Annulated Thienyl-Vinylene-Thienyl Building Blocks for π‑Conjugated Copolymers: Ring Dimensions and Isomeric Structure Effects on π‑Conjugation Length and Charge Transport

A series of annulated thienyl-vinylene-thienyl (<b>ATVT</b>) building blocks having varied ring sizes, isomeric structures, and substituents was synthesized and characterized by spectroscopic, electrochemical, quantum chemical, and crystallographic methods. It is found that <b>ATVT</b> ring size and isomeric structure critically affect the planarity, structural rigidity, optical absorption, and redox properties of these new π-units. Various solubilizing substituents can be introduced on the annulated hydrocarbon fragments, preserving the <b>ATVT</b> planarity and redox properties. The corresponding π-conjugated copolymers comprising <b>ATVT</b> units and electron-deficient units were also synthesized and characterized. The solubility, redox properties, and carrier transport behavior of these copolymers also depend remarkably on the annulated ring size and the <b>ATVT</b> unit isomeric structure. One of the copolymers composed of an <b>ATVT</b> with five-membered rings (<b>1</b>), (<i>E</i>)-4,4′,5,5′-tetrahydro-6,6′-bi­(cyclopenta­[<i>b</i>]­thiophenylidene), and a naphthalenediimide (<b>NDI</b>) unit exhibits a broad UV–vis–NIR absorption with an onset beyond 1100 nm both in solution and in the film state, and thin films exhibit n-type semiconducting properties in field-effect transistors. These results are ascribed to the extended main chain π-conjugation length and the low HOMO–LUMO bandgap. Other π-conjugated copolymers containing unit <b>1</b> also exhibit characteristic red-shifted UV–vis–NIR absorption. A diketopyrrolopyrrole-based copolymer with unit <b>1</b> serves as an electron donor material in organic photovoltaic devices, exhibiting broad-range external quantum efficiencies from the UV to beyond 1000 nm

Annulated Thienyl-Vinylene-Thienyl Building Blocks for π‑Conjugated Copolymers: Ring Dimensions and Isomeric Structure Effects on π‑Conjugation Length and Charge Transport

A series of annulated thienyl-vinylene-thienyl (<b>ATVT</b>) building blocks having varied ring sizes, isomeric structures, and substituents was synthesized and characterized by spectroscopic, electrochemical, quantum chemical, and crystallographic methods. It is found that <b>ATVT</b> ring size and isomeric structure critically affect the planarity, structural rigidity, optical absorption, and redox properties of these new π-units. Various solubilizing substituents can be introduced on the annulated hydrocarbon fragments, preserving the <b>ATVT</b> planarity and redox properties. The corresponding π-conjugated copolymers comprising <b>ATVT</b> units and electron-deficient units were also synthesized and characterized. The solubility, redox properties, and carrier transport behavior of these copolymers also depend remarkably on the annulated ring size and the <b>ATVT</b> unit isomeric structure. One of the copolymers composed of an <b>ATVT</b> with five-membered rings (<b>1</b>), (<i>E</i>)-4,4′,5,5′-tetrahydro-6,6′-bi­(cyclopenta­[<i>b</i>]­thiophenylidene), and a naphthalenediimide (<b>NDI</b>) unit exhibits a broad UV–vis–NIR absorption with an onset beyond 1100 nm both in solution and in the film state, and thin films exhibit n-type semiconducting properties in field-effect transistors. These results are ascribed to the extended main chain π-conjugation length and the low HOMO–LUMO bandgap. Other π-conjugated copolymers containing unit <b>1</b> also exhibit characteristic red-shifted UV–vis–NIR absorption. A diketopyrrolopyrrole-based copolymer with unit <b>1</b> serves as an electron donor material in organic photovoltaic devices, exhibiting broad-range external quantum efficiencies from the UV to beyond 1000 nm

Annulated Thienyl-Vinylene-Thienyl Building Blocks for π‑Conjugated Copolymers: Ring Dimensions and Isomeric Structure Effects on π‑Conjugation Length and Charge Transport

A series of annulated thienyl-vinylene-thienyl (<b>ATVT</b>) building blocks having varied ring sizes, isomeric structures, and substituents was synthesized and characterized by spectroscopic, electrochemical, quantum chemical, and crystallographic methods. It is found that <b>ATVT</b> ring size and isomeric structure critically affect the planarity, structural rigidity, optical absorption, and redox properties of these new π-units. Various solubilizing substituents can be introduced on the annulated hydrocarbon fragments, preserving the <b>ATVT</b> planarity and redox properties. The corresponding π-conjugated copolymers comprising <b>ATVT</b> units and electron-deficient units were also synthesized and characterized. The solubility, redox properties, and carrier transport behavior of these copolymers also depend remarkably on the annulated ring size and the <b>ATVT</b> unit isomeric structure. One of the copolymers composed of an <b>ATVT</b> with five-membered rings (<b>1</b>), (<i>E</i>)-4,4′,5,5′-tetrahydro-6,6′-bi­(cyclopenta­[<i>b</i>]­thiophenylidene), and a naphthalenediimide (<b>NDI</b>) unit exhibits a broad UV–vis–NIR absorption with an onset beyond 1100 nm both in solution and in the film state, and thin films exhibit n-type semiconducting properties in field-effect transistors. These results are ascribed to the extended main chain π-conjugation length and the low HOMO–LUMO bandgap. Other π-conjugated copolymers containing unit <b>1</b> also exhibit characteristic red-shifted UV–vis–NIR absorption. A diketopyrrolopyrrole-based copolymer with unit <b>1</b> serves as an electron donor material in organic photovoltaic devices, exhibiting broad-range external quantum efficiencies from the UV to beyond 1000 nm

Synergistic Approach to High-Performance Oxide Thin Film Transistors Using a Bilayer Channel Architecture

We report here a bilayer metal oxide thin film transistor concept (bMO TFT) where the channel has the structure: dielectric/semiconducting indium oxide (In₂O₃) layer/semiconducting indium gallium oxide (IGO) layer. Both semiconducting layers are grown from solution via a low-temperature combustion process. The TFT mobilities of bottom-gate/top-contact bMO TFTs processed at <i>T</i> = 250 °C are ∼5tmex larger (∼2.6 cm²/(V s)) than those of single-layer IGO TFTs (∼0.5 cm²/(V s)), reaching values comparable to single-layer combustion-processed In₂O₃ TFTs (∼3.2 cm²/(V s)). More importantly, and unlike single-layer In₂O₃ TFTs, the threshold voltage of the bMO TFTs is ∼0.0 V, and the current on/off ratio is significantly enhanced to ∼1 × 10⁸ (vs ∼1 × 10⁴ for In₂O₃). The microstructure and morphology of the In₂O₃/IGO bilayers are analyzed by X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, revealing the polycrystalline nature of the In₂O₃ layer and the amorphous nature of the IGO layer. This work demonstrates that solution-processed metal oxides can be implemented in bilayer TFT architectures with significantly enhanced performance

Synergistic Approach to High-Performance Oxide Thin Film Transistors Using a Bilayer Channel Architecture

We report here a bilayer metal oxide thin film transistor concept (bMO TFT) where the channel has the structure: dielectric/semiconducting indium oxide (In₂O₃) layer/semiconducting indium gallium oxide (IGO) layer. Both semiconducting layers are grown from solution via a low-temperature combustion process. The TFT mobilities of bottom-gate/top-contact bMO TFTs processed at <i>T</i> = 250 °C are ∼5tmex larger (∼2.6 cm²/(V s)) than those of single-layer IGO TFTs (∼0.5 cm²/(V s)), reaching values comparable to single-layer combustion-processed In₂O₃ TFTs (∼3.2 cm²/(V s)). More importantly, and unlike single-layer In₂O₃ TFTs, the threshold voltage of the bMO TFTs is ∼0.0 V, and the current on/off ratio is significantly enhanced to ∼1 × 10⁸ (vs ∼1 × 10⁴ for In₂O₃). The microstructure and morphology of the In₂O₃/IGO bilayers are analyzed by X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, revealing the polycrystalline nature of the In₂O₃ layer and the amorphous nature of the IGO layer. This work demonstrates that solution-processed metal oxides can be implemented in bilayer TFT architectures with significantly enhanced performance

Cross-Linkable Molecular Hole-Transporting Semiconductor for Solid-State Dye-Sensitized Solar Cells

In this study, we investigate the use of a cross-linkable organosilane semiconductor, 4,4′-bis­[(<i>p</i>-trichlorosilylpropylphenyl)­phenylamino]­biphenyl (TPDSi₂), as a hole-transporting material (HTM) for solid-state dye-sensitized solar cells (ssDSSCs) using the standard amphiphilic Z907 dye which is compatible with organic HTM deposition. The properties and performance of the resulting cells are then compared and contrasted with the ones based on poly­(3-hexylthiophene) (P3HT), a conventional polymeric HTM, but with rather limited pore-filling capacity. When processed under N₂, TPDSi₂ exhibits excellent infiltration into the mesoporous TiO₂ layer and thus enables the fabrication of relatively thick devices (∼5 μm) for efficient photon harvesting. When exposed to ambient atmosphere (RH_amb ∼ 20%), TPDSi₂ readily undergoes cross-linking to afford a rigid, thermally stable hole-transporting layer. In addition, the effect of <i>tert</i>-butylpyridine (TBP) and lithium bis­(trifluoromethylsulfonyl)­imide salt (Li-TFSI) additives on the electrochemical properties of these HTMs is studied via a combination of cyclic voltammetry (CV) and ultraviolet photoemission spectroscopy (UPS) measurements. The results demonstrate that the additives significantly enhance the space charge limited current (SCLC) mobilities for both the P3HT and TPDSi₂ HTMs and induce a shift in the TPDSi₂ Fermi level, likely a p-doping effect. These combined effects of improved charge transport characteristics for the TPDSi₂ devices enhance the power conversion efficiency (PCE) by more than 2-fold for ssDSSCs

Perfluoroalkyl-Functionalized Thiazole–Thiophene Oligomers as N‑Channel Semiconductors in Organic Field-Effect and Light-Emitting Transistors

Despite their favorable electronic and structural properties, the synthetic development and incorporation of thiazole-based building blocks into <i>n</i>-type semiconductors has lagged behind that of other π-deficient building blocks. Since thiazole insertion into π-conjugated systems is synthetically more demanding, continuous research efforts are essential to underscore their properties in electron-transporting devices. Here, we report the design, synthesis, and characterization of a new series of thiazole–thiophene tetra- (<b>1</b> and <b>2</b>) and hexa-heteroaryl (<b>3</b> and <b>4</b>) co-oligomers, varied by core extension and regiochemistry, which are end-functionalized with electron-withdrawing perfluorohexyl substituents. These new semiconductors are found to exhibit excellent <i>n</i>-channel OFET transport with electron mobilities (μ_<i>e</i>) as high as 1.30 cm²/(V·s) (<i>I</i>_on/<i>I</i>_off > 10⁶) for films of <b>2</b> deposited at room temperature. In contrary to previous studies, we show here that 2,2′-bithiazole can be a very practical building block for high-performance <i>n</i>-channel semiconductors. Additionally, upon 2,2′- and 5,5′-bithiazole insertion into a sexithiophene backbone of well-known <b>DFH-6T</b>, significant charge transport improvements (from 0.001–0.021 cm²/(V·s) to 0.20–0.70 cm²/(V·s)) were observed for <b>3</b> and <b>4</b>. Analysis of the thin-film morphological and microstructural characteristics, in combination with the physicochemical properties, explains the observed high mobilities for the present semiconductors. Finally, we demonstrate for the first time implementation of a thiazole semiconductor (<b>2</b>) into a trilayer light-emitting transistor (OLET) enabling green light emission. Our results show that thiazole is a promising building block for efficient electron transport in π-conjugated semiconductor thin-films, and it should be studied more in future optoelectronic applications

Bithiophenesulfonamide Building Block for π‑Conjugated Donor–Acceptor Semiconductors

We report here π-conjugated small molecules and polymers based on the new π-acceptor building block, bithiophenesulfonamide (BTSA). Molecular orbital computations and optical, electrochemical, and crystal structure analyses illuminate the architecture and electronic structure of the BTSA unit versus other acceptor building blocks. Field-effect transistors and photovoltaic cells demonstrate that BTSA is a promising unit for the construction of π-conjugated semiconducting materials

Marked Consequences of Systematic Oligothiophene Catenation in Thieno[3,4‑<i>c</i>]pyrrole-4,6-dione and Bithiopheneimide Photovoltaic Copolymers

As effective building blocks for high-mobility transistor polymers, oligothiophenes are receiving attention for polymer solar cells (PSCs) because the resulting polymers can effectively suppress charge recombination. Here we investigate two series of in-chain donor–acceptor copolymers, <b>PTPDnT</b> and <b>PBTInT</b>, based on thieno­[3,4-<i>c</i>]­pyrrole-4,6-dione (<b>TPD</b>) or bithiopheneimide (<b>BTI</b>) as electron acceptor units, respectively, and oligothiophenes (<b>nT</b>s) as donor counits, for high-performance PSCs. Intramolecular S···O interaction leads to more planar <b>TPD</b> polymer backbones, however backbone torsion yields greater open-circuit voltages for <b>BTI</b> polymers. Thiophene addition progressively raises polymer HOMOs but marginally affects their band gaps. FT-Raman spectra indicate that <b>PTPDnT</b> and <b>PBTInT</b> conjugation lengths scale with <b>nT</b> catenation up to <i>n</i> = 3 and then saturate for longer oligomer. Furthermore, the effects of oligothiophene alkylation position are explored, revealing that the alkylation pattern greatly affects film morphology and PSC performance. The <b>3T</b> with “outward” alkylation in <b>PTPD3T</b> and <b>PBTI3T</b> affords optimal π-conjugation, close stacking, long-range order, and high hole mobilities (0.1 cm²/(V s)). These characteristics contribute to the exceptional ∼80% fill factors for <b>PTPD3T</b>-based PSCs with PCE = 7.7%. The results demonstrate that <b>3T</b> is the optimal donor unit among <b>nT</b>s (<i>n</i> = 1–4) for photovoltaic polymers. Grazing incidence wide-angle X-ray scattering, transmission electron microscopy, and time-resolved microwave conductivity measurements reveal that the terthiophene-based <b>PTPD3T</b> blend maintains high crystallinity with appreciable local mobility and long charge carrier lifetime. These results provide fundamental materials structure-device performance correlations and suggest guidelines for designing oligothiophene-based polymers with optimal thiophene catenation and appropriate alkylation pattern to maximize PSC performance