This review summarises high performing n-type polymers for use in organic thin film transistors, organic electrochemical transistors and organic thermoelectric devices with a focus on stability issues arising in these electron transporting materials.
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.
Recent research demonstrates the viability of organic electrochemical transistors (OECTs) as an emergent technology for biosensor applications. Herein, a comprehensive summary is provided, highlighting the significant progress and most notable advances within the field of OECT‐based biosensors. The working principles of an OECT are detailed, with specific attention given to the current library of organic mixed ionic‐electronic conductor (OMIEC) channel materials utilized in OECT biosensors. The application of OECTs for metabolite, ion, neuromorphic, electrophysiological, and virus sensing as well as immunosensing is reported, detailing the breadth and scope of OECT‐based biosensors. Furthermore, an outlook and perspective on synthetic molecular design of future channel materials, specifically designed for OECT biosensors, is provided. The development of optimized channel materials, creative device architectures, and operational nuances will set the stage for OECT‐based biosensors to thrive and accelerate their clinical prevalence in the near future.
A series
of fully fused n-type mixed conduction lactam polymers
p(g
7
NC
n
N)
, systematically increasing
the alkyl side chain content, are synthesized via an inexpensive,
nontoxic, precious-metal-free aldol polycondensation. Employing these
polymers as channel materials in organic electrochemical transistors
(OECTs) affords state-of-the-art n-type performance with
p(g
7
NC
10
N)
recording an OECT electron mobility of 1.20 ×
10
–2
cm
2
V
–1
s
–1
and a μ
C
* figure of merit
of 1.83 F cm
–1
V
–1
s
–1
. In parallel to high OECT performance, upon solution doping with
(4-(1,3-dimethyl-2,3-dihydro-1
H
-benzoimidazol-2-yl)phenyl)dimethylamine
(N-DMBI), the highest thermoelectric performance is observed for
p(g
7
NC
4
N)
, with a maximum electrical conductivity of
7.67 S cm
–1
and a power factor of 10.4 μW
m
–1
K
–2
. These results are among
the highest reported for n-type polymers. Importantly, while this
series of fused polylactam organic mixed ionic–electronic conductors
(OMIECs) highlights that synthetic molecular design strategies to
bolster OECT performance can be translated to also achieve high organic
thermoelectric (OTE) performance, a nuanced synthetic approach must
be used to optimize performance. Herein, we outline the performance
metrics and provide new insights into the molecular design guidelines
for the next generation of high-performance n-type materials for mixed
conduction applications, presenting for the first time the results
of a single polymer series within both OECT and OTE applications.
On-site signal amplification for bioelectronic sensing is a desirable approach to improving recorded signal quality and to reducing the burden on signal transmission and back-end electronics. While organic electrochemical transistors (OECTs) have been used as local transducers of bioelectronic signals, their current output presents challenges for implementation. OECT-based circuits offer new opportunities for high-performance signal processing. In this work, we introduce an active sensing node based on cofacial vertical OECTs forming an ambipolar complementary inverter. The inverter, which shows a voltage gain of 28, is composed of two OECTs on opposite side walls of a single active area, resulting in a footprint identical to a planar OECT. The inverter is used as an analog voltage preamplifier for recording electrocardiogram signals when biased at the input voltage corresponding to peak gain. We further demonstrate compatibility with nontraditional fabrication methods with potential benefits for rapid prototyping and large-area printed electronics.
A nonfullerene acceptor, isoIDITC, capable of exhibiting fibril-like morphology, is utilized as a third component in organic photovoltaics (OPVs). A power conversion efficiency (PCE) of 19% is achieved in ternary...
Propylene and butylene glycol oligoether chains have been employed as alternatives to ethylene glycol in thiophene based semiconductors for OECTs. Their impact on electrochemical, microstructure, and swelling properties are discussed.
Electrochemical transistors (ECTs) have shown broad applications in bioelectronics and neuromorphic devices due to their high transconductance, low working voltage, and versatile device design. To further improve the device performance, semiconductor materials with both high carrier mobilities and large capacitances in electrolytes are needed. Here, we demonstrate ECTs based on highly oriented two-dimensional conjugated metal-organic frameworks (2D c-MOFs). The ion-conductive vertical nanopores formed within the 2D c-MOFs films lead to the most convenient ion transfer in the bulk and high volumetric capacitance, endowing the devices with fast speeds and ultrahigh transconductance. Ultraflexible device arrays are successfully used for wearable on-skin recording of electrocardiogram (ECG) signals along different directions, which can provide various waveforms comparable with those of multilead ECG measurement systems for monitoring heart conditions. These results indicate that 2D c-MOFs are excellent semiconductor materials for high-performance ECTs with promising applications in flexible and wearable electronics.
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