Ternary Blend Bulk-Heterojunction Solar Cells Based on Active Layers of PTB7, PC71BM, and PC61BM

Bulk-heterojunction solar cells were fabricated using ternary blend dichlorobenzene solutions of poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7):[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) with different weight ratios between PC61BM and PC71BM. In all the solar cells, the overall weight ratio of polymer to fullerene was maintained at 1:1.5, while the composition of the fullerene component (PC61BM:PC71BM) was varied. The measurement results of the solar cell performance showed that the open-circuit voltage notably increased for PC61BM weight fractions between 10% and 90%, while it decreased at 100%. The short-circuit current showed the most significant increase in the PC61BM weight fraction range between 50% and 60%. A power conversion efficiency of 3.4% was achieved when the PC61BM weight fraction was between 50% and 60%. These results may suggest that the transport of the photoexcited electrons between the cathode and the PC61BM/PC71BM nanodomains was enhanced.