title: Butanedithiol Solvent Additive Extracting Fullerenes from Donor Phase To Improve Performance and Photostability in Polymer Solar Cells.
abstract: In this work, we demonstrated that the excited poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2,6-diyl)] (PTB7-Th) will be degraded by [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) or photolysis fragment of 1,8-diiodooctane (DIO) in the presence of oxygen and under irradiation of red light. From the previous reports, the fragment of DIO may be involved in the reaction directly. Our work indicates the PC71BM is not directly involved in the reaction, but is acting as a catalyst to promote the reaction of excited donors with oxygen. Thus, PTB7-Th urgently needs a kind of nonresidual iodine-free additive to replace DIO and remove the fullerene from the donor phase at the same time. Taking into consideration PC71BM solubility and boiling point difference between solvent additives and host solvents, 1,4-butanedithiol solvent was selected to fabricate PTB7-Th:PC71BM-based solar cells achieving a best power conversion efficiency (PCE) of 10.2% (8.5% for PTB7:PC71BM). Iodine-free butanedithiol can not only avoid excited polymer reacting with the photolysis fragment of DIO but also suppress the degradation of the excited PTB7-Th caused by synergistic effect between the fullerene and oxygen via extracting the free/trapped PC71BM from the donor phase. Eventually, the film prepared with 1,4-butanedithiol shows higher stability than the film prepared without any additives and much better than the film with DIO in macro-/micromorphology, light absorption, and device performance.
authors.affiliation: School of Material Science and Engineering and ‡College of Chemistry, Nanchang University , 999 Xuefu Avenue, Nanchang 330031, China.
authors.forename: Yuanpeng
authors.initials: Y
authors.lastname: Xie
authors.affiliation: School of Material Science and Engineering and ‡College of Chemistry, Nanchang University , 999 Xuefu Avenue, Nanchang 330031, China.
authors.forename: Xiaotian
authors.initials: X
authors.lastname: Hu
authors.affiliation: School of Material Science and Engineering and ‡College of Chemistry, Nanchang University , 999 Xuefu Avenue, Nanchang 330031, China.
authors.forename: Jingping
authors.initials: J
authors.lastname: Yin
authors.affiliation: School of Material Science and Engineering and ‡College of Chemistry, Nanchang University , 999 Xuefu Avenue, Nanchang 330031, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Zhang
authors.affiliation: School of Material Science and Engineering and ‡College of Chemistry, Nanchang University , 999 Xuefu Avenue, Nanchang 330031, China.
authors.forename: Xiangchuan
authors.initials: X
authors.lastname: Meng
authors.affiliation: School of Material Science and Engineering and ‡College of Chemistry, Nanchang University , 999 Xuefu Avenue, Nanchang 330031, China.
authors.forename: Guodong
authors.initials: G
authors.lastname: Xu
authors.affiliation: School of Material Science and Engineering and ‡College of Chemistry, Nanchang University , 999 Xuefu Avenue, Nanchang 330031, China.
authors.forename: Qingyun
authors.initials: Q
authors.lastname: Ai
authors.affiliation: School of Material Science and Engineering and ‡College of Chemistry, Nanchang University , 999 Xuefu Avenue, Nanchang 330031, China.
authors.forename: Weihua
authors.initials: W
authors.lastname: Zhou
authors.affiliation: School of Material Science and Engineering and ‡College of Chemistry, Nanchang University , 999 Xuefu Avenue, Nanchang 330031, China.
authors.forename: Yiwang
authors.identifier: http://orcid.org/0000-0003-4709-7623
authors.initials: Y
authors.lastname: Chen
keywords: butanedithiol; diiodooctane; excited polymer; photostability; solar cells; solvent additives