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

Solvent-Mediated Crystallization of CH₃NH₃SnI₃ Films for Heterojunction Depleted Perovskite Solar Cells

Organo-lead halide perovskite solar cells have gained enormous significance and have now achieved power conversion efficiencies of ∼20%. However, the potential toxicity of lead in these systems raises environmental concerns for widespread deployment. Here we investigate solvent effects on the crystallization of the lead-free methylammonium tin triiodide (CH₃NH₃SnI₃) perovskite films in a solution growth process. Highly uniform, pinhole-free perovskite films are obtained from a dimethyl sulfoxide (DMSO) solution via a transitional SnI₂·3DMSO intermediate phase. This high-quality perovskite film enables the realization of heterojunction depleted solar cells based on mesoporous TiO₂ layer but in the absence of any hole-transporting material with an unprecedented photocurrent up to 21 mA cm^–2. Charge extraction and transient photovoltage decay measurements reveal high carrier densities in the CH₃NH₃SnI₃ perovskite device which are one order of magnitude larger than CH₃NH₃PbI₃-based devices but with comparable recombination lifetimes in both devices. The relatively high background dark carrier density of the Sn-based perovskite is responsible for the lower photovoltaic efficiency in comparison to the Pb-based analogues. These results provide important progress toward achieving improved perovskite morphology control in realizing solution-processed highly efficient lead-free perovskite solar cells

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

Air-Stable Molecular Semiconducting Iodosalts for Solar Cell Applications: Cs₂SnI₆ as a Hole Conductor

We introduce a new class of molecular iodosalt compounds for application in next-generation solar cells. Unlike tin-based perovskite compounds CsSnI₃ and CH₃NH₃SnI₃, which have Sn in the 2+ oxidation state and must be handled in an inert atmosphere when fabricating solar cells, the Sn in the molecular iodosalt compounds is in the 4+ oxidation state, making them stable in air and moisture. As an example, we demonstrate that, using Cs₂SnI₆ as a hole transporter, we can successfully fabricate in air a solid-state dye-sensitized solar cell (DSSC) with a mesoporous TiO₂ film. Doping Cs₂SnI₆ with additives helps to reduce the internal device resistance, improving cell efficiency. In this way, a Z907 DSSC delivers 4.7% of energy conversion efficiency. By using a more efficient mixture of porphyrin dyes, an efficiency near 8% with photon confinement has been achieved. This represents a significant step toward the realization of low-cost, stable, lead-free, and environmentally benign next-generation solid-state solar cells

Buta-1,3-diyne-Based π‑Conjugated Polymers for Organic Transistors and Solar Cells

We report the synthesis and characterization of new alkyl-substituted 1,4-di­(thiophen-2-yl)­buta-1,3-diyne (R-DTB) donor building blocks, based on the −CC–CC– conjugative pathway, and their incorporation with thienyl-diketopyrrolo­pyrrole (R′-TDPP) acceptor units into π-conjugated PTDPP-DTB polymers (<b>P1</b>–<b>P4</b>). The solubility of the new polymers strongly depends on the DTB and DPP solubilizing (R and R′, respectively) substituents. Thus, solution processable and high molecular weight PDPP-DTB polymers are achieved for <b>P3</b> (R = <i>n</i>-C₁₂H₂₅, R′ = 2-butyloctyl) and <b>P4</b> (R = 2-ethylhexyl, R′ = 2-butyloctyl). Systematic studies of <b>P3</b> and <b>P4</b> physicochemical properties are carried using optical spectroscopy, cyclic voltammetry, and thermal analysis, revealing characteristic features of the dialkynyl motif. For the first time, optoelectronic devices (OFETs, OPVs) are fabricated with 1,3-butadiyne containing organic semiconductors. OFET hole mobilities and record OPV power conversion efficiencies for acetylenic organic materials approach 0.1 cm²/(V s) and 4%, respectively, which can be understood from detailed thin-film morphology and microstructural characterization using AFM, TEM, XRD, and GIWAXS methodologies. Importantly, DTB-based polymers (<b>P3</b> and <b>P4</b>) exhibit, in addition to stabilization of frontier molecular orbitals and to −CC–CC– relief of steric torsions, discrete morphological pliability through thermal annealing and processing additives. The advantageous materials properties and preliminary device performance reported here demonstrate the promise of 1,3-butadiyne-based semiconducting polymers

Slip-Stacked Perylenediimides as an Alternative Strategy for High Efficiency Nonfullerene Acceptors in Organic Photovoltaics

Perylenediimide (PDI)-based acceptors offer a potential replacement for fullerenes in bulk-heterojunction (BHJ) organic photovoltaic cells (OPVs). The most promising efforts have focused on creating twisted PDI dimers to disrupt aggregation and thereby suppress excimer formation. Here, we present an alternative strategy for developing high-performance OPVs based on PDI acceptors that promote slip-stacking in the solid state, thus preventing the coupling necessary for rapid excimer formation. This packing structure is accomplished by substitution at the PDI 2,5,8,11-positions (“headland positions”). Using this design principle, three PDI acceptors, <i>N</i>,<i>N</i>-bis­(n-octyl)-2,5,8,11-tetra­(<i>n</i>-hexyl)-PDI (<b>Hexyl-PDI</b>), <i>N</i>,<i>N</i>-bis­(n-octyl)-2,5,8,11-tetraphenethyl-PDI (<b>Phenethyl-PDI</b>), and <i>N</i>,<i>N</i>-bis­(n-octyl)-2,5,8,11-tetraphenyl-PDI (<b>Phenyl-PDI</b>), were synthesized, and their molecular and electronic structures were characterized. They were then blended with the donor polymer <b>PBTI3T</b>, and inverted OPVs of the structure ITO/ZnO/Active Layer/MoO₃/Ag were fabricated and characterized. Of these, 1:1 <b>PBTI3T</b>:<b>Phenyl-PDI</b> proved to have the best performance with <i>J</i>_sc = 6.56 mA/cm², <i>V</i>_oc = 1.024 V, FF = 54.59%, and power conversion efficiency (PCE) = 3.67%. Devices fabricated with <b>Phenethyl-PDI</b> and <b>Hexyl-PDI</b> have significantly lower performance. The thin film morphology and the electronic and photophysical properties of the three materials are examined, and although all three materials undergo efficient charge separation, <b>PBTI3T</b>:<b>Phenyl-PDI</b> is found to have the deepest LUMO, intermediate crystallinity, and the most well-mixed domains. This minimizes geminate recombination in <b>Phenyl-PDI</b> OPVs and affords the highest PCE. Thus, slip-stacked PDI strategies represent a promising approach to fullerene replacements in BHJ OPVs