[Understanding the Effected Efficiencies of Polymer Solar Cells Employing Different Fullerene Multiadducts as Acceptors].

The application of fullerenes with two or more adducts as acceptors has greatly enhanced the performance of bulk-heterojunction solar cells with poly (3-hexylthiophene) (P3HT) as the donor. The enhancement is caused by a substantial increase in the open-circuit voltage due to a rise in the fullerene lowest unoccupied molecular orbital (LUMO) level when going from monoadducts to multiadducts. While the increase in the open-circuit voltage is obtained with many different polymers, most polymers other than P3HT show a substantially reduced photocurrent when blended with fullerene multi-adducts such as bis adduct of Phenyl-C61 -butyric acid methyl ester (bis-PCBM) or the indene-C60 bis-adduct (ICBA). Here we investigate the reasons for this change in performance of polymer solar cells(PSCs) based on [6,6]-phenyl C70-butyric acid methyl ester (PC70BM), ICBA and bis-PC70BM as the acceptors and 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)as the donor. The cell configuration is ITO/PEDOT：PSS/active layer /LiF/Al .The PSCs with PC70BM, ICBA and bis-PC70BM show PCEs of 7.29%, 4.92% and 3.33%, respectively. The change of performance of the PSCs could be mainly attributed to the different excition generation and charge collection of PSCs employing different fullerene multi-adducts as acceptors.