Exploitation Of New Electron-Accepting Materials With A Large π-conjugated Structure For Organic Solar Cells

Recently, organic solar cells (OSCs) have become one of the research hot topics due to their advantages in chemical structural diversity, solution-processability and flexibility, over the traditional the Si-based solar cells. In general, the active layer of OSCs is composed of electron-donating and accepting materials. In the past ten years, a variety of excellent novel electron-donating materials have been developed. However, little progress has been achieved for electron-accepting materials. Although they are expensive and hard to synthesize, fullerene derivatives are the main choice for the accepting materials. Aiming at the exploration of novel non-fullerene electron-accepting materials, this thesis focuses on the design and synthesis of small molecular compounds with a largeπ-conjugated structure and electron-deficient nature. Furthermore, by modifying side chains of the compounds, their solubility and packing structure in solid state have been finely tuned toward the favor of charge carriers transportation. In addition, we have also developed a kind of electron-deficient conjugated polymer, which can be used as fluorescent sensor to detect some specific metal ions. The main contents are as listed as follows:1. Perylene diimide (PDI) derivatives are a kind of electron-accepting materials with a large p-conjugated structure. But their wide applications are limited to their poor solubility and unfavorable packing structure. In this work, a series of alkyl oligoethylene glycol chains having different length have been integrated into both the four bay positions and two N-sites of a PDI core, affording high soluble PDI compounds. Some of these compounds exhibit liquid crystalline properties, which have ordered packing structure in solid state. Finally, these compounds had been utilized to fabricate field-effect transistor devices and investigated the charge carrier transportation properties.2. A new hexaazatrinaphthylene (HATNA) derivative has been designed. Compared with the general HATNA derivatives, the designed compound has a largerπ-conjugated structure and four potential binding sites for metal ions. Through intermolecularπ-πinteraction and metal-ligand coordination, its liquid crystalline and charge-transportation properties are expected to be finely tuned. In order to improve its solubility, six alkyl chains have been attached to the side of the discotic aromatic ring. However, the synthesis has met problems in the final ring-closing step, which needs a more efficient intramolecular coupling reaction. Although the ultimate goal has not been achieved, an intermediate product with strong fluorescent properties provides an idea for the third part work.3. Based on the second work above, a alternating conjugated copolymer composed of benzothiadiazole and pyridine, both electron-deficient, has been designed and synthesized. Because the side chains of the polymer are hydrophilic oligo(ethylene glycol)s, the polymer is partially soluble in water, but entirely soluble in THF. Fluorescence spectroscopy revealed a strong fluorescence of the polymer in THF/water mixed solvent. Of more importance, obvious fluorescence-quenching have been observed when the polymer solution was titrated with Fe²⁺, Fe³⁺, Co²⁺, and Cu²⁺. Especially, Cu²⁺ shows a specific large quenching efficiency. In contrast, no fluorescence quenching was observed with Na⁺, K⁺, Mg²⁺, et al. These results indicate that the polymer can be used as a fluorescent sensor ,which has certain selectivity toward metal ions. Moreover, the electron-deficient structure may be in favor of the application of this copolymer in OSCs field.