Narrow band gap conjugated polymer for improving the photovoltaic performance of P3HT:PCBM ternary blend bulk heterojunction solar cells

A new D–A structured conjugated polymer (PBDO-T-TDP) based on electron-rich benzo[1,2-b:4,5-b′] difuran (BDO) containing conjugated alkylthiophene side chains with an electron-deficient diketo-pyrrolopyrrole (DPP) derivative is designed and synthesized. The polymer shows a narrow band gap with broad UV-Visible absorption spectra, which is in contrast to that of the P3HT:PCBM binary blend. Furthermore, its energy levels can meet the energetic requirement of the cascaded energy levels of P3HT and PCBM. Therefore, PBDO-T-TDP is used as a sensitizer in P3HT:PCBM based BHJ solar cells and its effect on their photovoltaic properties was investigated by blending them together at various weight ratios. It is observed that the resulting ternary blend system exhibited a significant improvement in the device performance (∼3.10%) as compared with their binary ones (∼2.15%). Such an enhancement in the ternary blend system is ascribed to their balanced hole and electron mobility along with uniform distribution of PBDO-T-TDP in the blend system, as revealed by organic field effect transistors and AFM studies.