Benzo[1,2-b :4,5-b ′]dithiophene Building Block for the Synthesis of Semiconducting Polymers

Design, Synthesis, and Theoretical Studies on the Benzoxadiazole and Thienopyrrole Containing Conjugated Random Copolymers for Organic Solar Cell Applications

In this study, six different donor-π-acceptor1-π-donor-acceptor2 type random co-polymers containing benzodithiophene as a donor, benzooxadiazole (BO), and thieno[3,4-c]pyrrole-4,6-dione (TPD) as acceptor, have been synthesized and characterized. In addition to the acceptor core ratio at different values, the effect of aromatic bridge structures on the optical, electronic, and photovoltaic properties of six different random co-polymers is investigated by using thiophene and selenophene structures as aromatic bridge units. To investigate how the acceptor unit ratio and replacement of aromatic bridge units impact the structural, electronic, and optical properties of the polymers, density functional theory (DFT) calculations are carried out for the tetramer models. The open-circuit voltage (VOC), which is strongly correlated with the HOMO levels of the donor material, is enhanced with the increasing ratio of the TPD moiety. On the other hand, the short-circuit current (JSC), which is associated with the absorption ability of the donor material, is improved by the increasing ratio of BO moiety with the π-bridges. BO moiety dominant selenophene π-bridged co-polymer (P4) showed the best performance with a power conversion efficiency (PCE) of 6.26%, a JSC of 11.44 mA cm2, a VOC of 0.80 V, and a fill factor (FF) of 68.81%.

A New Noncovalently Fused-Ring Electron Acceptor Based on 3,7-Dialkyloxybenzo[1,2-b:4,5-b']dithiophene for Low-Cost and High-Performance Organic Solar Cells

The innovation of high-performance fused-ring electron acceptors (FREAs) has carried the field of organic solar cells (OSCs) towards a new stage of development. However, due to high synthetic complexity and production costs, FREAs may be not the most promising candidates for future commercialization applications. To address these disadvantages of FREAs, a series of low-cost acceptors, named as noncovalently fused-ring electron acceptors (NFREAs), has been successfully constructed by employing the strategy of noncovalently conformational locks (NoCLs). Herein, a novel NFREA (BDTO-4F) based on 3,7-dialkyloxybenzo[1,2-b:4,5-b']dithiophene is synthesized and fully characterized. Benefiting from the complementary absorption of the donor and acceptor, balanced charge transport, and favorable film morphology, J52:BDTO-4F based OSCs afforded a satisfied power conversion efficiency (PCE) of 12.09%, much higher than PBDB-T:BDTO-4F-based devices (8.30%). It is worth mentioning that BDTO-4F possesses a higher figure-of-merit (FOM) value of 55.65 in comparison with several representative FREAs based on a cost-efficiency evaluation. This work demonstrates the potential of the novel BDT derivative for constructing low-cost and high-performance NFREAs, providing a valuable insight on the materials design. This article is protected by copyright. All rights reserved.

Dithieno[3,2-b:2',3'-d]arsole-containing conjugated polymers in organic photovoltaic devices

Arsole-derived conjugated polymers are a relatively new class of materials in the field of organic electronics. Herein, we report the synthesis of two new donor polymers containing fused dithieno[3,2-b:2',3'-d]arsole units and report their application in bulk heterojunction solar cells for the first time. Devices based upon blends with PC₇₁BM display high open circuit voltages around 0.9 V and demonstrate power conversion efficiencies around 4%.

Recent Advances in n-Type Polymers for All-Polymer Solar Cells

All-polymer solar cells (all-PSCs) based on n- and p-type polymers have emerged as promising alternatives to fullerene-based solar cells due to their unique advantages such as good chemical and electronic adjustability, and better thermal and photochemical stabilities. Rapid advances have been made in the development of n-type polymers consisting of various electron acceptor units for all-PSCs. So far, more than 200 n-type polymer acceptors have been reported. In the last seven years, the power conversion efficiency (PCE) of all-PSCs rapidly increased and has now surpassed 10%, meaning they are approaching the performance of state-of-the-art solar cells using fullerene derivatives as acceptors. This review discusses the design criteria, synthesis, and structure-property relationships of n-type polymers that have been used in all-PSCs. Additionally, it highlights the recent progress toward photovoltaic performance enhancement of binary, ternary, and tandem all-PSCs. Finally, the challenges and prospects for further development of all-PSCs are briefly considered.

Unmasking Dipole Character of Acyl Ketene Dithioacetals via a Cascade Reaction with Arynes: Synthesis of Benzo[b]thiophenes

An unusual strategy toward novel substituted benzo[b]thiophenes has been developed. The generation of arynes in the presence of acyl ketene dithioacetals resulted in a cascade reaction involving [3 + 2] cycloaddition, and a dealkylative arylation of a thioether moiety to afford 2,3-disubstuted benzo[b]thiophenes. This route represents an expeditious approach to benzothiophenes that employs acyl ketene dithioacetals as dipoles.

Rhodium-catalyzed dehydrogenative coupling of phenylheteroarenes with alkynes or alkenes

Benzo-fused tri- to heptacyclic heteroarenes were effectively constructed by the rhodium-catalyzed dehydrogenative coupling of phenylheteroarenes with alkynes. Using alkenes as coupling partners, dehydrogenative alkenylation took place selectively on the phenyl moiety of phenylheteroarenes. Several experiments with deuterium-labeled substrates indicated that double C-H bond cleavages take place even in the reaction with alkenes.

Pyrrolo[3,4-g]quinoxaline-6,8-dione-based conjugated copolymers for bulk heterojunction solar cells with high photovoltages

D–A copolymers incorporating new pyrrolo[3,4-g]quinoxaline-6,8-dione (PQD) building blocks were synthesized for bulk heterojunction solar cells with high photovoltages.

A new highly conjugated crossed benzodithiophene and its donor–acceptor copolymers for high open circuit voltages polymer solar cells

What is theV_oclimit of BDT and DTBT backboned photovoltaic polymers? At least 0.95 V can be achieved.!

2,6-Diphenyl- and -distyryl-capped 3,7-dialkoxybenzo[1,2-b:4,5-b']dithiophenes and their dithieno-annulated higher homologs: structural phase transition with enhanced charge carrier mobility

Synthesis of the title benzo[1,2-b:4,5-b']dithiophenes was achieved using 2-ethylhexyl 3,7-dihydroxybenzo[1,2-b:4,5-b']dithiophene-2,6-dicarboxylate as the common starting material. The effect of the introduction of phenyl and styryl groups as well as thieno-annulation to the benzo[1,2-b:4,5-b']dithiophene core on π-conjugation was estimated by means of absorption and emission spectrometry and cyclic voltammetry. The phase behaviours of the compounds were also observed by differential scanning calorimetry and the dithieno-annulated higher homologs were found to show a solid-solid (crystalline-crystalline) phase transition. Then, intrinsic charge carrier mobilities in the π-systems were measured by the flash-photolysis time-resolved microwave conductivity (FP-TRMC) method and the values were in the range of 0.04-0.17 cm(2) V(-1) s(-1). Remarkably, the thieno-annulated and phenyl-capped derivative showed a temperature/phase-dependent hole mobility profile with 3-fold increment in the second crystalline phase above 100 °C.

Oriented thin films of a benzodithiophene covalent organic framework

A mesoporous electron-donor covalent organic framework based on a benzodithiophene core, BDT-COF, was obtained through condensation of a benzodithiophene-containing diboronic acid and hexahydroxytriphenylene (HHTP). BDT-COF is a highly porous, crystalline, and thermally stable material, which can be handled in air. Highly porous, crystalline oriented thin BDT-COF films were synthesized from solution on different polycrystalline surfaces, indicating the generality of the synthetic strategy. The favorable orientation, crystallinity, porosity, and the growth mode of the thin BDT-COF films were studied by means of X-ray diffraction (XRD), 2D grazing incidence diffraction (GID), transmission and scanning electron microscopy (TEM, SEM), and krypton sorption. The highly porous thin BDT-COF films were infiltrated with soluble fullerene derivatives, such as [6,6]-phenyl C61 butyric acid methyl ester (PCBM), to obtain an interpenetrated electron-donor/acceptor host-guest system. Light-induced charge transfer from the BDT-framework to PCBM acceptor molecules was indicated by efficient photoluminescence quenching. Moreover, we monitored the dynamics of photogenerated hole-polarons via transient absorption spectroscopy. This work represents a combined study of the structural and optical properties of highly oriented mesoporous thin COF films serving as host for the generation of periodic interpenetrated electron-donor and electron-acceptor systems.

25th anniversary article: isoindigo-based polymers and small molecules for bulk heterojunction solar cells and field effect transistors

Driven by the potential advantages and promising applications of organic solar cells, donor-acceptor (D-A) polymers have been intensively investigated in the past years. One of the strong electron-withdrawing groups that were widely used as acceptors for the construction of D-A polymers for applications in polymer solar cells and FETs is isoindigo. The isoindigo-based polymer solar cells have reached efficiencies up to ∼7% and hole mobilities as high as 3.62 cm(2) V(-1) s(-1) have been realized by FETs based on isoindigo polymers. Over one hundred isoindigo-based small molecules and polymers have been developed in only three years. This review is an attempt to summarize the structures and properties of the isoindigo-based polymers and small molecules that have been reported in the literature since their inception in 2010. Focus has been given only to the syntheses and device performances of those polymers and small molecules that were designed for use in solar cells and FETs. Attempt has been made to deduce structure-property relationships that would guide the design of isoindigo-based materials. It is expected that this review will present useful guidelines for the design of efficient isoindigo-based materials for applications in solar cells and FETs.

A non-photochemical route to synthesize simple benzo[1,2-b:4,3-b′]dithiophenes: FeCl3-mediated cyclization of dithienyl ethenes

The FeCl₃-mediated cyclization of α,α′-disubstituted Z-alkenes as a general and non-photochemical route to synthesize benzo[1,2-b:4,3-b′]dithiophene derivatives.

Rational design on D–A conjugated P(BDT–DTBT) polymers for polymer solar cells

This review summarizes the various structural modifications and photovoltaic properties of the benzodithiophene–benzothiadiazole conjugated polymers [P(BDT–DTBT)] and their derivatives.

Rhodium-catalyzed annulative coupling of 3-phenylthiophenes with alkynes involving double C-H bond cleavages

Double CH bond activation took place efficiently upon treatment of 3-phenylthiophenes with alkynes in the presence of a rhodium catalyst and a copper salt oxidant to form the corresponding naphthothiophene derivatives. Dehydrogenative coupling with alkenes was also found to occur on the phenyl moiety rather than the thiophene ring. These reactions provide straightforward synthetic methods for π-conjugated molecules involving a thiophene unit from readily available, simple building blocks.

Fullerene nanoarchitectonics: from zero to higher dimensions

The strategic design of nanostructured materials, the properties of which could be controlled across different length scales and which, at the same time, could be used as building blocks for the construction of devices and functional systems into new technological platforms that are based on sustainable processes, is an important issue in bottom-up nanotechnology.Such strategic design has enabled the fabrication of materials by using convergent bottom-up and top-down strategies. Recent developments in the assembly of functional fullerene (C60) molecules, either in bulk or at interfaces, have allowed the production of shape-controlled nano-to-microsized objects that possess excellent optoelectronic properties, thus enabling the fabrication of optoelectronic devices. Because fullerene molecules can be regarded as an ideal zero-dimensional (0D) building units with attractive functions, the construction of higher-dimensional objects, that is, 1D, 2D, and 3D nanomaterials may realize important aspects of nanoarchitectonics. This Focus Review summarizes the recent developments in the production of nanostructured fullerenes and techniques for the elaboration of fullerene nanomaterials into hierarchic structures.

Solution-processed and air-stable n-type organic thin-film transistors based on thiophene-fused dicyanoquinonediimine (DCNQI) deriatives

π-Conjugated systems 2a and 2b containing thiophene-fused DCNQI with long alkyl and trifluoromethylphenyl groups were synthesized as potential active materials for solution-processed and air-stable n-type organic thin-film transistors (OTFTs). The electrochemical measurements revealed that the lowest unoccupied molecular orbital (LUMO) of the compounds have an energy level less than -4.0 eV, indicating air stable n-type materials. The long alkyl groups endowed the compounds good solubility and solution-processability. X-ray diffraction measurements revealed the difference of the molecular arrangement depending on the alkyl groups, which were also observed in the UV-vis absorptions of the films. A relatively good mobility up to 0.003 cm(2) V(-1) s(-1) for 2a by spin-coating was obtained with good air stability.