title: Acceptor-donor-acceptor small molecules based on indacenodithiophene for efficient organic solar cells.
abstract: Four A-D-A type small molecules using 4,4,9,9-tetrakis(4-hexylphenyl)- indaceno[1,2-b:5,6-b']dithiophene as central building block, bithiophene or terthiophene as π-bridges, alkyl cyanoacetate or rhodanine as end acceptor groups were synthesized and investigated as electron donors in solution-processed organic solar cells (OSCs). These molecules showed excellent thermal stability with decomposition temperatures over 360 °C, relatively low HOMO levels of -5.18 to -5.22 eV, and strong optical absorption from 350 to 670 nm with high molar extinction coefficient of 1.1 × 10(5) to 1.6 × 10(5) M(-1) cm(-1) in chloroform solution. OSCs based on blends of these molecules and PC71BM achieved average power conversion efficiencies of 2.32 to 5.09% (the best 5.32%) after thermal annealing. The effects of thiophene bridge length and end acceptor groups on absorption, energy level, charge transport, morphology, and photovoltaic properties of the molecules were investigated.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
authors.forename: Huitao
authors.initials: H
authors.lastname: Bai
authors.forename: Yifan
authors.initials: Y
authors.lastname: Wang
authors.forename: Pei
authors.initials: P
authors.lastname: Cheng
authors.forename: Yongfang
authors.initials: Y
authors.lastname: Li
authors.forename: Daoben
authors.initials: D
authors.lastname: Zhu
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Zhan