Thieno[3,4-c]pyrrole-4,6-dione-Based Polymer Semiconductors: Toward High-Performance, Air-Stable Organic Thin-Film Transistors

Ambipolar Heterojunction Sensors: Another Way to Detect Polluting Gases

Gas sensors based on ambipolar materials offer significant advantages in reducing the size of the analytical system and enhancing its efficiency. Here, bilayer heterojunction devices are constructed using different octafluorinated phthalocyanine complexes, with Zn and Co as metal centers, combined with a lutetium bisphthalocyanine complex (LuPc2). Stable p-type behavior is observed for the ZnF8Pc/LuPc2 device under both electron-donating (NH3) and -oxidizing (NO2 and O3) gaseous species, while the CoF8Pc/LuPc2 device exhibits n-type behavior under reducing gases and p-type behavior under oxidizing gases. The nature of majority of the charge carriers of Co-based devices varies depending on the nature of target gases, displaying an ambipolar behavior. Both heterojunction devices demonstrate stable and observable response toward all three toxic gases in the sub-ppm range. Remarkably, the Co-based device is highly sensitive toward ammonia with a limit of detection (LOD) of 200 ppb, whereas the Zn-based device demonstrates exceptional sensitivity toward oxidizing gases, with excellent LOD values of 4.9 and 0.75 ppb toward NO2 and O3, respectively, which makes it one of the most effective organic heterojunction sensors reported so far for oxidizing gases.

Tuning Dipole Orientation of 2,6-Azulene Units in Conjugated Copolymers by C–H Activation Strategy toward High-Performance Organic Semiconductor

Azulene has aroused widespread interest for constructing optoelectronic materials. However, controlling the dipole orientation of 2,6-azulene units in the conjugated polymer backbone is a significant challenge so far. Herein, by C-H activation strategy, three 2,6-azulene-TPD-based conjugated copolymers with different dipole arrangements were synthesized, where TPD = thieno[3,4-c]pyrrole-4,6-dione. The dipole arrangements of 2,6-azulene units were random for P(AzTPD-1), head-to-head/tail-to-tail for P(AzTPD-2), and head-to-tail for P(AzTPD-3). These polymers exhibited unipolar n-type semiconductor characteristics in organic field effect transistors. Moreover, regioregular polymer P(AzTPD-3) displayed the best device performance with an electron mobility of up to 0.33 cm² V^-1 s^-1, which makes P(AzTPD-3) a high-performance n-type polymeric semiconductor. These results demonstrate that incorporation of 2,6-azulene units into the polymeric backbone together with the regulation of the dipole orientation of 2,6-azulene units is an effective strategy for obtaining high-performance organic optoelectronic materials.

A cyano-based electron-accepting building block to design n-type conjugated polymers with absorption wavelength of >1000 nm

There are much fewer n-type conjugated polymers than p-type counterparts because of the lack of strong electron-accepting building blocks. We report a novel strong electron-accepting unit based on a dicyanomethylene unit. The resulting polymers exhibit LUMO energy levels of as low as -4.04 eV and narrow optical gaps with an onset absorption wavelength of 1050 nm. Moreover, the polymers exhibit near-infrared light absorption with good photostability because of their low-lying LUMO/HOMO energy levels.

A Four-Component Reaction for the Synthesis of Thienopyrrolediones under Transition Metal Free Conditions

A three-starting-material four-component reaction strategy is described to construct thienopyrrolediones (TPDs) from the simplest raw materials, elemental sulfur, aldehydes, and β-ketoamides, under transition metal free conditions. Compared with traditional multistep reaction sequences, this process is simple, efficient, environmentally friendly, and atom-economic and has laid the foundation for further development of an easily synthesized TPD unit.

Acceptor Modulation Strategies for Improving the Electron Transport in High-Performance Organic Field-Effect Transistors

High-performance ambipolar and electronic type semiconducting polymers are essential for fabricating various organic optoelectronic devices and complementary circuits. This review summarizes the strategies of improving the electron transport of semiconducting polymers via acceptor modulation strategies, which include the use of single, dual, triple, multiple, and all acceptors as well as the fusion of multiple identical acceptors to obtain new heterocyclic acceptors. To further improve the electron transport of semiconducting polymers, the introduction of strong electron-withdrawing groups can enhance the electron-withdrawing ability of donors and acceptors, thereby facilitating electron injection and suppressing hole accumulation. In addition, the relationships between the molecular structure, frontier molecular orbital energy levels, thin film morphology, microstructure, processing conditions, and device performances are also comprehensively discussed. Finally, the challenges encountered in this research area are proposed and the future outlook is presented.

A Direct Writing Approach for Organic Semiconductor Single-Crystal Patterns with Unique Orientation

Organic semiconductor single-crystal (OSSC) patterns with precisely controlled orientation are of great significance to the integrated fabrication of devices with high and uniform performance. However, it is still challenging to achieve purely oriented OSSC patterns due to the complex nucleation and growth process of OSSCs. Here, a general direct writing approach is presented to readily obtain high-quality OSSC patterns with unique orientation. In specific, a direct writing method is demonstrated wherein the microscale meniscus is manipulated, which makes it possible to precisely control the nucleation and growth process of the OSSC because of its comparable size to the crystal nuclei. The resulting OSSC patterns are highly crystalline and purely oriented, in which each ribbon crystal shows a deviation angle of 33° to the printing direction. The mechanism of orientation purification is revealed experimentally and theoretically, and the results show that the TCL deformation caused by the difference in wettability and adhesive force, as well as the asymmetry of fluid concentration distribution, are the key factors leading to the selective deposition and unique orientation. Moreover, organic field-effect transistors (OFETs) and polarization-sensitive photodetectors are prepared based on the OSSC patterns with unique orientation, which exhibit higher device performance compared to the non-purely oriented crystal-based OFETs.

Donor–acceptor π-conjugated polymers based on terthiophene-3,4-dicarboxylate, dithienopyrrolobenzothiadiazole and thieno[3,4-c]pyrrole-4,6-dione units and their hole mobility

We have synthesized three different p-type donor–acceptor π-conjugated polymers based on diethyl [2,2′:5′,2′′-terthiophene]-3′,4′-dicarboxylate, dithienopyrrolobenzothiadiazole and thieno[3,4-c]pyrrole-4,6-dione units.

Thiophene-Based Trimers and Their Bioapplications: An Overview

Certainly, the success of polythiophenes is due in the first place to their outstanding electronic properties and superior processability. Nevertheless, there are additional reasons that contribute to arouse the scientific interest around these materials. Among these, the large variety of chemical modifications that is possible to perform on the thiophene ring is a precious aspect. In particular, a turning point was marked by the diffusion of synthetic strategies for the preparation of terthiophenes: the vast richness of approaches today available for the easy customization of these structures allows the finetuning of their chemical, physical, and optical properties. Therefore, terthiophene derivatives have become an extremely versatile class of compounds both for direct application or for the preparation of electronic functional polymers. Moreover, their biocompatibility and ease of functionalization make them appealing for biology and medical research, as it testifies to the blossoming of studies in these fields in which they are involved. It is thus with the willingness to guide the reader through all the possibilities offered by these structures that this review elucidates the synthetic methods and describes the full chemical variety of terthiophenes and their derivatives. In the final part, an in-depth presentation of their numerous bioapplications intends to provide a complete picture of the state of the art.

Multi-level aggregation of conjugated small molecules and polymers: from morphology control to physical insights

Aggregation of molecules is a multi-molecular phenomenon occurring when two or more molecules behave differently from discrete molecules due to their intermolecular interactions. Moving beyond single molecules, aggregation usually demonstrates evolutive or wholly emerging new functionalities relative to the molecular components. Conjugated small molecules and polymers interact with each other, resulting in complex solution-state aggregates and solid-state microstructures. Optoelectronic properties of conjugated small molecules and polymers are sensitively determined by their aggregation states across a broad range of spatial scales. This review focused on the aggregation ranging from molecular structure, intermolecular interactions, solution-state assemblies, and solid-state microstructures of conjugated small molecules and polymers. We addressed the importance of such aggregation in filling the gaps from the molecular level to device functions and highlighted the multi-scale structures and properties at different scales. From the view of multi-level aggregation behaviors, we divided the whole process from the molecule to devices into several parts: molecular design, solvation, solution-state aggregation, crystal engineering, and solid-state microstructures. We summarized the progress and challenges of relationships between optoelectronic properties and multi-level aggregation. We believe aggregation science will become an interdisciplinary research field and serves as a general platform to develop future materials with the desired functions.

Capturing Mobile Lithium Ions in a Molecular Hole Transporter Enhances the Thermal Stability of Perovskite Solar Cells

A thermally stable perovskite solar cell (PSC) based on a new molecular hole transporter (MHT) of 1,3-bis(5-(4-(bis(4-methoxyphenyl) amino)phenyl)thieno[3,2-b]thiophen-2-yl)-5-octyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (coded HL38) is reported. Hole mobility of 1.36 × 10^-3 cm² V^-1 s^-1 and glass transition temperature of 92.2 °C are determined for the HL38 doped with lithium bis(trifluoromethanesulfonyl)imide and 4-tert-butylpyridine as additives. Interface engineering with 2-(2-aminoethyl)thiophene hydroiodide (2-TEAI) between the perovskite and the HL38 improves the power conversion efficiency (PCE) from 19.60% (untreated) to 21.98%, and this champion PCE is even higher than that of the additive-containing 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeOTAD)-based device (21.15%). Thermal stability testing at 85 °C for over 1000 h shows that the HL38-based PSC retains 85.9% of the initial PCE, while the spiro-MeOTAD-based PSC degrades unrecoverably from 21.1% to 5.8%. Time-of-flight secondary-ion mass spectrometry studies combined with Fourier transform infrared spectroscopy reveal that HL38 shows lower lithium ion diffusivity than spiro-MeOTAD due to a strong complexation of the Li⁺ with HL38, which is responsible for the higher degree of thermal stability. This work delivers an important message that capturing mobile Li⁺ in a hole-transporting layer is critical in designing novel MHTs for improving the thermal stability of PSCs. In addition, it also highlights the impact of interface design on non-conventional MHTs.

Air-Stable and High-Performance Unipolar n-Type Conjugated Semiconducting Polymers Prepared by a "Strong Acceptor-Weak Donor" Strategy

Unipolar n-type conjugated polymer materials with long-term stable electron transport upon direct exposure to the air atmosphere are very challenging to prepare. In this study, three unipolar n-type donor-acceptor (D-A) conjugated polymer semiconductors (abbreviated as PNVB, PBABDFV, and PBAIDV) were successfully developed through a "strong acceptor-weak donor" strategy. The weak electron donation of the donor units in all three polymers successfully lowered the molecular energy levels by the acceptor units that strongly attracted electrons. Cyclic voltammetry demonstrated that all three polymers had low highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels near -6.0 and -4.0 eV, respectively. These results were consistent with the density functional theory calculations. The as-prepared polymers were then used to manufacture organic field-effect transistor (OFET) devices in bottom-gate/top-contact (BG/TC) configuration without any packaging protection. As expected, all devices exhibited unipolar electron transport properties. PBABDFV-based devices showed excellent field-effect performance and air stability, beneficial for straight-line molecular chain and closest π-π stacking distance to prevent water vapor and oxygen from diffusion into the active layer. This led to a maximum electron mobility (μ_e,max) of 0.79 cm² V^-1 s^-1 under air conditions. In addition, 0.50 cm² V^-1 s^-1 was still maintained after 27 days of storage in ambient environment. The near-ideal transfer curve of the PBABDFV-based OFET device in BG/TC configuration under vacuum was obtained with average mobility reliability factor (r_ave) reaching 88%.

A Solution-Processable meso-Phenyl-BODIPY-Based n-Channel Semiconductor with Enhanced Fluorescence Emission

The molecular design, synthesis, and characterization of an acceptor-donor-acceptor (A-D-A) semiconductor BDY-Ph-2T-Ph-BDY comprising a central phenyl-bithiophene-phenyl π-donor and BODIPY π-acceptor end-units is reported. The semiconductor shows an optical band gap of 2.32 eV with a highly stabilized HOMO/LUMO (-5.74 eV/-3.42 eV). Single-crystal X-ray diffraction (XRD) reveals D-A dihedral angle of ca. 66° and strong intermolecular "C-H ⋅⋅⋅ π (3.31 Å)" interactions. Reduced π-donor strength, increased D-A dihedral angle, and restricted intramolecular D-A rotations allows for both good fluorescence efficiency (Φ_F =0.30) and n-channel OFET transport (μ_e =0.005 cm² /V ⋅ s; I_on /I_off =10⁴ -10⁵ ). This indicates a much improved (6-fold) fluorescence quantum yield compared to the meso-thienyl BODIPY semiconductor BDY-4T-BDY. Photophysical studies reveal important transitions between locally excited (LE) and twisted intramolecular charge-transfer (TICT) states in solution and the solid state, which could be controlled by solvent polarity and nano-aggregation. This is the first report of such high emissive characteristics for a BODIPY-based n-channel semiconductor.

Solution-processable BODIPY decorated triazine photodiodes and their comprehensive photophysical evaluation

Solution-processed organic photodiodes can function as thin-film candidates for solid-state photosensors in various optoelectronic applications due to the physical and chemical tuneability.

Backbone Coplanarity Tuning of 1,4-Di(3-alkoxy-2-thienyl)-2,5-difluorophenylene-Based Wide Bandgap Polymers for Efficient Organic Solar Cells Processed from Nonhalogenated Solvent

Halogenated solvents are prevailingly used in the fabrication of nonfullerene organic solar cells (NF-OSCs) at the current stage, imposing significant restraints on their practical applications. By copolymerizing phthalimide or thieno[3,4-c]pyrrole-4,6-dione (TPD) with 1,4-di(3-alkoxy-2-thienyl)-2,5-difluorophenylene (DOTFP), which features intramolecular noncovalent interactions, the backbone planarity of the resulting DOTFP-based polymers can be effectively tuned, yielding distinct solubilities, aggregation characters, and chain packing properties. Polymer DOTFP-PhI with a more twisted backbone showed a lower degree of aggregation in solution but an increased film crystallinity than polymer DOTFP-TPD. An organic thin-film transistor and NF-OSC based on DOTFP-PhI, processed with a nonhalogenated solvent, exhibited a high hole mobility up to 1.20 cm² V^-1 s^-1 and a promising power conversion efficiency up to 10.65%, respectively. The results demonstrate that DOTFP is a promising building block for constructing wide bandgap polymers and backbone coplanarity tuning is an effective strategy to develop high-performance organic semiconductors processable with a nonhalogenated solvent.

Significant Difference in Semiconducting Properties of Isomeric All-Acceptor Polymers Synthesized via Direct Arylation Polycondensation

The direct arylation polycondensation (DArP) appeared as an efficient method for producing semiconducting polymers but often requires acceptor monomers with orienting or activating groups for the reactive carbon-hydrogen (C-H) bonds, which limits the choice of acceptor units. In this study, we describe a DArP for producing high-molecular-weight all-acceptor polymers composed of the acceptor monomers without any orienting or activating groups via a modified method using Pd/Cu co-catalysts. We thus obtained two isomeric all-acceptor polymers, P1 and P2, which have the same backbone and side-chains but different positions of the nitrogen atoms in the thiazole units. This subtle change significantly influences their optoelectronic, molecular packing, and charge-transport properties. P2 with a greater backbone torsion has favorable edge-on orientations and a high electron mobility μ_e of 2.55 cm²  V^-1  s^-1 . Moreover, P2-based transistors show an excellent shelf-storage stability in air even after the storage for 1 month.

Spontaneous Doping at the Polymer-Polymer Interface for High-Performance Organic Transistors

Low- k amorphous fluorinated polymers such as poly(perfluoroalkenylvinyl ether) (CYTOP) have widely been used as gate dielectrics for organic field-effect transistors (OFETs) because of their strong hydrophobicity to prevent the penetration of moisture and other contaminants and their perfect solvent orthogonality with organic semiconductors. Here, we report a new functionality of the fluorinated low- k polymer dielectrics, which is spontaneous p doping at the dielectric-semiconductor interface in OFETs. This functionality makes the ambipolar charge transport a unipolar p type. In the OFETs based on indacenodithiophene- co-benzothiadiazole and diketopyrrolopyrrole-thieno[3,2- b]thiophene, the charge transport is obviously ambipolar when paired with common polymer dielectrics such as poly(methyl methacrylate); however, it is perfectly modulated to the unipolar p type by applying the fluorinated dielectrics of CYTOP and poly(tetrafluoroethylene) (Teflon). We propose that this modulation of charge transport results from the rearrangement of C-F bonds at the interface between the fluorine-containing dielectrics and the conjugated polymer semiconductors by proper thermal annealing. These well-aligned dipole moments lead to an abrupt downshift of the Fermi level of the semiconductor toward the highest occupied molecular orbitals near the dielectric-semiconductor interface, which provides a p-doping effect on the channel transport and results in unipolar p-type characteristics in the composed OFETs. This study reveals a new functionality of the fluorinated dielectrics for future organic electronics.

Fine Structural Tuning of Thieno[3,2- b] Pyrrole Donor for Designing Banana-Shaped Semiconductors Relevant to Organic Field Effect Transistors

On the basis of the newly synthesized banana-shaped thieno[3,2- b] pyrrole building block [Bulumulla, C.; Gunawardhana, R.; Kularatne, R. N.; Hill, M. E.; McCandless, G. T.; Biewer, M. C.; Stefan, M. C. Thieno[3,2- b] pyrrole-Benzothiadiazole Banana-Shaped Small Molecules for Organic Field Effect Transistors. ACS Appl. Mater. Interfaces 2018, 10, 11818-11825], several small molecules that can be used as organic semiconducting materials were theoretically designed. We have shown that these novel molecules with the donor-π conjugated bridge-acceptor-π conjugated bridge-donor (D-π-A-π-D) building block exhibit superior charge transport properties in organic field-effect transistors (OFETs). A variety of donors, π-bridges, and acceptors are examined, and the structural, electronic, optical, and charge transport properties of designed semiconductors are systematically investigated. The results highlight the impact of the core acceptor in improving the transport properties of the designed molecules. In particular, this work points toward the benzo-bis(1,2,5-thiadiazole) as the most promising acceptor that can be combined with thiophene π-bridge and flanked benzo-thiadiazole terminal units to produce a reasonable candidate for synthesis and for incorporating into OFET materials. For the suggested semiconductor, the small electron reorganization energy and large intramolecular coupling originating from dense π-stacking gave rise to enhanced electron mobility. This strategy can be helpful for further improving the performance of curved small molecules in field-effect devices.

Synthesis of conjugated polymers using aryl-bromides via Cu-catalyzed direct arylation polymerization (Cu-DArP)

The first report on direct arylation polymerization with copper catalysts and aryl-bromide monomers expands the sustainability and practicality of DArP.

New Fused Pyrrolopyridine-Based Copolymers for Organic Solar Cell

A fused pyrrolopyridine core having substituents on the nitrogen atom instead of the carbon atom of the indoloindole unit is developed as a new donor unit for organic electronics. The new donor-acceptor copolymers, PDHPHBT, PDHPFBT, and PDHP2FBT, are synthesized using the new donor unit, well-known benzothiadiazole derivatives containing fluorine atoms as the acceptor. The thermal, optical, and electrochemical properties of these novel copolymers are reported. A solar cell using PDHPFBT with diphenyl ether has an open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of 0.86 V, 11.32 mA cm^-2 , 0.59%, and 5.68%, respectively, under AM 1.5G illumination (100 mW cm^-2 ) in the absence of annealing.

Copolymers of Bis-Diketopyrrolopyrrole and Benzothiadiazole Derivatives for High-Performance Ambipolar Field-Effect Transistors on Flexible Substrates

We develop an "acceptor dimerization" strategy by a bis-diketopyrrolopyrrole (2DPP) for an ambipolar organic semiconductor. Copolymers of 2DPP and benzothiadiazole (BTz) derivatives, P2DPP-BTz and P2DPP-2FBTz, are designed and synthesized. Both of the polymers exhibit narrow optical bandgaps of ca. 1.30 eV. The strong electron-withdrawing property of 2DPP results in low-lying lowest unoccupied molecular orbital (LUMO) energy levels of the polymers, improving the electron mobilities. 2D grazing incident X-ray diffraction and atomic force microscopy indicate that the P2DPP-BTz exhibits a small π-π stacking distance of 3.59 Å and a smooth interface, thus promoting high mobility. To take full advantage of the flexibility of organic semiconductors, flexible field-effect transistors (FETs) were fabricated on poly(ethylene terephthalate) (PET) substrates. The FETs based on P2DPP-BTz show high performance with hole and electron mobilities of 1.73 and 2.58 cm² V^-1 s^-1, respectively. Our results demonstrate that the 2DPP acceptor is a promising building block for high-mobility ambipolar polymers.

Thiazole Imide-Based All-Acceptor Homopolymer: Achieving High-Performance Unipolar Electron Transport in Organic Thin-Film Transistors

High-performance unipolar n-type polymer semiconductors are critical for advancing the field of organic electronics, which relies on the design and synthesis of new electron-deficient building blocks with good solubilizing capability, favorable geometry, and optimized electrical properties. Herein, two novel imide-functionalized thiazoles, 5,5'-bithiazole-4,4'-dicarboxyimide (BTzI) and 2,2'-bithiazolothienyl-4,4',10,10'-tetracarboxydiimide (DTzTI), are successfully synthesized. Single crystal analysis and physicochemical study reveal that DTzTI is an excellent building block for constructing all-acceptor homopolymers, and the resulting polymer poly(2,2'-bithiazolothienyl-4,4',10,10'-tetracarboxydiimide) (PDTzTI) exhibits unipolar n-type transport with a remarkable electron mobility (μ_e ) of 1.61 cm² V^-1 s^-1 , low off-currents (I_off ) of 10^-10 -10^-11 A, and substantial current on/off ratios (I_on /I_off ) of 10⁷ -10⁸ in organic thin-film transistors. The all-acceptor homopolymer shows distinctive advantages over prevailing n-type donor-acceptor copolymers, which suffer from ambipolar transport with high I_off s > 10^-8 A and small I_on /I_off s < 10⁵ . The results demonstrate that the all-acceptor approach is superior to the donor-acceptor one, which results in unipolar electron transport with more ideal transistor performance characteristics.

Novel Conjugated Polymers Prepared by Direct (Hetero) arylation: An Eco-Friendly Tool for Organic Electronics

The phthalimide (PhI) moiety has been attracting more attention as an excellent acceptor building block in donor-acceptor (D-A) conjugated polymers. In this paper; three D-A conjugated polymers with or without thiocarbonyl moieties are successfully prepared by the direct (hetero)-arylation polymerization (DHAP), which is an atom efficient and facile synthetic strategy to obtain polymer materials. Compared with the traditional carbon-carbon coupling reactions, this method possesses more advantages, including: fewer synthetic steps, avoidance of the preparation of the organometallic reagents, higher atom economy and fewer toxic byproducts, better compatibility with chemically sensitive functional groups and so on. All three of these designed PhI-based polymers exhibited favourable optoelectronic and thermal performance. The optical, thermodynamic and electrochemical properties of the synthesized polymers were systematically investigated using ultraviolet-visible (UV-vis) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and cyclic voltammetry (CV). The results of these three polymers indicated that thionation of the carbonyl was a highly effective methods to improve the properties of PhI-based polymers; and provided impetus for the development of thionated PhI derivatives for organic electronic applications.

Copper catalyzed synthesis of conjugated copolymers using direct arylation polymerization

As an effort to replace palladium catalysts, we report the first example of a Copper-catalyzed Direct Arylation Polymerization (DArP).

Proton triggered emission and selective sensing of 2,4,6-trinitrophenol using a fluorescent hydrosol of 2-phenylquinoline

Compound 2-phenylquinoline (PhQ) displayed novel aggregation induced emission enhancement (AIEE) characteristics in its aggregate/solid state. It allows reversible fluorescence switching in acidic and basic media and ‘turn off’ fluorescence sensor for TNP.

A one-pot strategy to improve end-capping efficacy in Stille poly-condensations

A reproducible synthetic method affording end-functionalized conjugated polymers via Stille polycondensations based upon end-capping reagent relative kinetics is presented.

trans-A2B-corrole bearing 2,3-di(2-pyridyl)quinoxaline (DPQ)/phenothiazine moieties: synthesis, characterization, electrochemistry and photophysics

Singlet–singlet energy transfer and electron transfer processes in corrole–phenothiazine and corrole–DPQ dyads were demonstrated by using electrochemical and fluorescence (steady-state and time-resolved) spectral studies.

Organic photovoltaics of diketopyrrolopyrrole copolymers with unsymmetric and regiorandom configuration of the side units

Diketopyrrolopyrrole (DPP) is a representative electron acceptor incorporated into narrow-bandgap polymers for organic photovoltaic cells (OPV). Commonly, identical aromatic units are attached to the sides of the DPP unit, forming symmetric DPP polymers. Herein we report the synthesis and characterization of DPP copolymers consisting of unsymmetric configurations of the side aromatics. The unsymmetric DPP copolymer with thienothiophene and benzene side moieties exhibits good solubility owing to the twisted dihedral angle at benzene and regiorandom configuration. A significant shallowing of the highest occupied molecular orbital level is observed in accordance with the electron-donating nature of the side units (benzene, thiophene, and thienothiophene). The overall power conversion efficiencies of the unsymmetric DPPs (2.3–2.4%) are greater than that of the centrosymmetric analogue (0.45%), which is discussed in view of bulk heterojunction morphology, polymer crystallinity, and space-charge-limited current mobilities. This comparative study highlights the effect of unsymmetric design on the molecular stacking and OPV performance of DPP copolymers.

Diketopyrrolopyrroles with unsymmetric side aromatics of benzene and (thiophene or thienothiophene) were copolymerized with 2-dimensional benzodithiophene, and their solar cell devices were characterized.

Toward Environmentally Robust Organic Electronics: Approaches and Applications

Recent interest in flexible electronics has led to a paradigm shift in consumer electronics, and the emergent development of stretchable and wearable electronics is opening a new spectrum of ubiquitous applications for electronics. Organic electronic materials, such as π-conjugated small molecules and polymers, are highly suitable for use in low-cost wearable electronic devices, and their charge-carrier mobilities have now exceeded that of amorphous silicon. However, their commercialization is minimal, mainly because of weaknesses in terms of operational stability, long-term stability under ambient conditions, and chemical stability related to fabrication processes. Recently, however, many attempts have been made to overcome such instabilities of organic electronic materials. Here, an overview is provided of the strategies developed for environmentally robust organic electronics to overcome the detrimental effects of various critical factors such as oxygen, water, chemicals, heat, and light. Additionally, molecular design approaches to π-conjugated small molecules and polymers that are highly stable under ambient and harsh conditions are explored; such materials will circumvent the need for encapsulation and provide a greater degree of freedom using simple solution-based device-fabrication techniques. Applications that are made possible through these strategies are highlighted.

Naphthobischalcogenadiazole Conjugated Polymers: Emerging Materials for Organic Electronics

π-Conjugated polymers are an important class of materials for organic electronics. In the past decade, numerous polymers with donor-acceptor molecular structures have been developed and used as the active materials for organic devices, such as organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). The choice of the building unit is the primary step for designing the polymers. Benzochalcogenadiazoles (BXzs) are one of the most familiar acceptor building units studied in this area. As their doubly fused system, naphthobischalcogenadiazoles (NXzs), i.e., naphthobisthiadiazole (NTz), naphthobisoxadiazole (NOz), and naphthobisselenadiazole (NSz) are emerging building units that provide interesting electronic properties and highly self-assembling nature for π-conjugated polymers. With these fruitful features, π-conjugated polymers based on these building units demonstrate great performances in OFETs and OPVs. In particular, in OPVs, NTz-based polymers have exhibited more than 10% efficiency, which is among the highest values reported so far. In this Progress Report, the synthesis, properties, and structures of NXzs and their polymers is summarized. The device performance is also highlighted and the structure-property relationships of the polymers are discussed.

Hole Mobility and Electron Injection Properties of D-A Conjugated Copolymers with Fluorinated Phenylene Acceptor Units

A novel wide-gap conjugated polymer PhF2,5 (E_g = 1.9 eV) is designed to contain alternating cyclopentadithiophene and difluorophenylene unit with the goal of favoring unipolar organic field effect transistor characteristics. The higher lowest unoccupied molecular orbital energy of PhF2,5 increases the barrier to electron injection, leading to unipolar transport and higher on/off ratios, without sacrificing desirable high hole mobilities.

Synthesis of diketopyrrolopyrrole based conjugated polymers containing thieno[3,2-b]thiophene flanking groups for high performance thin film transistors

New D–A conjugate polymers based on 3,6-bis(2-bromothieno-[3,2-b]thiophen-5-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]-pyrrole-1,4-(2H,5H)-dione combined with bithiophene, di(2-thienyl)ethene, and di(selenophene-2-yl)ethene were synthesized.

A spiro-centered thermopolymerizable fluorinated macromonomer: synthesis and conversion to the high performance polymer

A new spiro-centered thermopolymerizable fluorinated macromonomer is reported here.