Acceptor manipulation of bisalkylthiothienyl benzo[1,2-b:4,5-b']dithiophene core-structured oligomers for efficient organic photovoltaics

Three novel small molecules named DR3TDST, DRCN3TDST and DB3TDST containing bisalkylthiothienyl side-chain on benzo[1,2-b:4,5-b']dithiophene (BDT) core with different electron-deficient ending-groups are designed and synthesized. All three molecules have deep HOMO energy level from −5.40 eV to −5.44 eV, indicating introduction of bisalkylthio group to BDT is an effective method to modulate the molecular energy levels. Different ending-groups exhibit small but measurable effects on absorption, energy level, charge transport, morphology, and photovoltaic properties of small molecules. Bulk heterojunction solar cells fabricated with DRCN3TDST and PC₇₁BM deliverer the highest power conversion efficiency (PCE) of 5.17% after annealing and solvent vapor annealing.