Synthesis of organic semiconductor bearing B←N bridged thienylthiazole and diketopyrrolopyrrole for the applicaton of high open-circuit voltage organic photovoltaics

New small molecular semiconductors with small band gap and low-lying highest occupied molecular orbital (E-HOMO) namely TBDPPOT, TBDPPEH, and TBDPPEHT4 were synthesized by incorporating the B <- N bridged thienylthiazole and diketopyrrolopyrrole (DPP) derivatives. TBDPPOT and TBDPPEH were prepared, respectively, using two different DPPs having 1-octyl and 2-ethylhexyl moiety as the solubilizing group. In addition, the band gap of the TBDPPEH is further reduced by introducing planar thienothiophene unit, which was used for the preparation of TBDPPEHT4. These synthesized SMs are blended with fullerene derivative to construct a photo-active layer for organic photovoltaics. Among OPVs utilizing those SMs, the TBDPPEH exhibits highest power conversion efficiency of 3.21% with an exceptionally high V-OC of 0.92 V, which is ascribed to low-lying HOMO energy level of -5.62 eV. It is expected that the utilization of TBDPPEH as a photo-active layer for OPVs would enhance the oxidation stability of the OPVs.