., Paulsen, B. D., Cendra, C., Thorley, K., Moia, D., Mefford, J. T., Hanifi, D., Weiyuan, D., Moser, M., Salleo, A., Nelson, J., McCulloch, I., Rivnay, J. 2020: e1908047

  Abstract

  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 (H2 O2 ), 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 H2 O2 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.

  View details for DOI 10.1002/adma.201908047

  View details for PubMedID 32125736

• Design and evaluation of conjugated polymers with polar side chains as electrode materials for electrochemical energy storage in aqueous electrolytes ENERGY & ENVIRONMENTAL SCIENCE Moia, D., Giovannitti, A., Szumska, A. A., Maria, I. P., Rezasoltani, E., Sachs, M., Schnurr, M., Barnes, P. F., McCulloch, I., Nelson, J. 2019; 12 (4): 1349–57

  View details for DOI 10.1039/c8ee03518k

  View details for Web of Science ID 000465275800015

• The Role of the Side Chain on the Performance of N-type Conjugated Polymers in Aqueous Electrolytes CHEMISTRY OF MATERIALS Giovannitti, A., Maria, I. P., Hanifi, D., Donahue, M. J., Bryant, D., Barth, K. J., Makdah, B. E., Savva, A., Moia, D., Zetek, M., Barnes, P. F., Reid, O. G., Inal, S., Rumbles, G., Malliaras, G. G., Nelson, J., Rivnay, J., McCulloch, I. 2018; 39 (9): 2945–53

  Abstract

  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 was prepared with glycol side chain percentages of 0, 10, 25, 50, 75, 90, and 100 with respect to the alkyl side chains. These were characterized 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 observed 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.

  View details for PubMedID 29780208

  View details for PubMedCentralID PMC5953566

• Redox-Stability of Alkoxy-BDT Copolymers and their Use for Organic Bioelectronic Devices ADVANCED FUNCTIONAL MATERIALS Giovannitti, A., Thorley, K. J., Nielsen, C. B., Li, J., Donahue, M. J., Malliaras, G. G., Rivnay, J., McCulloch, I. 2018; 28 (17)

  View details for DOI 10.1002/adfm.201706325

  View details for Web of Science ID 000430658300008

• 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 Giovannitti, A., Sbircea, D., Inal, S., Nielsen, C. B., Bandiello, E., Hanifi, D. A., Sessolo, M., Malliaras, G. G., McCulloch, I., Rivnay, J. 2016; 113 (43): 12017-12022

  Abstract

  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.

  View details for PubMedID 27790983

• N-type organic electrochemical transistors with stability in water NATURE COMMUNICATIONS Giovannitti, A., Nielsen, C. B., Sbircea, D., Inal, S., Donahue, M., Niazi, M. R., Hanifi, D. A., Amassian, A., Malliaras, G. G., Rivnay, J., McCulloch, I. 2016; 7

  Abstract

  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.

  View details for DOI 10.1038/ncomms13066

  View details for Web of Science ID 000385587100001

  View details for PubMedID 27713414

  View details for PubMedCentralID PMC5059848

• Molecular Design of Semiconducting Polymers for High-Performance Organic Electrochemical Transistors. Journal of the American Chemical Society Nielsen, C. B., Giovannitti, A., Sbircea, D., Bandiello, E., Niazi, M. R., Hanifi, D. A., Sessolo, M., Amassian, A., Malliaras, G. G., Rivnay, J., McCulloch, I. 2016; 138 (32): 10252-10259

  Abstract

  The organic electrochemical transistor (OECT), capable of transducing small ionic fluxes into electronic signals in an aqueous environment, is an ideal device to utilize in bioelectronic applications. Currently, most OECTs are fabricated with commercially available conducting poly(3,4-ethylenedioxythiophene) (PEDOT)-based suspensions and are therefore operated in depletion mode. Here, we present a series of semiconducting polymers designed to elucidate important structure-property guidelines required for 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 of accumulation mode OECTs that clearly outperform state-of-the-art PEDOT-based devices, and show stability under aqueous operation without the need for formulation additives and cross-linkers.

  View details for DOI 10.1021/jacs.6b05280

  View details for PubMedID 27444189

  View details for PubMedCentralID PMC4991841

• Enhancing the Backbone Coplanarity of n-Type Copolymers for Higher Electron Mobility and Stability in Organic Electrochemical Transistors. Chemistry of materials : a publication of the American Chemical Society Maria, I. P., Griggs, S., Rashid, R. B., Paulsen, B. D., Surgailis, J., Thorley, K., Le, V. N., Harrison, G. T., Combe, C., Hallani, R., Giovannitti, A., Paterson, A. F., Inal, S., Rivnay, J., McCulloch, I. 2022; 34 (19): 8593-8602

  Abstract

  Electron-transporting (n-type) conjugated polymers have recently been applied in numerous electrochemical applications, where both ion and electron transport are required. Despite continuous efforts to improve their performance and stability, n-type conjugated polymers with mixed conduction still lag behind their hole-transporting (p-type) counterparts, limiting the functions of electrochemical devices. In this work, we investigate the effect of enhanced backbone coplanarity on the electrochemical activity and mixed ionic-electronic conduction properties of n-type polymers during operation in aqueous media. Through substitution of the widely employed electron-deficient naphthalene diimide (NDI) unit for the core-extended naphthodithiophene diimide (NDTI) units, the resulting polymer shows a more planar backbone with closer packing, leading to an increase in the electron mobility in organic electrochemical transistors (OECTs) by more than two orders of magnitude. The NDTI-based polymer shows a deep-lying lowest unoccupied molecular orbital level, enabling operation of the OECT closer to 0 V vs Ag/AgCl, where fewer parasitic reactions with molecular oxygen occur. Enhancing the backbone coplanarity also leads to a lower affinity toward water uptake during cycling, resulting in improved stability during continuous electrochemical charging and ON-OFF switching relative to the NDI derivative. Furthermore, the NDTI-based polymer also demonstrates near-perfect shelf-life stability over a month-long test, exhibiting a negligible decrease in both the maximum on-current and transconductance. Our results highlight the importance of polymer backbone design for developing stable, high-performing n-type materials with mixed ionic-electronic conduction in aqueous media.

  View details for DOI 10.1021/acs.chemmater.2c01552

  View details for PubMedID 36248228

  View details for PubMedCentralID PMC9558307

• Conjugated polymers for microwave applications: untethered sensing platforms and multifunctional devices. Advanced materials (Deerfield Beach, Fla.) Tan, S. T., Giovannitti, A., Marks, A., Moser, M., Quill, T. J., McCulloch, I., Salleo, A., Bonacchini, G. E. 2022: e2202994

  Abstract

  In the past two decades, organic electronic materials have enabled and accelerated a large and diverse set of technologies, from energy harvesting devices and electro-mechanical actuators, to flexible and printed (opto)electronic circuitry. Among organic (semi)conductors, mixed ionic-electron conductors (OMIECs) are now at the center of renewed interest in organic electronics, as they are key drivers of recent developments in the fields of bioelectronics, energy storage, and neuromorphic computing. However, due to the relatively slow switching dynamics of organic electronics, their application in microwave technology, until recently, has been overlooked. Nonetheless, other unique properties of OMIECs, such as their substantial electrochemical tunability, charge modulation range and processability, make this field of use ripe with opportunities. In this work, we demonstrate the use of a series of solution-processed intrinsic OMIECs to actively tune the properties of metamaterial-inspired microwave devices, including an untethered bioelectrochemical sensing platform that requires no external power, and a tunable resonating structure with independent amplitude- and frequency-modulation. These devices showcase the considerable potential of OMIEC-based metadevices in autonomous bioelectronics and reconfigurable microwave optics. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202202994

  View details for PubMedID 35759573

• Tuning Organic Electrochemical Transistor Threshold Voltage using Chemically Doped Polymer Gates. Advanced materials (Deerfield Beach, Fla.) Tan, S. T., Lee, G., Denti, I., LeCroy, G., Rozylowicz, K., Marks, A., Griggs, S., McCulloch, I., Giovannitti, A., Salleo, A. 2022: e2202359

  Abstract

  Organic electrochemical transistors (OECTs) have shown promise as transducers and amplifiers of minute electronic potentials due to their large transconductances. Tuning OECT threshold voltage is important to achieve low-powered devices with amplification properties within the desired operational voltage range. However, traditional design approaches have struggled to decouple channel and materials properties from threshold voltage, thereby compromising on several other OECT performance metrics such as electrochemical stability, transconductance, and dynamic range. In this work, we utilize simple solution processing methods to chemically dope polymer gate electrodes, thereby controlling their work function, which in turn tunes the operation voltage range of OECTs without perturbing their channel properties. Chemical doping of initially air-sensitive polymer electrodes further improves their electrochemical stability in ambient conditions. Thus, we demonstrate, for the first time, OECTs which are simultaneously low-powered and electrochemically resistant to oxidative side reactions at ambient conditions. This approach shows that threshold voltage, which was once interwoven with other OECT properties, can in fact be an independent design parameter, expanding the design space of OECTs. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202202359

  View details for PubMedID 35737653

• Efficient Electronic Tunneling Governs Transport in Conducting Polymer-Insulator Blends. Journal of the American Chemical Society Keene, S. T., Michaels, W., Melianas, A., Quill, T. J., Fuller, E. J., Giovannitti, A., McCulloch, I., Talin, A. A., Tassone, C. J., Qin, J., Troisi, A., Salleo, A. 2022

  Abstract

  Electronic transport models for conducting polymers (CPs) and blends focus on the arrangement of conjugated chains, while the contributions of the nominally insulating components to transport are largely ignored. In this work, an archetypal CP blend is used to demonstrate that the chemical structure of the non-conductive component has a substantial effect on charge carrier mobility. Upon diluting a CP with excess insulator, blends with as high as 97.4 wt % insulator can display carrier mobilities comparable to some pure CPs such as polyaniline and low regioregularity P3HT. In this work, we develop a single, multiscale transport model based on the microstructure of the CP blends, which describes the transport properties for all dilutions tested. The results show that the high carrier mobility of primarily insulator blends results from the inclusion of aromatic rings, which facilitate long-range tunneling (up to ca. 3 nm) between isolated CP chains. This tunneling mechanism calls into question the current paradigm used to design CPs, where the solubilizing or ionically conducting component is considered electronically inert. Indeed, optimizing the participation of the nominally insulating component in electronic transport may lead to enhanced electronic mobility and overall better performance in CPs.

  View details for DOI 10.1021/jacs.2c02139

  View details for PubMedID 35658455

• Critical analysis of self-doping and water-soluble n-type organic semiconductors: structures and mechanisms JOURNAL OF MATERIALS CHEMISTRY C Cowen, L. M., Gilhooly-Finn, P. A., Giovannitti, A., LeCroy, G., Demetriou, H., Neal, W., Dong, Y., Westwood, M., Luong, S., Fenwick, O., Salleo, A., Heutz, S., Nielsen, C. B., Schroeder, B. C. 2022

  View details for DOI 10.1039/d2tc01108e

  View details for Web of Science ID 000801023700001

• Organic neuromorphic electronics for sensorimotor integration and learning in robotics. Science advances Krauhausen, I., Koutsouras, D. A., Melianas, A., Keene, S. T., Lieberth, K., Ledanseur, H., Sheelamanthula, R., Giovannitti, A., Torricelli, F., Mcculloch, I., Blom, P. W., Salleo, A., van de Burgt, Y., Gkoupidenis, P. 2021; 7 (50): eabl5068

  Abstract

  [Figure: see text].

  View details for DOI 10.1126/sciadv.abl5068

  View details for PubMedID 34890232

• Electrochemistry of Thin Films with In Situ/Operando Grazing Incidence X-Ray Scattering: Bypassing Electrolyte Scattering for High Fidelity Time Resolved Studies. Small (Weinheim an der Bergstrasse, Germany) Paulsen, B. D., Giovannitti, A., Wu, R., Strzalka, J., Zhang, Q., Rivnay, J., Takacs, C. J. 2021: e2103213

  Abstract

  Electroactive polymer thin films undergo repeated reversible structural change during operation in electrochemical applications. While synchrotron X-ray scattering is powerful for the characterization of stand-alone and ex situ organic thin films, in situ/operando structural characterization has been underutilized-in large part due to complications arising from supporting electrolyte scattering. This has greatly hampered the development of application relevant structure property relationships. Therefore, a new methodology for in situ/operando X-ray characterization that separates the incident and scattered X-ray beam path from the electrolyte is developed. As a proof of concept, the operando structural characterization of weakly-scattering, organic mixed conducting thin films in an aqueous electrolyte environment is demonstrated, accessing previously unexplored changes in the pi-pi peak and diffuse scatter, while capturing the solvent swollen thin film structure which is inaccessible in previous ex situ studies. These in situ/operando measurements improve the sensitivity to structural changes, capturing minute changes not possible ex situ, and have multimodal potential such as combined Raman measurements that also serve to validate the true in situ/operando conditions of the cell. Finally, new directions enabled by this in situ/operando cell design are examined and state of the art measurements are compared.

  View details for DOI 10.1002/smll.202103213

  View details for PubMedID 34549509

• Operation mechanism of organic electrochemical transistors as redox chemical transducers JOURNAL OF MATERIALS CHEMISTRY C Tan, S., Keene, S., Giovannitti, A., Melianas, A., Moser, M., McCulloch, I., Salleo, A. 2021

  View details for DOI 10.1039/d1tc02224e

  View details for Web of Science ID 000681616700001

• The Effect of Alkyl Spacers on the Mixed Ionic-Electronic Conduction Properties of N-Type Polymers ADVANCED FUNCTIONAL MATERIALS Maria, I. P., Paulsen, B. D., Savva, A., Ohayon, D., Wu, R., Hallani, R., Basu, A., Du, W., Anthopoulos, T. D., Inal, S., Rivnay, J., McCulloch, I., Giovannitti, A. 2021

  View details for DOI 10.1002/adfm.202008718

  View details for Web of Science ID 000608924800001

• Side Chain Redistribution as a Strategy to Boost Organic Electrochemical Transistor Performance and Stability. Advanced materials (Deerfield Beach, Fla.) Moser, M., Hidalgo, T. C., Surgailis, J., Gladisch, J., Ghosh, S., Sheelamanthula, R., Thiburce, Q., Giovannitti, A., Salleo, A., Gasparini, N., Wadsworth, A., Zozoulenko, I., Berggren, M., Stavrinidou, E., Inal, S., McCulloch, I. 2020: e2002748

  Abstract

  A series of glycolated polythiophenes for use in organic electrochemical transistors (OECTs) is designed and synthesized, differing in the distribution of their ethylene glycol chains that are tethered to the conjugated backbone. While side chain redistribution does not have a significant impact on the optoelectronic properties of the polymers, this molecular engineering strategy strongly impacts the water uptake achieved in the polymers. By careful optimization of the water uptake in the polymer films, OECTs with unprecedented steady-state performances in terms of [muC* ] and current retentions up to 98% over 700 electrochemical switching cycles are developed.

  View details for DOI 10.1002/adma.202002748

  View details for PubMedID 32754923

• Temperature-resilient solid-state organic artificial synapses for neuromorphic computing SCIENCE ADVANCES Melianas, A., Quill, T. J., LeCroy, G., Tuchman, Y., v Loo, H., Keene, S. T., Giovannitti, A., Lee, H. R., Maria, I. P., McCulloch, Salleo, A. 2020; 6 (27)

  View details for DOI 10.1126/sciadv.abb2958

  View details for Web of Science ID 000548735500035

• Balancing Ionic and Electronic Conduction for High-Performance Organic Electrochemical Transistors ADVANCED FUNCTIONAL MATERIALS Savva, A., Hallani, R., Cendra, C., Surgailis, J., Hidalgo, T. C., Wustoni, S., Sheelamanthula, R., Chen, X., Kirkus, M., Giovannitti, A., Salleo, A., McCulloch, I., Inal, S. 2020

  View details for DOI 10.1002/adfm.201907657

  View details for Web of Science ID 000509617300001

• Polaron Delocalization in Donor-Acceptor Polymers and its Impact on Organic Electrochemical Transistor Performance. Angewandte Chemie (International ed. in English) Moser, M. n., Savva, A. n., Thorley, K. n., Paulsen, B. D., Hidalgo, T. C., Ohayon, D. n., Chen, H. n., Giovannitti, A. n., Marks, A. n., Gasparini, N. n., Wadsworth, A. n., Rivnay, J. n., Inal, S. n., McCulloch, I. n. 2020

  Abstract

  Donor-acceptor (D-A) polymers are promising materials for organic electrochemical transistors (OECTs), as they minimize detrimental faradaic side-reactions during OECT operation, yet their steady-state OECT performance still lags far behind their all-donor counterparts. Here, we report three D-A polymers based on the diketopyrrolopyrrole unit that afford OECT performances similar to those of all-donor polymers, hence representing a significant improvement to the previously developed D-A copolymers. In addition to improved OECT performance, DFT simulations of the polymers and their respective hole polarons also revealed a positive correlation between hole polaron delocalization and steady-state OECT performance, providing new insights into the design of OECT materials. More importantly, we demonstrate how polaron delocalization can be tuned directly at the molecular level by selection of the building blocks comprising the polymers' conjugated backbone, thus paving the way for the development of even higher performing OECT polymers.

  View details for DOI 10.1002/anie.202014078

  View details for PubMedID 33259685

• Reversible Electronic Solid-Gel Switching of a Conjugated Polymer ADVANCED SCIENCE Gladisch, J., Stavrinidou, E., Ghosh, S., Giovannitti, A., Moser, M., Zozoulenko, I., McCulloch, I., Berggren, M. 2020; 7 (2): 1901144

  Abstract

  Conjugated polymers exhibit electrically driven volume changes when included in electrochemical devices via the exchange of ions and solvent. So far, this volumetric change is limited to 40% and 100% for reversible and irreversible systems, respectively, thus restricting potential applications of this technology. A conjugated polymer that reversibly expands by about 300% upon addressing, relative to its previous contracted state, while the first irreversible actuation can achieve values ranging from 1000-10 000%, depending on the voltage applied is reported. From experimental and theoretical studies, it is found that this large and reversible volumetric switching is due to reorganization of the polymer during swelling as it transforms between a solid-state phase and a gel, while maintaining percolation for conductivity. The polymer is utilized as an electroactive cladding to reduce the void sizes of a porous carbon filter electrode by 85%.

  View details for DOI 10.1002/advs.201901144

  View details for Web of Science ID 000492740700001

  View details for PubMedID 31993279

  View details for PubMedCentralID PMC6974956

• Highly selective chromoionophores for ratiometric Na+ sensing based on an oligoethyleneglycol bridged bithiophene detection unit JOURNAL OF MATERIALS CHEMISTRY C Moser, M., Thorley, K. J., Moruzzi, F., Ponder, J. F., Maria, I. P., Giovannitti, A., Inal, S., McCulloch, I. 2019; 7 (18): 5359–65

  View details for DOI 10.1039/c8tc06000b

  View details for Web of Science ID 000472443000018

• Materials in Organic Electrochemical Transistors for Bioelectronic Applications: Past, Present, and Future ADVANCED FUNCTIONAL MATERIALS Moser, M., Ponder, J. F., Wadsworth, A., Giovannitti, A., McCulloch, I. 2019; 29 (21)

  View details for DOI 10.1002/adfm.201807033

  View details for Web of Science ID 000473101200002

• Nanoscale Ion-Doped Polymer Transistors NANO LETTERS Thiburce, Q., Giovannitti, A., McCulloch, I., Campbell, A. J. 2019; 19 (3): 1712–18

  View details for DOI 10.1021/acs.nanolett.8b04717

  View details for Web of Science ID 000461537600039

• Nanoscale Ion-Doped Polymer Transistors. Nano letters Thiburce, Q., Giovannitti, A., McCulloch, I., Campbell, A. J. 2019

  Abstract

  Organic transistors with submicron dimensions have been shown to deviate from the expected behavior due to a variety of so-called "short-channel" effects, resulting in nonlinear output characteristics and a lack of current saturation, considerably limiting their use. Using an electrochemically doped polymer in which ions are dynamically injected and removed from the bulk of the semiconductor, we show that devices with nanoscale channel lengths down to 50 nm exhibit output curves with well-defined linear and saturation regimes. Additionally, they show very large on-currents on par with their microscale counterparts, large on-to-off ratios of 108, and record-high width-normalized transconductances above 10 S m-1. We believe this work paves the way for the fabrication of high-gain, high-current polymer integrated circuits such as sensor arrays operating at voltages below |1 V| and prepared using simple solution-processing methods.

  View details for PubMedID 30720280

• Influence of Water on the Performance of Organic Electrochemical Transistors CHEMISTRY OF MATERIALS Savva, A., Cendra, C., Giugni, A., Torre, B., Surgailis, J., Ohayon, D., Giovannitti, A., McCulloch, I., Di Fabrizio, E., Salleo, A., Rivnay, J., Inal, S. 2019; 31 (3): 927–37

  View details for DOI 10.1021/acs.chemmater.8b04335

  View details for Web of Science ID 000458937800034

• Role of the Anion on the Transport and Structure of Organic Mixed Conductors ADVANCED FUNCTIONAL MATERIALS Cendra, C., Giovannitti, A., Savva, A., Venkatraman, V., McCulloch, I., Salleo, A., Inal, S., Rivnay, J. 2019; 29 (5)

  View details for DOI 10.1002/adfm.201807034

  View details for Web of Science ID 000457453300010

• Double doping of conjugated polymers with monomer molecular dopants NATURE MATERIALS Kiefer, D., Kroon, R., Hofmann, A. I., Sun, H., Liu, X., Giovannitti, A., Stegerer, D., Cano, A., Hynynen, J., Yu, L., Zhang, Y., Nai, D., Harrelson, T. F., Sommer, M., Moule, A. J., Kemerink, M., Marder, S. R., McCulloch, I., Fahlman, M., Fabiano, S., Mueller, C. 2019; 18 (2): 149-+

  Abstract

  Molecular doping is a crucial tool for controlling the charge-carrier concentration in organic semiconductors. Each dopant molecule is commonly thought to give rise to only one polaron, leading to a maximum of one donor:acceptor charge-transfer complex and hence an ionization efficiency of 100%. However, this theoretical limit is rarely achieved because of incomplete charge transfer and the presence of unreacted dopant. Here, we establish that common p-dopants can in fact accept two electrons per molecule from conjugated polymers with a low ionization energy. Each dopant molecule participates in two charge-transfer events, leading to the formation of dopant dianions and an ionization efficiency of up to 200%. Furthermore, we show that the resulting integer charge-transfer complex can dissociate with an efficiency of up to 170%. The concept of double doping introduced here may allow the dopant fraction required to optimize charge conduction to be halved.

  View details for DOI 10.1038/s41563-018-0263-6

  View details for Web of Science ID 000456325600016

  View details for PubMedID 30643236

• Subthreshold Operation of Organic Electrochemical Transistors for Biosignal Amplification ADVANCED SCIENCE Venkatraman, V., Friedlein, J. T., Giovannitti, A., Maria, I. P., McCulloch, I., McLeod, R. R., Rivnay, J. 2018; 5 (8): 1800453

  Abstract

  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 (gm), 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.

  View details for DOI 10.1002/advs.201800453

  View details for Web of Science ID 000441869400040

  View details for PubMedID 30128254

  View details for PubMedCentralID PMC6097142

• Direct metabolite detection with an n-type accumulation mode organic electrochemical transistor SCIENCE ADVANCES Pappa, A., Ohayon, D., Giovannitti, A., Maria, L., Savva, A., Uguz, I., Rivnay, J., McCulloch, L., Owens, R. M., Inal, S. 2018; 4 (6): eaat0911

  Abstract

  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.

  View details for DOI 10.1126/sciadv.aat0911

  View details for Web of Science ID 000443175500063

  View details for PubMedID 29942860

  View details for PubMedCentralID PMC6014717

• Lipid bilayer formation on organic electronic materials JOURNAL OF MATERIALS CHEMISTRY C Zhang, Y., Wustoni, S., Savva, A., Giovannitti, A., McCulloch, I., Inal, S. 2018; 6 (19): 5218–27

  View details for DOI 10.1039/c8tc00370j

  View details for Web of Science ID 000432599600016

• Enhanced n-Doping Efficiency of a Naphthalenediimide-Based Copolymer through Polar Side Chains for Organic Thermoelectrics ACS ENERGY LETTERS Kiefer, D., Giovannitti, A., Sun, H., Biskup, T., Hofmann, A., Koopmans, M., Cendra, C., Weber, S., Koster, L., Olsson, E., Rivnay, J., Fabiano, S., McCulloch, I., Muller, C. 2018; 3 (2): 278–85

  Abstract

  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.

  View details for PubMedID 29457139

• Liquid-Solid Dual-Gate Organic Transistors with Tunable Threshold Voltage for Cell Sensing ACS APPLIED MATERIALS & INTERFACES Zhang, Y., Li, J., Li, R., Sbircea, D., Giovannitti, A., Xu, J., Xu, H., Zhou, G., Bian, L., McCulloch, I., Zhao, N. 2017; 9 (44): 38687–94

  Abstract

  Liquid electrolyte-gated organic field effect transistors and organic electrochemical transistors have recently emerged as powerful technology platforms for sensing and simulation of living cells and organisms. For such applications, the transistors are operated at a gate voltage around or below 0.3 V because prolonged application of a higher voltage bias can lead to membrane rupturing and cell death. This constraint often prevents the operation of the transistors at their maximum transconductance or most sensitive regime. Here, we exploit a solid-liquid dual-gate organic transistor structure, where the threshold voltage of the liquid-gated conduction channel is controlled by an additional gate that is separated from the channel by a metal-oxide gate dielectric. With this design, the threshold voltage of the "sensing channel" can be linearly tuned in a voltage window exceeding 0.4 V. We have demonstrated that the dual-gate structure enables a much better sensor response to the detachment of human mesenchymal stem cells. In general, the capability of tuning the optimal sensing bias will not only improve the device performance but also broaden the material selection for cell-based organic bioelectronics.

  View details for DOI 10.1021/acsami.7b09384

  View details for Web of Science ID 000415140800057

  View details for PubMedID 29039186

• Sodium and Potassium Ion Selective Conjugated Polymers for Optical Ion Detection in Solution and Solid State ADVANCED FUNCTIONAL MATERIALS Giovannitti, A., Nielsen, C. B., Rivnay, J., Kirkus, M., Harkin, D. J., White, A. P., Sirringhaus, H., Malliaras, G. G., McCulloch, I. 2016; 26 (4): 514–23

  View details for DOI 10.1002/adfm.201503791

  View details for Web of Science ID 000368886000005

• Single and Multiple Additions of Dibenzoylmethane onto Buckminsterfullerene EUROPEAN JOURNAL OF ORGANIC CHEMISTRY Giovannitti, A., Seifermann, S. M., Bihlmeier, A., Muller, T., Topic, F., Rissanen, K., Nieger, M., Klopper, W., Braese, S. 2013; 2013 (35): 7907–13

  View details for DOI 10.1002/ejoc.201301146

  View details for Web of Science ID 000327775800010