Until now, only limited DPP oligomers delivered ambipolar semiconductor characteristics. To develop a facile strategy of preparing ambipolar mono-DPP oligomers, two dithienyl diketopyrrolopyrrole ...(DPPT) based-conjugated molecules, DPPT-RD and DPPT-DCV, which contain 3-ethylrhodanine (RD) and dicyano-2-vinyl (DCV) end substituents were synthesized. The influences of the -RD end substituents on the molecular properties, solid-state morphology, and OFET performances of the DPPT oligomer were investigated. The UV–vis absorption and CV results showed that the RD end substituents provide the DPPT oligomer suitable E HOMO and E LUMO for hole and electron injection from the Au source-drain electrodes. Moreover, the RD end substituents also improve the crystalline nature of the DPPT oligomer. That is, DPPT-RD can form crystal arrays with good lattice orientation, larger crystalline size, and without polymorphism. With those properties, DPPT-RD thus display ambipolar characteristic with μh and μe reaching 2.16 × 10–2 and 7.27 × 10–2 cm2 V–1 s–1, respectively.
D–A conjugated molecules are complicated in both their molecular and their packing structures. In this perspective, we summarize more than 40 crystal lattices of conjugated oligomers to identify the ...morphological influence of each building block on the D–A molecules. These lattice structures reveal not only the packing preferences of the conjugated oligomers but also the conformational disorder in the lattices. The presence of this disorder in slowly grown crystals implies that attaining total long-range conformational order is challenging for D–A oligomers, which are structurally complicated and readily distorted and which have building blocks of incommensurate packing dimensions. In optoelectronic applications, a decreased duration of processing can prevent ordering and trap the thin films of D–A oligomers from becoming crystalline phases. Although D–A oligomers conform to packing principles in the formation of a single crystal, their phase behaviors in the formation of active thin films are much more difficult to comprehend. Continuous advances in methods of characterization are still strongly required for the steps of attaining a true structure–property relation of D–A oligomers in active films for optoelectronic applications.
The physical properties, packing, morphology, and semiconducting performance of a planar π-conjugated system can be effectively modified by introducing side chains and substituent groups, both of ...which can be complementary to the π framework in changing the intermolecular association, frontier molecular orbital energy, optical band gap, and others. We herein show that installation of end-capped electron-withdrawing groups (EWGs), such as dicyanovinyl (−DCV), 3-ethylrhodanine (−RD), and 2-(3-oxo-indan-1-ylidene)-malononitrile (−INCN), together with siloxane side chains to the backbones of dithienyldiketopyrrolopyrrole (DPPT), such as DPPT-Si-DCV, DPPT-Si-RD, and DPPT-Si-INCN, can greatly improve its solubility, air stability, and film morphology to serve as an n-channel in thin-film transistor fabrication. The EWGs attached to the DPPT core narrowed the optical band gap (E g opt) and changed the highest occupied molecular orbital and the lowest unoccupied molecular orbital energies (E HOMO and E LUMO), making them suitable for n-channel field-effect transistor (FET) applications. The benefits of introducing siloxane side chains to the DPPT core include enhanced solubility, low crystallization barrier, enantiotropic phase behavior, and much improved FET performance. The DPPT-Si-INCN film displayed low-lying HOMO (−5.82 eV) and LUMO (−4.60 eV) energy levels and an optical band gap as low as 1.22 eV, all of which suggest that this derivative can be quite resistant toward aerial oxidation. Thin films of these derivatives were prepared by the solution-shear method. A comparison of the solution-sheared films indicated that the molecular packing motif of DPPT-Si-INCN film was somehow different from that of DPPT-Si-DCV and DPPT-Si-RD, in which the π–π stacking tended to align orthogonally to the shearing direction. This specific π–π stacking alignment could have an impact on the electron mobility (μe) values in transistors based on the solution-sheared films.
Here, two diketopyrrolopyrrole (DPP)-based oligomers, DPP-4T and DPP-6T, are studied to reveal the influences of conjugation length on thin-film morphology and organic field-effect transistor (OFET) ...performances. PDMS-assisted crystallization in a solvent-annealing chamber is applied to prepare crystal arrays of DPP-4T and DPP-6T to optimize the quality of charge channels for OFET characterizations. To deliver insights into microstructure and morphology of thin films, a characterization procedure for determining molecular packing in thin film and crystallinity of the crystal arrays is presented via grazing incidence wide-angle X-ray scattering, electron diffraction, and lattice simulation software package (Cerius2). With the lattice parameters derived from analyses of grazing incidence wide-angle X-ray scattering (GIWAXS) and electron diffraction (ED), the lattice modeling results indicate that the inferior organic field-effect transistor (OFET) performances of DPP-6T are attributed to longer π-stacking distance. Also, less-ordered molecular arrangement and lower continuity of crystalline domains, both of which are revealed from crystallinity results, lead to lower mobility of DPP-6T. In this case, longer conjugated backbones with more conformational degrees of freedom thus cause inherent crystal defects during the crystal growth process, despite the potential to enhance intermolecular π-orbital overlap. Therefore, to achieve better OFET performance, suitable backbone length makes conjugated oligomers give high intermolecular π-orbital overlap and low density of structural disorder, which are the priorities for constructing good charge channel.
An A–D–A oligomer, DTS(F2BT)2, was synthesized; its structural evolution was studied with DSC, POM, 2D-WAXD, and in-situ GI-XRD. The structural evolution of DTS(F2BT)2 is stepwise and kinetically ...slow. Both rapid drying and the presence of PC71BM trapped DTS(F2BT)2 in a less ordered nematic (N) phase. PDMS-assisted crystallization enabled a pristine DTS(F2BT)2 thin film to attain a more ordered equilibrium phase, and enhanced the OFET mobility of DTS(F2BT)2. In OPV devices, DIO additive drove the DTS(F2BT)2 domains in the DTS(F2BT)2:PC71BM blended film from the N phase toward the equilibrium phase, and resulted in enhanced OPV performances. These results reveal the slow ordering process of the A–D–A oligomer, and the importance of monitoring the degree of structural evolution of the active thin films in organic optoelectronics.
The authors report the growth of TiO 2 nanowires by heating the Ti/glass template and the fabrication of a TiO 2 nanowire metal-insulator-semiconductor (MIS) photodetector (PD). Compared with a TiO 2 ...nanowire metal-semiconductor- metal PD, it was found that we could achieve a photocurrent 29 times larger. It was also found that the dynamic response of the TiO 2 nanowire MIS PD was stable and reproducible with an on/off current contrast ratio of around 180. With an incident light wavelength of 390 nm and an applied bias of 5 V, it was found that the measured responsivity of the PD was 2.46 × 10 -3 A/W. Furthermore, the noise equivalent power and the detectivity of the fabricated TiO 2 nanowire MIS PD were 7.49 × 10 -12 W and 8.86 × 10 11 cm · Hz 0.5 · W -1 , respectively.
A giant amphiphile, which is constructed with an amorphous nano-pyramid (triphenylamine, TPA) and a crystalline nano-sphere (C
), was synthesized. Structural characterization indicates that this ...pyramid-sphere-shaped amphiphile (
) forms a solvent-induced ordered phase, in which the two constituent units self-assemble into alternating stacks of two-dimensional (2D) TPA and C
nano-sheets. Due to the complexity of the molecular structure and the amorphous nature of the nano-pyramid, phase formation was driven by intermolecular C
-C
interactions and the ordered phase could not be reformed from the
melt. Oriented crystal arrays of
, which contain flat-on TPA/C
nano-stacks, can be obtained
a PDMS-assisted crystallization (PAC) technique. The flat-on dual-channel supramolecular structure of
delivered ambipolar and balanced charge-transport characteristics with an average
of 2.11 × 10
cm
V
s
and
of 3.37 × 10
cm
V
s
. The anisotropic charge-transport ability of the pyramid-sphere-shaped amphiphile was further understood based on the lattice structure and the lattice orientation of
revealed from electron diffraction analyses.
A giant amphiphile, which is constructed with an amorphous nano-pyramid (triphenylamine, TPA) and a crystalline nano-sphere (C
60
), was synthesized. Structural characterization indicates that this ...pyramid-sphere-shaped amphiphile (
TPA-C
60
) forms a solvent-induced ordered phase, in which the two constituent units self-assemble into alternating stacks of two-dimensional (2D) TPA and C
60
nano-sheets. Due to the complexity of the molecular structure and the amorphous nature of the nano-pyramid, phase formation was driven by intermolecular C
60
-C
60
interactions and the ordered phase could not be reformed from the
TPA-C
60
melt. Oriented crystal arrays of
TPA-C
60
, which contain flat-on TPA/C
60
nano-stacks, can be obtained
via
a PDMS-assisted crystallization (PAC) technique. The flat-on dual-channel supramolecular structure of
TPA-C
60
delivered ambipolar and balanced charge-transport characteristics with an average
μ
e
of 2.11 × 10
−4
cm
2
V
−1
s
−1
and
μ
h
of 3.37 × 10
−4
cm
2
V
−1
s
−1
. The anisotropic charge-transport ability of the pyramid-sphere-shaped amphiphile was further understood based on the lattice structure and the lattice orientation of
TPA-C
60
revealed from electron diffraction analyses.
The study identified the flat-on dual-channel nano-structure and the ambipolar characteristics of a novel giant pyramid-sphere shape amphiphile.
A giant amphiphile, which is constructed with an amorphous nano-pyramid (triphenylamine, TPA) and a crystalline nano-sphere (C sub(60)), was synthesized. Structural characterization indicates that ...this pyramid-sphere-shaped amphiphile (TPA-C sub(60)) forms a solvent-induced ordered phase, in which the two constituent units self-assemble into alternating stacks of two-dimensional (2D) TPA and C sub(60) nano-sheets. Due to the complexity of the molecular structure and the amorphous nature of the nano-pyramid, phase formation was driven by intermolecular C sub(60)-C sub(60) interactions and the ordered phase could not be reformed from the TPA-C sub(60) melt. Oriented crystal arrays of TPA-C sub(60), which contain flat-on TPA/C sub(60) nano-stacks, can be obtained viaa PDMS-assisted crystallization (PAC) technique. The flat-on dual-channel supramolecular structure of TPA-C sub(60) delivered ambipolar and balanced charge-transport characteristics with an average mu sub(e) of 2.11 10 super(-4) cm super(2) V super(-1) s super(-1) and mu sub(h) of 3.37 10 super(-4) cm super(2) V super(-1) s super(-1). The anisotropic charge-transport ability of the pyramid-sphere-shaped amphiphile was further understood based on the lattice structure and the lattice orientation of TPA-C sub(60) revealed from electron diffraction analyses.
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