Novel solution processable small molecule containing new electron-withdrawing group and oligothiophene for photovoltaic applications

A novel electron-withdrawing group 5-(2,6-dimethyl-4H-pyran-4-ylidene)-1,3-diethyl-2-thioxo-dihydropyrimidine-4,6(1H,5H)-dione (PD) was designed and synthesized according to Knoevenagel condensation. On this basis, a small molecule 8TPDC8 with oligothiophene as electron-donating unit and PD as electron-accepting unit was designed and synthesized. UV–vis absorption spectrum displayed that 8TPDC8 possesses a relatively broad absorption range (from 300 to 900 nm). The cyclic voltammetry investigation displayed that the highest occupied molecular orbital (HOMO) energy level of 8TPDC8 was −5.28 eV, which promised good air stability and high open circuit voltage (Voc) for photovoltaic application. The bulk heterojunction (BHJ) photovoltaic devices were fabricated with 8TPDC8 as the donor material and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor material. A power conversion efficiency of 1.28% has been obtained under the illumination of AM 1.5, 100 mW/cm2.