16 research outputs found
Nature-Inspired Semiconducting Polymers with Peptide Conjugation Breakers for Intrinsically Stretchable and Self-Healable Transistors
Intrinsically stretchable and self-healable polymer semiconductors
have recently been extensively studied for flexible and wearable electronics.
However, challenges lie in the scarcity of molecular designs, laborious
synthesis, and an incomplete understanding of energy dissipation mechanisms.
Nature-inspired peptide conjugation breakers (PCBs) can provide a
robust system for expanding the molecular scope systematically due
to the structural diversity of peptides concerning steric bulkiness
and polarity. In this study, novel intrinsically stretchable and self-healable
semiconducting polymers are developed by integrating PCBs into a diketopyrrolopyrrole
moiety, and the distinct roles of intermolecular and intramolecular
hydrogen bonds in stretchability are investigated. The former mainly
disrupts chain packing and results in reduced crystallinity, while
the latter restricts the conformational flexibility of the chain.
Remarkably, the polymer containing a glycine-based PCB demonstrates
a high mobility of 0.12 cm2 V–1 s–1 with good cyclic durability and a crack-onset strain
exceeding 100%. Mobility remains stable even at 100% strain in both
rigid and fully stretchable transistors with self-healing characteristics.
These results, for the first time, underscore the usefulness of nature-inspired
moieties in stretchable and self-healable electronics and provide
a molecular design strategy that balances intermolecular and intramolecular
hydrogen bonds, thereby yielding desirable electrical and mechanical
properties
Naphthalene Diimide Incorporated Thiophene-Free Copolymers with Acene and Heteroacene Units: Comparison of Geometric Features and Electron-Donating Strength of Co-units
A family of naphthalene diimide (NDI)-based
donor (D)-acceptor
(A) copolymers with various acene- (benzene (Bz), naphthalene (Np),
and pyrene (Py)) and heteroacene-type (selenophene (Se) and thiophene
(Th)) donor rings has been designed and synthesized as a means to
systematically understand structure–property relationships
on the subject of the structural factor and electron-donating capability
of the donor portions for applications in organic field-effect transistors
(OFETs) based on NDIs. Alongside of two categories dealing with the
lack or existence of the heteroatoms in the donor framework, the resulting
copolymers can also be classified into ‘thiophene-free’
D–A copolymers (<b>PNDI-Bz</b>, <b>PNDI-Np</b>, <b>PNDI-Py</b>, and <b>PNDI-Se</b>) and thiophene-containing
copolymer (<b>PNDI-Th</b>). The results from optical and electronic
properties lead to the determination that the empirical electron-donating
strength of donor co-units is in the order of Bz < Np < Py <
Th < Se. In contrast with the similarity of the LUMO levels (−3.73∼−3.82
eV) due to the dominant NDI contribution to the polymer backbone,
the HOMO levels are sensitive to the relative electron-donating ability
and shown to primarily influence whether unipolar <i>n</i>-channel (<b>PNDI-Bz</b> and <b>PNDI-Np</b>) or ambipolar
charge transport (<b>PNDI-Py</b>, <b>PNDI-Se</b>, and <b>PNDI-Th</b>) is observed in OFETs of the NDI-based copolymers.
Intriguingly, regardless of the strong electron donors toward efficient
intramolecular charge transfer (ICT), the best OFET performance is
observed in the acene-based centrosymmetric copolymer <b>PNDI-Np</b> (5.63 × 10<sup>–2</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>) when compared to those of the other copolymers
with axisymmetric units. Thus, the present work highlights that the
geometric features of the donors in NDI D–A copolymers strongly
reflect the carrier mobility dynamics rather than inserting electron-rich
donor moieties into the backbone to lower the band gap and further
strengthen ICT
β‑Alkyl substituted Dithieno[2,3‑<i>d</i>;2′,3′<i>-d</i>′]benzo[1,2‑<i>b</i>;4,5‑<i>b</i>′]dithiophene Semiconducting Materials and Their Application to Solution-Processed Organic Transistors
A novel highly π-extended heteroacene with four
symmetrically
fused thiophene-ring units and solubilizing substituents at the terminal
β-positions on the central ring, dithienoÂ[2,3-<i>d</i>;2′,3′<i>-d</i>′]ÂbenzoÂ[1,2-<i>b</i>;4,5-<i>b</i>′]Âdithiophene (DTBDT) was
synthesized via intramolecular electrophilic coupling reaction. The
α-positions availability in the DTBDT motif enables the preparation
of solution-processable DTBDT-based polymers such as <b>PDTBDT</b>, <b>PDTBDT-BT</b>, <b>PDTBDT-DTBT</b>, and <b>PDTBDT-DTDPP</b>. Even with its highly extended acene-like π-framework, all
polymers show fairly good environmental stability of their highest
occupied molecular orbitals (HOMOs) from −5.21 to −5.59
eV. In the course of our study to assess a profile of semiconductor
properties, field-effect transistor performance of the four DTBDT-containing
copolymers via solution-process is characterized, and <b>PDTBDT-DTDPP</b> exhibits the best electrical performance with a hole mobility of
1.70 × 10<sup>–2</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. <b>PDTBDT-DTDPP</b> has a relatively
smaller charge injection barrier for a hole from the gold electrodes
and maintains good coplanarity of the polymer backbone, indicating
the enhanced π–π stacking characteristic and charge
carrier transport. The experimental results demonstrate that our molecular
design strategy for air-stable, high-performance organic semiconductors
is highly promising
Solution-Processable Ambipolar Diketopyrrolopyrrole–Selenophene Polymer with Unprecedentedly High Hole and Electron Mobilities
There is a fast-growing demand for polymer-based ambipolar
thin-film transistors (TFTs), in which both <i>n</i>-type
and <i>p</i>-type transistor operations are realized in
a single layer, while maintaining simplicity in processing. Research
progress toward this end is essentially fueled by molecular engineering
of the conjugated backbones of the polymers and the development of
process architectures for device fabrication, which has recently led
to hole and electron mobilities of more than 1.0 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. However, ambipolar polymers
with even higher performance are still required. By taking into account
both the conjugated backbone and side chains of the polymer component,
we have developed a dithienyl-diketopyrrolopyrrole (TDPP) and selenophene
containing polymer with hybrid siloxane-solubilizing groups (<b>PTDPPSe-Si</b>). A synergistic combination of rational polymer
backbone design, side-chain dynamics, and solution processing affords
an enormous boost in ambipolar TFT performance, resulting in unprecedentedly
high hole and electron mobilities of 3.97 and 2.20 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, respectively
Boosting the Ambipolar Performance of Solution-Processable Polymer Semiconductors via Hybrid Side-Chain Engineering
Ambipolar polymer semiconductors
are highly suited for use in flexible,
printable, and large-area electronics as they exhibit both <i>n</i>-type (electron-transporting) and <i>p</i>-type
(hole-transporting) operations within a single layer. This allows
for cost-effective fabrication of complementary circuits with high
noise immunity and operational stability. Currently, the performance
of ambipolar polymer semiconductors lags behind that of their unipolar
counterparts. Here, we report on the side-chain engineering of conjugated,
alternating electron donor–acceptor (D–A) polymers using
diketopyrrolopyrrole-selenophene copolymers with hybrid siloxane-solubilizing
groups (<b>PTDPPSe-Si</b>) to enhance ambipolar performance.
The alkyl spacer length of the hybrid side chains was systematically
tuned to boost ambipolar performance. The optimized three-dimensional
(3-D) charge transport of <b>PTDPPSe-Si</b> with pentyl spacers
yielded unprecedentedly high hole and electron mobilities of 8.84
and 4.34 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, respectively. These results provide guidelines for the molecular
design of semiconducting polymers with hybrid side chains
Requirements for Forming Efficient 3‑D Charge Transport Pathway in Diketopyrrolopyrrole-Based Copolymers: Film Morphology vs Molecular Packing
To
achieve extremely high planarity and processability simultaneously,
we have newly designed and synthesized copolymers composed of donor
units of 2,2′-(2,5-dialkoxy-1,4-phenylene)ÂdithienoÂ[3,2-<i>b</i>]Âthiophene (TT-P-TT) and acceptor units of diketopyrrolopyrrole
(DPP). These copolymers consist of a highly planar backbone due to
intramolecular interactions. We have systematically investigated the
effects of intermolecular interactions by controlling the side chain
bulkiness on the polymer thin-film morphologies, packing structures,
and charge transport. The thin-film microstructures of the copolymers
are found to be critically dependent upon subtle changes in the intermolecular
interactions, and charge transport dynamics of the copolymer based
field-effect transistors (FETs) has been investigated by in-depth
structure–property relationship study. Although the size of
the fibrillar structures increases as the bulkiness of the side chains
in the copolymer increases, the copolymer with the smallest side chain
shows remarkably high charge carrier mobility. Our findings reveal
the requirement for forming efficient 3-D charge transport pathway
and highlight the importance of the molecular packing and interdomain
connectivity, rather than the crystalline domain size. The results
obtained herein demonstrate the importance of tailoring the side chain
bulkiness and provide new insights into the molecular design for high-performance
polymer semiconductors
Fluorinated Benzothiadiazole (BT) Groups as a Powerful Unit for High-Performance Electron-Transporting Polymers
Over the past few years, one of the
most remarkable advances in the field of polymer solar cells (PSCs)
has been the development of fluorinated 2,1,3-benzothiadiazole (BT)-based
polymers that lack the solid working principles of previous designs,
but boost the power conversion efficiency. To assess a rich data set
for the influence of the fluorinated BT units on the charge-transport
characteristics in organic field-effect transistors (OFETs), we synthesized
two new polymers (<b>PDPP-FBT</b> and <b>PDPP-2FBT</b>) incorporating diketopyrrolopyrrole (DPP) and either single- or
double-fluorinated BT and thoroughly investigated them via a range
of techniques. Unlike the small differences in the absorption properties
of <b>PDPP-FBT</b> and its nonfluorinated analogue (<b>PDPP-BT</b>), the introduction of doubly fluorinated BT into the polymer backbone
induces a noticeable change in its optical profiles and energy levels,
which results in a slightly wider bandgap and deeper HOMO for <b>PDPP-2FBT</b>, relative to the others. Grazing incidence X-ray
diffraction (GIXD) analysis reveals that both fluorinated polymer
films have long-range orders along the out-of-plane direction, and
π–π stacking in the in-plane direction, implying
semicrystalline lamellar structures with edge-on orientations in the
solid state. Thanks to the strong intermolecular interactions and
highly electron-deficient π-systems driven by the inclusion
of F atoms, the polymers exhibit electron mobilities of up to 0.42
and 0.30 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> for <b>PDPP-FBT</b> and <b>PDPP-2FBT</b>, respectively,
while maintaining hole mobilities higher than 0.1 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. Our results highlight that
the use of fluorinated BT blocks in the polymers is a promising molecular
design strategy for improving electron transporting performance without
sacrificing their original hole mobility values
Determining Optimal Crystallinity of Diketopyrrolopyrrole-Based Terpolymers for Highly Efficient Polymer Solar Cells and Transistors
A new series of conjugated random
terpolymers (PDPP2T-Se-Th) was
synthesized from an electron-deficient diketopyrrolopyrrole (DPP)-based
unit in conjugation with two electron-rich selenophene (Se) and thiophene
(Th) species, with a view to inducing different crystalline behaviors
of the polymers. The crystallinity of the polymers can be systematically
controlled by tuning the ratio between Se and Th; an increase in Se
content induced a remarkable increase in the melting and crystallization
temperatures as well as the crystallinity of the PDPP2T-Se-Th terpolymers.
These changes in the crystalline properties of polymers had a dramatic
effect on the performances of organic field-effect transistors (OFETs)
and polymer solar cells (PSCs). However, their effect on each type
of devices was very different. The charge carrier mobilities of the
PDPP2T-Se-Th terpolymers in OFET devices increased remarkably as the
Se content increased in the polymers, showing that PDPP2T-Se100 with
Se/Th ratio = 100/0 had very high hole and electron mobilities (4.72
and 5.54 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, respectively) with well-balanced ambipolar property. In contrast,
the best power conversion efficiency (PCE) of 7.2% was observed for
the PDPP2T-Se10-Th90 polymers that had Se/Th ratio of 10/90 due to
the synergistic contributions from high charge mobility and optimized
bulk-heterojunction (BHJ) morphology with fullerene acceptors. To
understand the effects of the crystallinity of random terpolymers
on their performances in OTFTs and PSCs, we systematically investigated
the effects of the Se/Th compositions on their optical, electrical,
and structural properties
Polarity and Air-Stability Transitions in Field-Effect Transistors Based on Fullerenes with Different Solubilizing Groups
A series of <i>o</i>-xylene
and indene fullerene derivatives with varying frontier molecular orbital
energy levels were utilized for assessing the impact of the number
of solubilizing groups on the electrical performance of fullerene-based
organic-field-effect transistors (OFETs). The charge-carrier polarity
was found to be strongly dependent upon the energy levels of fullerene
derivatives. The <i>o</i>-xylene C<sub>60</sub> monoadduct
(OXCMA) and indene C<sub>60</sub> monoadduct (ICMA) exhibited unipolar <i>n</i>-channel behaviors with high electron mobilities, whereas
the bis- and trisadducts of indene and <i>o</i>-xylene C<sub>60</sub> derivatives showed ambipolar charge transport. The OXCMA
OFETs fabricated by solution shearing and molecular <i>n</i>-type doping showed an electron mobility of up to 2.28 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, which is one of the
highest electron mobilities obtained from solution-processed fullerene
thin-film devices. Our findings systematically demonstrate the relationship
between the energy level and charge-carrier polarity and provide insight
into molecular design and processing strategies toward high-performance
fullerene-based OFETs
Ambipolar Semiconducting Polymers with <i>Ï€-</i>Spacer Linked Bis-Benzothiadiazole Blocks as Strong Accepting Units
Recognizing the importance of molecular
coplanarity and with the
aim of developing new, ideal strong acceptor-building units in semiconducting
polymers for high-performance organic electronics, herein we present
a simplified single-step synthesis of novel vinylene- and acetylene-linked
bis-benzothiadiazole (<b>VBBT</b> and <b>ABBT</b>) monomers
with enlarged planarity relative to a conventionally used acceptor,
benzothiadiazole (BT). Along these lines, four polymers (<b>PDPP-VBBT</b>, <b>PDPP-ABBT</b>, <b>PIID-VBBT</b>, and <b>PIID-ABBT</b>) incorporating either <b>VBBT</b> or <b>ABBT</b> moieties
are synthesized by copolymerizing with centro-symmetric ketopyrrole
cores, such as diketopyrrolopyrrole (DPP) and isoindigo (IID), and
their electronic, physical, and transistor properties are studied.
These polymers show relatively balanced ambipolar transport, and <b>PDPP-VBBT</b> yields hole and electron mobilities as high as 0.32
and 0.13 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, respectively. Interestingly, the acetylenic linkages lead to enhanced
electron transportation in ketopyrrole-based polymers, showing a decreased
threshold voltage and inverting voltage in the transistor and inverter
devices, respectively. The IID-based BBT polymers exhibit the inversion
of the dominant polarity depending on the type of unsaturated carbon
bridge. Owing to their strong electron-accepting ability and their
highly π-extended and planar structures, <b>VBBT</b> and <b>ABBT</b> monomers should be extended to the rational design of
high-performance polymers in the field of organic electronics