4 research outputs found
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
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
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
Synthesis of PCDTBT-Based Fluorinated Polymers for High Open-Circuit Voltage in Organic Photovoltaics: Towards an Understanding of Relationships between Polymer Energy Levels Engineering and Ideal Morphology Control
The
introduction of fluorine (F) atoms onto conjugated polymer backbone
has verified to be an effective way to enhance the overall performance
of polymer-based bulk-heterojunction (BHJ) solar cells, but the underlying
working principles are not yet fully uncovered. As our attempt to
further understand the impact of F, herein we have reported two novel
fluorinated analogues of PCDTBT, namely, <b>PCDTFBT</b> (1F)
and <b>PCDT2FBT</b> (2F), through inclusion of either one or
two F atoms into the benzothiadiazole (BT) unit of the polymer backbone
and the characterization of their physical properties, especially
their performance in solar cells. Together with a profound effect
of fluorination on the optical property, nature of charge transport,
and molecular organization, F atoms are effective in lowering both
the HOMO and LUMO levels of the polymers without a large change in
the energy bandgaps. <b>PCDTFBT</b>-based BHJ solar cell shows
a power conversion efficiency (PCE) of 3.96 % with high open-circuit
voltage (<i>V</i><sub>OC</sub>) of 0.95 V, mainly due to
the deep HOMO level (−5.54 eV). To the best of our knowledge,
the resulting <i>V</i><sub>OC</sub> is comparable to the
record <i>V</i><sub>OC</sub> values in single junction devices.
Furthermore, to our delight, the best <b>PCDTFBT</b>-based device,
prepared using 2 % v/v diphenyl ether (DPE) additive, reaches the
PCE of 4.29 %. On the other hand, doubly-fluorinated polymer <b>PCDT2FBT</b> shows the only moderate PCE of 2.07 % with a decrease
in <i>V</i><sub>OC</sub> (0.88 V), in spite of the further
lowering of the HOMO level (−5.67 eV) with raising the number
of F atoms. Thus, our results highlight that an improvement in efficiency
by tuning the energy levels of the polymers by means of molecular
design can be expected only if their truly optimized morphologies
with fullerene in BHJ systems are materialized