Ling Ai

Synthesis, crystal structure, and polymerization of butterfly-shaped thieno[3,2-b]thiophene oligomers

A series of new butterfly-shaped thieno[3,2-b]thiophene oligomers with phenyl and thiophene units were synthesized through Suzuki coupling and Stille coupling reactions. The optical and thermal properties of these materials can be tuned by varying both substituents and the conjugation length. The crystal structures have been determined and showed a syn- or anticlinal conformation in the crystal of molecule 4. The electronic properties of the monomers and their electropolymerization ability are discussed and rationalized as a function of their molecular structure. Moreover, stable cross-linked conjugated polymers were formed by electropolymerization.

Anthradithiophene-benzothiadiazole-based small molecule donors for organic solar cells

A new A–D–A small molecule involving anthradithiophene as a donor and benzothiadiazole as an acceptor unit has been synthesized by Stille coupling reaction. Its thermal, optical and electronic properties, hole mobility and photovoltaic properties have been fully characterized. The resulting material shows a broad absorption range (300–750 nm), a low band gap (1.59 eV) and a moderate hole mobility (8.81 × 10−4 cm2 V−1 s−1). We used the new small molecule blended with PC71BM as the active layer to fabricate solution-processed organic solar cells (OSCs), and employed a variety of post-treatment methods to optimize the device performance. With the help of polar solvent exposure, the highest power conversion efficiency (PCE) of 0.55% was obtained. These results would supply useful information to understand the relationship between molecular structure and photovoltaic properties of anthradithiophene/benzothiadiazole-based OSCs.

Highly efficient polymer solar cells using a non-conjugated small-molecule zwitterion with enhancement of electron transfer and collection

A novel non-conjugated small-molecule zwitterion is developed as a cathode interfacial material to enhance the electron transfer and collection properties of high-performance PSCs. The devices show significantly increased performance with power conversion efficiencies up to 9.51%. It is noteworthy that the results here provide significant scientific insights into further improvement of interfacial modification and performance of polymer solar cells.

Stable organic field-effect-transistors with high mobilities unaffected by supporting dielectric based on phenylene-bridged thienobenzothiophene

We report on the electrical properties of organic field-effect transistors (OFET) based on a new class of organic semiconductors. The molecules consist of the same thieno[2,3-b][1]benzothiophene building blocks, connected by different π-bridge spacers (ethylene, phenylene, and fluorophenylene). Molecular orbitals and highest occupied molecular orbital/lowest unoccupied molecular orbital energies were calculated and compared with results from cyclic voltammetric and UV-vis absorption measurements. In order to study the influence of the bridge groups on the molecular arrangement and surface interaction, the transistor performance on a wide range of dielectrics has been investigated in detail. These include as grown SiO2 and Al2O3 and also treated with octadecyltrichrolosilane and octadecylphosphonic acid, as well as Cytop and Parylene C. An extended study of the multitude of combinations of these materials revealed mobilities up to ∼1 cm2/Vs, measured for devices made of the phenylene-bridged compound. Surprisingly, the mobility was quite independent of the supporting gate dielectric. Stability over time has been observed with no degradation after 5 months. By eliminating the hysteresis using Cytop, we were able to show that some of the molecules form films without long-term charge carrier trapping. These are interesting features for practical industrial processing of organic electronics.

Enhanced high-open circuit voltage in fluorinated benzoselenadiazole-based polymer solar cells

Three new donor–acceptor copolymers (PCDTBSe, PCDTFBSe, and PCDTDFBSe) were designed and synthesized with 2,7-carbazole as the donor (D) unit and benzoselenadiazole (BSe), monofluoro-benzoselenadiazole, and difluoro-benzoselenadiazole as the acceptor (A) units, respectively. The structure–property relationship of these polymers was elucidated in bulk heterojunction polymer solar cells. All the polymers were fully characterized and exhibited good thermal stability and broad absorption. The highest occupied molecular orbitals (HOMOs) of the PCDTBSe (−5.29 eV), PCDTFBSe (−5.32 eV), and PCDTDFBSe (−5.35 eV) were decreased by incorporating fluorine atoms on the polymer backbone. The low-lying HOMO energy level suggested that the polymers would exhibit high open circuit voltage (V OC) when blended with fullerene as the electron acceptor. Solar cell based on PCDTFBSe displayed a power conversion efficiency of 1.09% with a short-circuit current density (JSC) of 4.29 mA cm−2, a VOC of 0.78 V, and a fill factor (FF) of 32.51%, under the illumination of AM1.5G, 100 mW cm−2.

Benzothieno[2,3-b]thiophene semiconductors: synthesis, characterization and applications in organic field-effect transistors

An efficient synthetic approach to a series of benzothieno[2,3-b]thiophene (BTT) derivatives used as an important core with different bridge spacers is described. Thermal properties of the present compounds are stable: neither phase transition nor thermal decomposition was observed up to 300 °C. The adjacent molecule crystal stackings are shifted affording a nearly 1/3 intermolecular π-overlap. The OFETs based on BTTB exhibit excellent field-effect performances with a mobility of 0.46 cm2 V−1 s−1 and on–off current ratios larger than 107 at room temperature. All the results demonstrate these benzothieno[2,3-b]thiophene derivatives as promising materials for optoelectronic devices.

CCDC 915957: Experimental Crystal Structure Determination

Related Article: Ying Liu, Yang Wang, Ling Ai, Zhiyang Liu, Xinhua Ouyang, Ziyi Ge|2015|Dyes Pigm.|121|363|doi:10.1016/j.dyepig.2015.05.032