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Papers by Jonathan Javier Sayago Hoyos
The n-type organic semiconductor phenyl-C 61-butyric acid methyl ester (PCBM), a soluble fulleren... more The n-type organic semiconductor phenyl-C 61-butyric acid methyl ester (PCBM), a soluble fullerene derivative well investigated for organic solar cells and transistors, can undergo several successive reversible, diffusion-controlled, one-electron reduction processes. We exploited such processes to shed light on the correlation between electron transfer properties, ionic and electronic transport as well as device performance in ionic liquid (IL)-gated transistors. Two ILs were considered, based on bis(trifluoromethylsulfonyl)imide [TFSI] as the anion and 1-ethyl-3-methylimidazolium [EMIM] or 1-butyl-1-methylpyrrolidinium [PYR 14 ] as the cation. The aromatic structure of [EMIM] and its lower steric hindrance with respect to [PYR 14 ] favor a 3D (bulk) electrochemical doping. As opposed to this, for [PYR 14 ] the doping seems to be 2D (surface-confined). If the n-doping of the PCBM is pursued beyond the first electrochemical process, the transistor current vs. gate-source voltage plots in [PYR 14 ][TFSI] feature a maximum that points to the presence of finite windows of high conductivity in IL-gated PCBM transistors.
In electrolyte-gated transistors, the exceptionally high capacitance of the electrical double lay... more In electrolyte-gated transistors, the exceptionally high capacitance of the electrical double layer forming at the electrolyte/transistor channel interface permits current modulations of several orders of magnitude, at relatively low gate voltages. The effect of the nature of the gate electrode on the performance of electrolyte-gated transistors is still largely unclear, despite recent intensive efforts. Here we demonstrate that the use of high surface area, low cost, activated carbon gate electrode enables low voltage (sub-1 V) operation in ionic liquid-gated organic transistors and renders unnecessary the presence of an external reference electrode to monitor the channel potential, thus dramatically simplifying the device structure. We used the organic electronic polymer MEH-PPV (poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene), as the channel material, and the high ionic conductivity, low viscosity ionic liquid [EMIM] [TFSI] (1-ethyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide), as the electrolyte gating material. We believe that this will prove to be the first of a new generation of low voltage electrolyte-gated transistors for applications in organic printable electronics.
The electrical properties of eumelanin, a ubiquitous natural pigment, have fascinated scientists ... more The electrical properties of eumelanin, a ubiquitous natural pigment, have fascinated scientists since the late 1960s. For several decades, the hydration-dependent electrical properties of eumelanin have mainly been interpreted within the amorphous semiconductor model. Recent works undermined this paradigm. Here we study protonic and electronic charge carrier transport in hydrated eumelanin in thin film form. Thin films are ideal candidates for these studies since they are readily accessible to chemical and morphological characterization and potentially amenable to device applications. Current−voltage (I-V) measurements, transient current measurements with proton-transparent electrodes, and electrochemical impedance spectros-copy (EIS) measurements are reported and correlated with the results of the chemical characterization of the films, performed by X-ray photoelectron spectroscopy. We show that the electrical response of hydrated eumelanin films is dominated by ionic conduction (10 −4 −10 −3 S cm −1), largely attributable to protons, and electrochemical processes. To propose an explanation for the electrical response of hydrated eumelanin films as observed by EIS and I-V, we considered the interplay of proton migration, redox processes, and electronic transport. These new insights improve the current understanding of the charge carrier transport properties of eumelanin opening the possibility to assess the potential of eumelanin for organic bioelectronic applications, e.g. protonic devices and implantable electrodes, and to advance the knowledge on the functions of eumelanin in biological systems.
We report the proof-of-concept of the TransCap, a monolithically integrated device that exhibits ... more We report the proof-of-concept of the TransCap, a monolithically integrated device that exhibits the storage properties of a supercapacitor and the low-voltage operation of an electrolyte-gated transistor. The proof-of-concept is based on coupling a polymer channel with a high surface area carbon gate, employing an ionic liquid as the electrolyte. The possibility to recover the stored energy from the TransCap permits us to use it to power different microelectronic components. † Electronic supplementary information (ESI) available: Fig. S1: transistor transfer characteristics of the [N 1113 ][TFSI]-gated MEH-PPV TransCap in saturation. Experimental details on: polymer thin lm deposition; ionic liquid purication; device fabrication; TransCap electrochemical and electrical characterization. See
The impressive improvement in biomolecular detection has gone from simple chemical methods to sop... more The impressive improvement in biomolecular detection has gone from simple chemical methods to sophisticated high throughput laboratory machines capable of accurately measuring the complex biological components and interactions. In the following chap‐ ter, we focus our attention on transistor‐based devices as an emerging platform for easy‐to‐use, portable amplified biodetection for preventive personalized medical appli‐ cations and point‐of‐care testing. Electronic sensing devices comprise biosensors based on field‐effect transistors (bio‐FETs) and organic electrochemical transistors (OECTs). Transistor sensing devices can transduce electronic and ionic signals thereby creat‐ ing an effective human‐machine communication channel. In this chapter, we survey the progress done on the development of transistor innovative concepts to examine biological processes, i.e., biosensors integrated with textiles, flexible substrates, and biocompatible materials. Electrochemical and field‐effect transistors can operate at low voltages possibly serving for highly sensitive, selective, and real‐time sensing devices. The exploration of biosensors integrates different disciplines such as organic electronics, biology, electrochemistry, and materials science.
The n-type organic semiconductor phenyl-C 61-butyric acid methyl ester (PCBM), a soluble fulleren... more The n-type organic semiconductor phenyl-C 61-butyric acid methyl ester (PCBM), a soluble fullerene derivative well investigated for organic solar cells and transistors, can undergo several successive reversible, diffusion-controlled, one-electron reduction processes. We exploited such processes to shed light on the correlation between electron transfer properties, ionic and electronic transport as well as device performance in ionic liquid (IL)-gated transistors. Two ILs were considered, based on bis(trifluoromethylsulfonyl)imide [TFSI] as the anion and 1-ethyl-3-methylimidazolium [EMIM] or 1-butyl-1-methylpyrrolidinium [PYR 14 ] as the cation. The aromatic structure of [EMIM] and its lower steric hindrance with respect to [PYR 14 ] favor a 3D (bulk) electrochemical doping. As opposed to this, for [PYR 14 ] the doping seems to be 2D (surface-confined). If the n-doping of the PCBM is pursued beyond the first electrochemical process, the transistor current vs. gate-source voltage plots in [PYR 14 ][TFSI] feature a maximum that points to the presence of finite windows of high conductivity in IL-gated PCBM transistors.
In electrolyte-gated transistors, the exceptionally high capacitance of the electrical double lay... more In electrolyte-gated transistors, the exceptionally high capacitance of the electrical double layer forming at the electrolyte/transistor channel interface permits current modulations of several orders of magnitude, at relatively low gate voltages. The effect of the nature of the gate electrode on the performance of electrolyte-gated transistors is still largely unclear, despite recent intensive efforts. Here we demonstrate that the use of high surface area, low cost, activated carbon gate electrode enables low voltage (sub-1 V) operation in ionic liquid-gated organic transistors and renders unnecessary the presence of an external reference electrode to monitor the channel potential, thus dramatically simplifying the device structure. We used the organic electronic polymer MEH-PPV (poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene), as the channel material, and the high ionic conductivity, low viscosity ionic liquid [EMIM] [TFSI] (1-ethyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide), as the electrolyte gating material. We believe that this will prove to be the first of a new generation of low voltage electrolyte-gated transistors for applications in organic printable electronics.
The electrical properties of eumelanin, a ubiquitous natural pigment, have fascinated scientists ... more The electrical properties of eumelanin, a ubiquitous natural pigment, have fascinated scientists since the late 1960s. For several decades, the hydration-dependent electrical properties of eumelanin have mainly been interpreted within the amorphous semiconductor model. Recent works undermined this paradigm. Here we study protonic and electronic charge carrier transport in hydrated eumelanin in thin film form. Thin films are ideal candidates for these studies since they are readily accessible to chemical and morphological characterization and potentially amenable to device applications. Current−voltage (I-V) measurements, transient current measurements with proton-transparent electrodes, and electrochemical impedance spectros-copy (EIS) measurements are reported and correlated with the results of the chemical characterization of the films, performed by X-ray photoelectron spectroscopy. We show that the electrical response of hydrated eumelanin films is dominated by ionic conduction (10 −4 −10 −3 S cm −1), largely attributable to protons, and electrochemical processes. To propose an explanation for the electrical response of hydrated eumelanin films as observed by EIS and I-V, we considered the interplay of proton migration, redox processes, and electronic transport. These new insights improve the current understanding of the charge carrier transport properties of eumelanin opening the possibility to assess the potential of eumelanin for organic bioelectronic applications, e.g. protonic devices and implantable electrodes, and to advance the knowledge on the functions of eumelanin in biological systems.
We report the proof-of-concept of the TransCap, a monolithically integrated device that exhibits ... more We report the proof-of-concept of the TransCap, a monolithically integrated device that exhibits the storage properties of a supercapacitor and the low-voltage operation of an electrolyte-gated transistor. The proof-of-concept is based on coupling a polymer channel with a high surface area carbon gate, employing an ionic liquid as the electrolyte. The possibility to recover the stored energy from the TransCap permits us to use it to power different microelectronic components. † Electronic supplementary information (ESI) available: Fig. S1: transistor transfer characteristics of the [N 1113 ][TFSI]-gated MEH-PPV TransCap in saturation. Experimental details on: polymer thin lm deposition; ionic liquid purication; device fabrication; TransCap electrochemical and electrical characterization. See
The impressive improvement in biomolecular detection has gone from simple chemical methods to sop... more The impressive improvement in biomolecular detection has gone from simple chemical methods to sophisticated high throughput laboratory machines capable of accurately measuring the complex biological components and interactions. In the following chap‐ ter, we focus our attention on transistor‐based devices as an emerging platform for easy‐to‐use, portable amplified biodetection for preventive personalized medical appli‐ cations and point‐of‐care testing. Electronic sensing devices comprise biosensors based on field‐effect transistors (bio‐FETs) and organic electrochemical transistors (OECTs). Transistor sensing devices can transduce electronic and ionic signals thereby creat‐ ing an effective human‐machine communication channel. In this chapter, we survey the progress done on the development of transistor innovative concepts to examine biological processes, i.e., biosensors integrated with textiles, flexible substrates, and biocompatible materials. Electrochemical and field‐effect transistors can operate at low voltages possibly serving for highly sensitive, selective, and real‐time sensing devices. The exploration of biosensors integrates different disciplines such as organic electronics, biology, electrochemistry, and materials science.