Solution-Processable Star-Shaped Molecules with Triphenylamine Core and Dicyanovinyl Endgroups for Organic Solar Cells

Two new star-shaped D-pi-A molecules with triphenylamine (TPA) as core and donor unit, dicyanovinyl (DCN) as end group and acceptor unit, and 4,4'-dihexyl-2,2'-bithiophene (bT) or 4, 4'-dihexyl-2,2'-bithiophene vinylene (bTV) as pi bridge, S(TPA-bT-DCN) and S(TPA-bTV-DCN), were synthesized for the application as donor materials in solution-processed bulk-heterojunction organic solar cells (OSCs). The two compounds are soluble in common organic solvents, because of the three-dimensional structure of the TPA unit and the two hexyl side chains on the bithiophene unit. S(TPA-bTV-DCN) film shows a broad absorption band from 360 to 750 nm. Absorption edge of S(TPA-bTV-DCN) film is red-shifted by ca. 78 nm than that of S(TPA-bT-DCN) film, benefitted from the vinylene bridges between TPA and bithiophene units in S(TPA-bTV-DCN). Power conversion efficiency (PCE) of the solution-processed bulk-heterojunction OSC based on a blend of S(TPA-bTV-DCN) and [6,6]-phenyl-C-71-butyric acid methyl ester (1:2, w/w) reached 3.0% with a short circuit current density of 7.76 mA/cm(2) and an open circuit voltage of 0.88 V, under the illumination of AM.1.5, 100 mW/cm(2). In comparison, PCE of the OSC based on S(TPA-bT-DCN) as donor is 1.4% under the same experimental conditions. The PCE of 3.0% for S(TPA-bTV-DCN) is among the top values for the solution-processed molecule-based OSCs reported so far.