Realizing over 10% efficiency in polymer solar cell by device optimization

The low band gap polymer based on benzodithiophene (BDT)-thieno[3,4-b]thiophene (TT) backbone, PBDT-TS1, was synthesized following our previous work and the bulk heterojunction (BHJ) material comprising PBDT-TS1/PC71BM was optimized and characterized. By processing the active layer with different additives i.e. 1,8-diiodooctane (DIO), 1-chloronaphthalene (CN) and 1, 8-octanedithiol (ODT) and optimizing the ratio of each additive in the host solvent, a high PCE of 9.98% was obtained under the condition of utilizing 3% DIO as processing additive in CB. The effect of varied additives on photovoltaic performance was illustrated with atomic force microscopy (AFM) and transmission electron microscope (TEM) measurements that explained changes in photovoltaic parameters. These results provide valuable information of solvent additive choice in device optimization of PBDTTT polymers, and the systematic device optimization could be applied in other efficient photovoltaic polymers. Apparently, this work presents a great advance in single junction PSCs, especially in PSCs with conventional architecture.