title: Photocurrent enhancement in diketopyrrolopyrrole solar cells by manipulating dipolar anchoring terminals on alkyl-chain spacers.
abstract: We chose DPP-BDT-DPP {DPP=diketopyrrolopyrrole, BDT=4,8-di-[2-(2-ethylhexyl)-thienyl]benzo[1,2-b:4,5-b']dithiophene} as a model backbone and varied the anchoring groups [C5 H11 , COOCH3 , and SiCH3 (OSiCH3 )2 ] terminated on the N-substituted alkyl-chain spacer of the DPP units to study the effect of anchoring terminals on the morphology of blend film and on the device performances of bulk heterojunction solar cells. By replacing the nonpolar C5 H11 anchoring terminal with the polar COOCH3 anchoring terminal leads to an enhancement in the short-circuit current density (Jsc ) (4.62 vs. 9.32 mA cm(-2) ), whereas the value of Jsc sharply decreases to 0.45 mA cm(-2) if the C5 H11 anchoring terminal is replaced by a SiCH3 (OSiCH3 )2 group. The changes in Jsc are associated with changes in the π-π stacking distance (3.39→3.34 Å vs. 3.39→3.45 Å) and the phase size (50→20 nm vs. 50→>250 nm) through alteration of the anchoring group from C5 H11 to COOCH3 versus from C5 H11 to SiCH3 (OSiCH3 )2 . Interestingly, the anchoring terminals bring about drastic changes in molecular orientations, which result in different out-of-plane hole transport. This is the first time this effect has been systemically demonstrated to improve photocurrent generation by manipulating the dipolar anchoring groups terminated on the alkyl-chain spacer.
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; Graduate School, Chinese Academy of Sciences, Beijing, 100190 (P. R. China).
authors.forename: Ailing
authors.initials: A
authors.lastname: Tang
authors.forename: Zhenhuan
authors.initials: Z
authors.lastname: Lu
authors.forename: Shuming
authors.initials: S
authors.lastname: Bai
authors.forename: Jianhua
authors.initials: J
authors.lastname: Huang
authors.forename: Yuxia
authors.initials: Y
authors.lastname: Chen
authors.forename: Qiang
authors.initials: Q
authors.lastname: Shi
authors.forename: Chuanlang
authors.initials: C
authors.lastname: Zhan
authors.forename: Jiannian
authors.initials: J
authors.lastname: Yao
keywords: anchoring terminals; film morphology; molecular orientation; photocurrent; thin films