title: Effect of fullerene tris-adducts on the photovoltaic performance of P3HT:fullerene ternary blends.
abstract: Fullerene tris-adducts have the potential of achieving high open-circuit voltages (V(OC)) in bulk heterojunction (BHJ) polymer solar cells (PSCs), because their lowest unoccupied molecular orbital (LUMO) level is higher than those of fullerene mono- and bis-adducts. However, no successful examples of the use of fullerene tris-adducts as electron acceptors have been reported. Herein, we developed a ternary-blend approach for the use of fullerene tris-adducts to fully exploit the merit of their high LUMO level. The compound o-xylenyl C60 tris-adduct (OXCTA) was used as a ternary acceptor in the model system of poly(3-hexylthiophene) (P3HT) as the electron donor and the two soluble fullerene acceptors of OXCTA and fullerene monoadduct (o-xylenyl C60 monoadduct (OXCMA), phenyl C61-butyric acid methyl ester (PCBM), or indene-C60 monoadduct (ICMA)). To explore the effect of OXCTA in ternary-blend PSC devices, the photovoltaic behavior of the device was investigated in terms of the weight fraction of OXCTA (W(OXCTA)). When W(OXCTA) is small (<0.3), OXCTA can generate a synergistic bridging effect between P3HT and the fullerene monoadduct, leading to simultaneous enhancement in both V(OC) and short-circuit current (J(SC)). For example, the ternary PSC devices of P3HT:(OXCMA:OXCTA) with W(OXCTA) of 0.1 and 0.3 exhibited power-conversion efficiencies (PCEs) of 3.91% and 3.96%, respectively, which were significantly higher than the 3.61% provided by the P3HT:OXCMA device. Interestingly, for W(OXCTA) > 0.7, both V(OC) and PCE of the ternary-blend PSCs exhibited nonlinear compositional dependence on W(OXCTA). We noted that the nonlinear compositional trend of P3HT:(OXCMA:OXCTA) was significantly different from that of P3HT:(OXCMA:o-xylenyl C60 bis-adduct (OXCBA)) ternary-blend PSC devices. The fundamental reasons for the differences between the photovoltaic trends of the two different ternary-blend systems were investigated systemically by comparing their optical, electrical, and morphological properties.
authors.affiliation: Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea.
authors.forename: Hyunbum
authors.initials: H
authors.lastname: Kang
authors.forename: Ki-Hyun
authors.initials: KH
authors.lastname: Kim
authors.forename: Tae Eui
authors.initials: TE
authors.lastname: Kang
authors.forename: Chul-Hee
authors.initials: CH
authors.lastname: Cho
authors.forename: Sunhee
authors.initials: S
authors.lastname: Park
authors.forename: Sung Cheol
authors.initials: SC
authors.lastname: Yoon
authors.forename: Bumjoon J
authors.initials: BJ
authors.lastname: Kim
mesh_terms: D055664:Electrochemical Techniques / Q000379:methods*; D037741:Fullerenes / Q000737:chemistry*
chemical_list: D037741:Fullerenes