9 research outputs found
Ferroelectric Polarization Induces Electric Double Layer Bistability in Electrolyte-Gated Field-Effect Transistors
The dense surface charges expressed
by a ferroelectric polymeric thin film induce ion displacement within
a polyelectrolyte layer and vice versa. This is because the density
of dipoles along the surface of the ferroelectric thin film and its
polarization switching time matches that of the (Helmholtz) electric
double layers formed at the ferroelectric/polyelectrolyte and polyelectrolyte/semiconductor
interfaces. This combination of materials allows for introducing hysteresis
effects in the capacitance of an electric double layer capacitor.
The latter is advantageously used to control the charge accumulation
in the semiconductor channel of an organic field-effect transistor.
The resulting memory transistors can be written at a gate voltage
of around 7 V and read out at a drain voltage as low as 50 mV. The
technological implication of this large difference between write and
read-out voltages lies in the non-destructive reading of this ferroelectric
memory
Double-Gate Light-Emitting Electrochemical Transistor: Confining the Organic pân Junction
In
conventional light-emitting electrochemical cells (LECs), an
off-centered pân junction is one of the major drawbacks, as
it leads to exciton quenching at one of the charge-injecting electrodes
and results in performance instability. To combat this problem, we
have developed a new device configuration, the double-gate light-emitting
electrochemical transistor (DG-LECT), in which the location of the
light-emitting pân junction can be precisely defined via the
position of the two gate terminals. Based on a planar LEC structure,
two gate electrodes made from an electrochemically active conducting
polymer are employed to predefine the p- and n-doped area of the light-emitting
polymer. Thus, a pân junction is formed in between the p-doped
and n-doped regions. We demonstrate a homogeneous and centered pân
junction as well as other predefined junction patterns in these DG-LECT
devices. Additionally, we report an electrical model that explains
the operation of the DG-LECTs. The DG-LECT device provides a new tool
to study the fundamental physics of LECs, as it dissects the key working
process of LEC into decoupled p-doping, n-doping, and electroluminescence
Organic Reprogrammable Circuits Based on Electrochemically Formed Diodes
We report a method to construct reprogrammable
circuits based on organic electrochemical (EC) pân junction
diodes. The diodes are built up from the combination of the organic
conjugated polymer polyÂ[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]
and a polymer electrolyte. The pân diodes are defined by EC
doping performed at 70 °C, and then stabilized at â30
°C. The reversible EC reaction allows for in situ reprogramming
of the polarity of the organic pân junction, thus enabling
us to reconfigure diode circuits. By combining diodes of specific
polarities dedicated circuits have been created, such as various logic
gates, a voltage limiter and an AC/DC converter. Reversing the EC
reaction allows in situ reprogramming of the pân junction polarity,
thus enabling reconfiguration of diode circuits, for example, from
an AND gate to an OR gate. The reprogrammable circuits are based on
pân diodes defined from only two layers, the electrodes and
then the active semiconductor:electrolyte composite material. Such
simple device structures are promising for large-area and fully printed
reconfigurable circuits manufactured using common printing tools.
The structure of the reported pân diodes mimics the architecture
of and is based on identical materials used to construct light-emitting
electrochemical cells (LEC). Our findings thus provide a robust signal
routing technology that is easily integrated with traditional LECs
Tuning the Thermoelectric Properties of Conducting Polymers in an Electrochemical Transistor
While organic field-effect transistors allow the investigation
of interfacial charge transport at the semiconductorâdielectric
interface, an electrochemical transistor truly modifies the oxidation
level and conductivity throughout the bulk of an organic semiconductor.
In this work, the thermoelectric properties of the bulk of the conducting
polymer polyÂ(3,4-ethylenedioxythiophene)âpolyÂ(styrene sulfonate)
were controlled electrically by varying the gate voltage. In light
of the growing interest in conducting polymers as thermoelectric generators,
this method provides an easy tool to study the physics behind the
thermoelectric properties and to optimize polymer thermoelectrics
Cross-Linked Nanocellulose Membranes for Nanofluidic Osmotic Energy Harvesting
Osmotic energy generated from the salinity gradient is
a kind of
clean and renewable energy source, where the ion-exchange membranes
play a critical role in its operation. The nanofluidic technique is
emerging to overcome the limitations of high resistance and low mass
transport of traditional ion-exchange membranes and thus improve osmotic
power conversion. However, the currently reported nanofluidic materials
suffer from high cost and complicated fabrication processes, which
limits their practical application. Here, we report low-cost nanocellulose
membranes that can be facilely prepared by a chemical cross-linking
approach. The obtained membranes exhibit excellent ion transport characteristics
as high-performance nanofluidic osmotic power generators. The control
of cross-linker dosage enables the simultaneous tunability of the
surface charge density and size of nanofluidic channels created between
the interwoven cellulose nanofibrils. The maximum osmotic power generated
by the membrane is reached when the cross-linker weight content is
20 wt %. Furthermore, the cross-linked nanocellulose membranes exhibit
long-term working stability in osmotic energy harvesting under a wide
range of pH values (3.2â9.7). This nanocellulose membrane derived
from green and sustainable natural materials demonstrates a promising
potential for renewable osmotic energy harvesting
Spatial Control of pân Junction in an Organic Light-Emitting Electrochemical Transistor
Low-voltage-operating organic electrochemical light-emitting
cells
(LECs) and transistors (OECTs) can be realized in robust device architectures,
thus enabling easy manufacturing of light sources using printing tools.
In an LEC, the pân junction, located within the organic semiconductor
channel, constitutes the active light-emitting element. It is established
and fixated through electrochemical p- and n-doping, which are governed
by charge injection from the anode and cathode, respectively. In an
OECT, the electrochemical doping level along the organic semiconducting
channel is controlled via the gate electrode. Here we report the merger
of these two devices: the light-emitting electrochemical transistor,
in which the location of the emitting pân junction and the
current level between the anode and cathode are modulated via a gate
electrode. Light emission occurs at 4 V, and the emission zone can
be repeatedly moved back and forth within an interelectrode gap of
500 ÎŒm by application of a 4 V gate bias. In transistor operation,
the estimated on/off ratio ranges from 10 to 100 with a gate threshold
voltage of â2.3 V and transconductance value between 1.4 and
3 ÎŒS. This device structure opens for new experiments tunable
light sources and LECs with added electronic functionality
Electronic Control over Detachment of a Self-Doped Water-Soluble Conjugated Polyelectrolyte
Water-soluble
conducting polymers are of interest to enable more
versatile processing in aqueous media as well as to facilitate interactions
with biomolecules. Here, we report a substituted polyÂ(3,4-ethylenedioxythiophene)
derivative (PEDOT-S:H) that is fully water-soluble and self-doped.
When electrochemically oxidizing a PEDOT-S:H thin film, the film detaches
from the underlying electrode. The oxidation of PEDOT-S:H starts with
an initial phase of swelling followed by cracking before it finally
disrupts into small flakes and detaches from the electrode. We investigated
the detachment mechanism and found that parameters such as the size,
charge, and concentration of ions in the electrolyte, the temperature,
and also the pH influence the characteristics of detachment. When
oxidizing PEDOT-S:H, the positively charged polymer backbone is balanced
by anions from the electrolyte solution and also by the sulfonate
groups on the side chains (more self-doping). From our experiments,
we conclude that detachment of the PEDOT-S:H film upon oxidation occurs
in part due to swelling caused by an inflow of solvated anions and
associated water and in part due to chain rearrangements within the
film, caused by more self-doping. We believe that PEDOT-S:H detachment
can be of interest in a number of different applications, including
addressed and active control of the release of materials such as biomolecules
and cell cultures
pH Dependence of ÎłâAminobutyric Acid Iontronic Transport
The organic electronic
ion pump (OEIP) has been developed as an
âiontronicâ tool for delivery of biological signaling
compounds. OEIPs rely on electrophoretically âpumpingâ
charged compounds, either at neutral or shifted pH, through an ion-selective
channel. Significant shifts in pH lead to an abundance of H<sup>+</sup> or OH<sup>â</sup>, which are delivered along with the intended
substance. While this method has been used to transport various neurotransmitters,
the role of pH has not been explored. Here we present an investigation
of the role of pH on OEIP transport efficiency using the neurotransmitter
Îł-aminobutyric acid (GABA) as the model cationic delivery substance.
GABA transport is evaluated at various pHs using electrical and chemical
characterization and compared to molecular dynamics simulations, all
of which agree that pH 3 is ideal for GABA transport. These results
demonstrate a useful method for optimizing transport of other substances
and thus broadening OEIP applications
Amphiphilic Poly(3-hexylthiophene)-Based Semiconducting Copolymers for Printing of Polyelectrolyte-Gated Organic Field-Effect Transistors
Polyelectrolytes are promising electronically
insulating layers for low-voltage organic field effect transistors.
However, the polyelectrolyteâsemiconductor interface is difficult
to manufacture due to challenges in wettability. We introduce an amphiphilic
semiconducting copolymer which, when spread as a thin film, can change
its surface from hydrophobic to hydrophilic upon exposure to water.
This peculiar wettability is exploited in the fabrication of polyelectrolyte-gated
field-effect transistors operating below 0.5 V. The prepared amphiphilic
semiconducting copolymer is based on a hydrophobic regioregular polyÂ(3-hexylthiophene)
(P3HT) covalently linked to a hydrophilic polyÂ(sulfonated)-based random
block. Such a copolymer is obtained in a three-step strategy combining
Grignard metathesis (GRIM), atom transfer radical polymerization (ATRP)
processes, and a postmodification method. The structure of the diblock
copolymer was characterized using FT-IR, <sup>1</sup>H NMR spectroscopy,
and gel permeation chromatography (GPC)