title: Efficient diketopyrrolopyrrole-based small-molecule bulk-heterojunction solar cells with different electron-donating end-groups.
abstract: A series of small molecules that contained identical π-spacers (ethyne), a central diketopyrrolopyrrole (DPP) unit, and different aromatic electron-donating end-groups were synthesized and used in organic solar cells (OSCs) to study the effect of electron-donating groups on the device performance. The three compounds, DPP-A-Ph, DPP-A-Na, and DPP-A-An, possessed intense absorption bands that covered a wide range, from 350 to 750 nm, and relatively low HOMO energy levels, from -5.50 to -5.55 eV. DPP-A-An, which contained anthracene end-groups, demonstrated a stronger absorbance and a higher hole mobility than DPP-A-Ph, which contained phenyl groups, and DPP-A-Na, which contained naphthalene units. The power-conversion efficiencies (PCEs) of OSCs based on organic:PC71BM blends (1:1, w/w) with a processed DIO additive were 3.93% for DPP-A-An, 3.02% for DPP-Na, and 2.26% for DPP-A-Ph. These findings suggest that a DPP core that is functionalized with electron-donating capping groups constitutes a promising new class of solution-processable small molecules for OSC applications.
authors.affiliation: POSTECH Organic Electronics Laboratory, Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 790-784 (Republic of Korea).
authors.forename: Yu Jin
authors.initials: YJ
authors.lastname: Kim
authors.forename: Jang Yeol
authors.initials: JY
authors.lastname: Back
authors.forename: Seul-Ong
authors.initials: SO
authors.lastname: Kim
authors.forename: Chan-Woo
authors.initials: CW
authors.lastname: Jeon
authors.forename: Chan Eon
authors.initials: CE
authors.lastname: Park
authors.forename: Yun-Hi
authors.initials: YH
authors.lastname: Kim
keywords: absorption; alkynes; conjugation; cross-coupling; solar cells