A Solution-Processable Dithienyldiketopyrrolopyrrole Dye Molecule with Acetylene as a π-Linkage for Organic Solar Cells

We present the efficient synthesis and photovoltaic response of a linearly conjugated molecule DT-DPP (AAnAT)2, which contains a dithienyldiketopyrrolopyrrole core symmetrically connected through a 9,10-anthracenyl unit to 3-alkylthiophene via an acetylene linkage. The compound is crystalline with a Tm of 204 °C. The as-cast film has a main broad absorption at 650 nm with a shoulder at 737 nm, tailing until ca. 800 nm. The HOMO level was estimated as −5.26 eV, derived from the first reversible electron oxidation wave at ca. 0.93 V vs. Ag/AgCl reference electrode. The space charge limited current hole mobility of a pristine film is ca. 2.90×10−4 cm2 V−1 s−1. The preliminary characterization of simple bulk heterojunction solar cells provides a power conversion efficiency (PCE) of ca. 4.0 % with VOC=0.77 V, JSC=10.0 mA cm−2, and FF=52 %, based on the as-cast active layer without a processing additive or solvent vapor annealing. Thermal annealing the active layer at a mild temperature of 50 °C increased the PCE to 4.39 % due mainly to the improvement of the FF.