A solution-processable diketopyrrolopyrrole dye molecule with (fluoronaphthyl)thienyl endgroups for organic solar cells

A solution-processable dye molecule DPP(TFNa)(2) that consists of diketopyrrolopyrrole (DPP) as the core and 5-(6-fluoro-2-naphthyl)thienyl as the endgroups is presented for bulk heterojunction organic solar cells. DPP(TFNa)(2) is a crystalline solid with a T-m, of approximately 216 degrees C. X-ray diffraction experiments reveal that thermal annealing increases crystallinity of the as-cast film, thus beneficial to the absorption and charge-transport properties. DPP(TFNa)(2) exhibits two reversible one-electron oxidation waves at 0.87 and 1.16 V vs. Ag/AgCl reference electrode, respectively. Fitting the space-charge-limited current characteristics in a hole-only device results in a hole mobility of similar to 2.7 x 10(-4) cm(2) V-1 s(-1) at low voltages for DPP(TFNa)(2). A preliminary characterization of the solar cell (ITO/PEDOT:PSS/DPP(TFNa)(2):PC61BM/AI) yields a power conversion efficiency of approximately 3.0% under simulated AM 1.5G illumination (66.4 and 100 mW cm(-2), respectively). The fluorine effects on material properties such as morphology, absorption, electrochemistry, charge transport and the resulting device performance are discussed. (C) 2013 Elsevier Ltd. All rights reserved.