A vinylene‐linked benzo[1,2‐ b :4,5‐ b' ]dithiophene‐2,1,3‐benzothiadiazole low‐bandgap polymer

Research progress and application of high efficiency organic solar cells based on benzodithiophene donor materials

In recent decades, the demand for clean and renewable energy has grown increasingly urgent due to the irreversible alteration of the global climate change. As a result, organic solar cells (OSCs) have emerged as a promising alternative to address this issue. In this review, we summarize the recent progress in the molecular design strategies of benzodithiophene (BDT)-based polymer and small molecule donor materials since their birth, focusing on the development of main-chain engineering, side-chain engineering and other unique molecular design paths. Up to now, the state-of-the-art power conversion efficiency (PCE) of binary OSCs prepared by BDT-based donor materials has approached 20%. This work discusses the potential relationship between the molecular changes of donor materials and photoelectric performance in corresponding OSC devices in detail, thereby presenting a rational molecular design guidance for stable and efficient donor materials in future.

Rational Design of Low-Band Gap Star-Shaped Molecules With 2,4,6-Triphenyl-1,3,5-triazine as Core and Diketopyrrolopyrrole Derivatives as Arms for Organic Solar Cells Applications

A series of D-A novel star-shaped molecules with 2,4,6-triphenyl-1,3,5-triazine (TPTA) as core, diketopyrrolo[3,4-c]pyrrole (DPP) derivatives as arms, and triphenylamine (TPA) derivatives as end groups have been systematically investigated for organic solar cells (OSCs) applications. The electronic, optical, and charge transport properties were studied using density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches. The parameters such as energetic driving force ΔE L-L, adiabatic ionization potential AIP, and adiabatic electron affinity AEA were also calculated at the same level. The calculated results show that the introduction of different groups to the side of DPP backbones in the star-shaped molecules can tune the frontier molecular orbitals (FMOs) energy of the designed molecules. The designed molecules can provide match well with those of typical acceptors PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) and PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester). Additionally, the absorption wavelengths of the designed molecules show bathochromic shifts compared with that of the original molecule, respectively. The introduction of different groups can extend the absorption spectrum toward longer wavelengths, which is beneficial to harvest more sunlight. The calculated reorganization energies suggest that the designed molecules are expected to be the promising candidates for ambipolar charge transport materials except molecule with benzo[c]isothiazole group can be used as hole and electron transport material. Moreover, the different substituent groups do not significantly affect the stability of the designed molecules.

Dicyanobenzothiadiazole Derivatives Possessing Switchable Dielectric Permittivities

Benzothiadiazoles are important electron acceptors and are frequently employed as electron-deficient components of donor-acceptor polymers. We report the effect of nitrile functionalities on the reactivity, steric hindrance, optoelectronic properties, and dielectric permittivity in dicyanobenzothioadiazole (DCNBT). Dielectric spectroscopy in the bulk and in solution assisted by DFT-calculations revealed that these molecules can be engineered to engender maximum values of the dipole moment and of dielectric permittivity due to the strong electron-withdrawing effect of the nitrile groups. The self-assembly in the bulk was investigated by X-ray scattering performed on single crystals, fibers (2D-WAXS), and thin films (GiWAXS). Combining these results, we found a switching of dielectric permittivity of the 4,7-alkylthienyl-substituted dicyanobenzothiadiazole at the transition from the liquid crystalline to the isotropic phase with values capable of competing with the best known rodlike liquid crystals.

Vinylene-Linked Oligothiophene-Difluorobenzothiadiazole Copolymer for Transistor Applications

The synthesis of the novel donor-acceptor monomer 4,7-bis[(E)-2-(5-bromo-3-dodecylylthiophen-2-yl)ethenyl]-5,6-difluoro-2,1,3-benzothiadiazole (FBT-V2T2) is reported. Polymerization with 4,4'-ditetradecyl-5,5'-bistrimethylstannyl-2,2'-bithiophene afforded a highly crystalline polymer that aggregated strongly in solution. Polymer films were well ordered resulting in high performance field-effect transistors with low onset voltages, negligible hysteresis, high channel current on/off ratios, and peak hole mobilities of up to 0.5 cm² V^-1 s^-1. Notably the transistors exhibited close to ideal behavior with extracted mobilities almost independent of gate of voltage.

A versatile and efficient synthesis of bithiophene-based dicarboxaldehydes from a common synthon

The efficient synthesis of several bithiophene dialdehydes from a common intermediate is reported.

Tunable spectra and charge transfer process of benzodifurandione-based polymer by sulfur substitution

The ground state geometry, optical and charge transport properties of benzodifurandione-based PPV (BDPPV) have been studied with density functional theory methods.

Conjugated donor–acceptor copolymers derived from phenylenevinylene and trisubstituted pyridine units

Copolymers having intramolecular donor–acceptor systems encompassing trisubstituted pyridine derivatives as acceptor and phenylenevinylene (PPV) unit as a donor segment were synthesized. In addition, thiophene-containing random terpolymer PPVPYT via palladium-catalyzing Heck coupling reaction is reported. The novel-substituted pyridine monomers (PYBr) are synthesized by adopting a one-pot synthesis method using p-toluenesulfonic acid as catalyst in ethanol medium, which results in an excellent yield of about 95%. All the copolymers Poly phenylenevinylene-co-Pyridine derivatives (PPVPY) and terpolymers of Polyphenylenevinylene-co-Pyridine and Thiophene (PPVPYT) are found to be soluble in organic solvents, such as tetrahydrofuran, chloroform, and N, N-dimethylformamide. The molecular weights of the synthesized polymers were characterized by gel permeation chromatography (GPC), and their chemical structures were confirmed by infra red and nuclear magnetic resonance spectroscopies. The electrochemical band gaps of PPVPY-1, PPVPY-2, and PPVPY-3 copolymers are estimated to be 2.55, 2.48, and 2.0, respectively. Similarly, the band gap of PPVPY75T25, PPVPY50T50, and PPVPY25T75 random copolymers are estimated as 2.31, 1.95, and 2.23, respectively. These polymers also show excellent optical and thermal properties.

Modeling of photoactive conjugated donor–acceptor copolymers: the effect of the exact HF exchange in DFT functionals on geometries and gap energies of oligomer and periodic models

Commonly used density functionals including an optimally tuned OT-ωB97X functional are benchmarked on oligomer and periodic models of donor–acceptor copolymers.

Integration of a silk fibroin based film as a luminescent down-shifting layer in ITO-free organic solar cells

A bio-derived silk-fibroin film doped with a luminescent dye and its application as luminescent down-shifting layer in organic solar cells.

Synthetic Aspects and Electro-Optical Properties of Fluorinated Arylenevinylenes for Luminescence and Photovoltaics

In this review, the main synthetic aspects and properties of fluorinated arylenevinylene compounds, both oligomers and polymers, are summarized and analyzed. Starting from vinyl organotin derivatives and aryl halides, the Stille cross-coupling reaction has been successfully applied as a versatile synthetic protocol to prepare a wide series of π-conjugated compounds, selectively fluorinated on the aromatic and/or vinylene units. The impact of fluoro-functionalization on properties, the solid state organization and intermolecular interactions of the synthesized compounds are discussed, also in comparison with the non-fluorinated counterparts. Luminescent and photovoltaic applications are also discussed, highlighting the role of fluorine on the performance of devices.