Most small conjugated molecules applied in solar cells have linear structures containing multiple aromatic groups connected in series. However, unfavorable film forming ability and grain boundaries both originated from high crystallinity of linear small molecules are detrimental to device performances. As a result, 3-D structures, breakwater-like tetrapods are especially interesting owing to their unique ability to mutually interlock, which prevents dislodging and provides high structural stabilities. Herein, we report the synthesis and characterization of two tetrapodal breakwater-like small molecules, SO and SFBTD, as shown below.[1] Absorption, X-ray scattering and differential scanning calorimetry experiments indicate crystalline nature of these compounds but slow crystallization kinetics. Solar cells employing SO or SFBTD and phenyl-C61-butyric acid methyl ester (PCBM) were fabricated and evaluated. Relatively low performance was obtained mainly due to the lack of appropriate phase separation, which was caused by molecularly mixed blends with PCBM. The molecularly mixed blends is the result of slow crystallization feature of SO and SFBTD, which may be intrinsically resulted from the structure of each of its arms (SO) and also its tetrahedral geometry (SFBTD). Addition of low bandgap highly crystalline conjugated polymer poly(thienylene vinylene) (PTV) into the SO/PCBM blend was found to induce appreciable phase separation. Such ternary blend devices showed cooperatively improved performances over binary devices employing either SO or PTV alone. Our findings can give useful insight on the structure-property relationships of such 3-D small molecules and their applications in organic solar cells. Reference: [1] Yang, J. Z.; He, W. H.; Denman, K.; Jiang, Y. B. and Qin, Y. J. Mater. Chem. A 2015, 3, 2108

Molecular breakwater-like tetrapods for organic solar cells

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.