title: Phenyl-1,3,5-trithienyl-diketopyrrolopyrrole: a molecular backbone potentially affording high efficiency for solution-processed small-molecule organic solar cells through judicious molecular design.
abstract: Finding new molecular backbones is necessary for further advances in solution-processed small-molecule organic solar cells (SM-OSCs). Increasing molecular π conjugation generally enhances the light-harvesting ability, and the resulting strong π-π-stacking interactions improve the charge-carrier transport ability; both increase the efficiency. In this study, we focus on the phenyl-1,3,5-trithienyl (3T-P) backbone because of its C3 symmetry, planarity, and particularly high conjugation between the three arms through the core phenyl unit. When the three arms were functionalized with diketopyrrolopyrrole (DPP) units to afford 3D-T-P, only modest efficiency was achieved (1.16%). Introduction of 4,8-bis(2-(2-ethylhexylthienyl)) benzodithiophene (BDT) between the 3T-P and DPP units to give 3D-B-T-P enhanced the light-harvesting ability, and particularly improved the hole mobility by 1.5 orders of magnitude (5.91×10(-2) versus 1.05×10(-3) cm(2) V(-1) s(-1)). When using PC71BM as the acceptor material, 3D-B-T-P gave the best power conversion efficiency (PCE) of 2.27%, which is about 1.9 times higher than the best efficiency from 3D-T-P (≈1.16%). The efficiency can be improved up to 3.60% with 3% (v/v) of 1,8-diiodooctane (DIO) as the cosolvent and thermal annealing at 100 °C for 10 min. This PCE is, to the best of our knowledge, the highest efficiency reported to date among the phenyl-1,3,5-based C3-symmetric molecules. Removing one DPP unit from 3D-T-P to form 2D-T-P, or from 3D-B-T-P to form 2D-B-T-P both decreased the light-harvesting ability and the hole mobility, thereby affording lower efficiency. Taken together, our results demonstrate that the planar phenyl-1,3,5-trithienyl-based C3 -symmetric structure can be a promising backbone, and enhancing the conjugation of the 3D-T-P backbone can effectively improve the device performance.
authors.affiliation: Beijing National Laboratory of Molecular Science, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190 (P.R. China), Fax: (+86) 10-82616517; University of Chinese Academy of Sciences, Beijing 100039 (P.R. China).
authors.forename: Shanlin
authors.initials: S
authors.lastname: Zhang
authors.forename: Bo
authors.initials: B
authors.lastname: Jiang
authors.forename: Chuanlang
authors.initials: C
authors.lastname: Zhan
authors.forename: Jianhua
authors.initials: J
authors.lastname: Huang
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.forename: Hui
authors.initials: H
authors.lastname: Jia
authors.forename: Ailing
authors.initials: A
authors.lastname: Tang
authors.forename: Lili
authors.initials: L
authors.lastname: Chen
authors.forename: Jiannian
authors.initials: J
authors.lastname: Yao
keywords: donor-acceptor systems; heterocycles; molecular devices; small molecules; solar cells