  An oligomeric semiconductor containing three bisthiophenediketopyrrolopyrole
units (Tri-BTDPP) was synthesized and characterized. Tri-BTDPP has a HOMO level
of -5.34 eV, a broad absorption close to the near infrared region and a low
band gap of 1.33 eV. Additionally, a promising hole mobility of 1 x 10-3 cm V-1
s-1 was achieved after thermal annealing at 150 C in organic field effect
transistors (OFET). Organic photovoltaic (OPV) cells containing Tri-BTDPP and
PC71BM as the donor/acceptor couple exhibited a power conversion efficiency
(PCE) of 0.72%. Through an intensive study of the active layer using AFM, XRD,
and DSC, it was found that Tri-BTDPP and PC71BM were unable to intermix
effectively, resulting in oversized Tri-BTDPP crystalline phases and thus poor
charge separation. Strategies to improve the OPV performance were thus
proposed.
