title: X-shaped oligothiophenes as a new class of electron donors for bulk-heterojunction solar cells.
abstract: Four X-shaped oligothiophenes with different conjugation length were investigated as novel electron donors in single-layer bulk-heterojunction solar cells. The UV-vis absorption spectra of blends of compounds 1-4 with 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C(61) show a remarkably red shift and broadening with increasing thiophene number at each of the four branches. The performance of the photovoltaic cells varied significantly with molecular structures of the four oligothiophenes. Conversion efficiencies increased from 0.008% to 0.8% with changing the electron donors from 1 to 4. The maximum incident photon-to-current conversion efficiency of the device based on 4 reaches 31.6%, much higher than those of three other compounds 1-3. Remarkable improvement of the device performance was achieved with increasing the substituted thiophene number. The results show that the photovoltaic effect is dependent on the structural characteristics and the film forming abilities of the X-shaped thiophenes.
authors.affiliation: Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, P. R. China.
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Sun
authors.forename: Yinhua
authors.initials: Y
authors.lastname: Zhou
authors.forename: Weicai
authors.initials: W
authors.lastname: Wu
authors.forename: Yunqi
authors.initials: Y
authors.lastname: Liu
authors.forename: Wenjing
authors.initials: W
authors.lastname: Tian
authors.forename: Gui
authors.initials: G
authors.lastname: Yu
authors.forename: Wenfeng
authors.initials: W
authors.lastname: Qiu
authors.forename: Shiyan
authors.initials: S
authors.lastname: Chen
authors.forename: Daoben
authors.initials: D
authors.lastname: Zhu