To explore the efficient way of assembling electron-donating (D) and -accepting (A) moieties in small-molecule donors for organic solar cells (OSCs), ADA- and DAD-type triad donor molecules were synthesized and investigated using indolo-[3,2-b]indole and diketopyrrolopyrrole (DPP) as D and A moieties, respectively. Designing D−A-type donor materials possessing intramolecular charge-transfer (ICT) characteristics is important to facilitate exciton dissociation and retard charge-carrier recombination at the donor and acceptor (PC61BM) interface of bulk heterojunction OSCs. While ADA and DAD triad donors showed similar absorption spectra, their photoinduced ICT nature in the excited state monitored by the transient absorption spectroscopy was quite different. Both molecules exhibit strong electronegativity and abundance of electrons on DPP moieties, facilitating interaction with the neighboring molecules. However, ADA exhibits stronger ICT character than DAD because of the spatially more delocalized lowest unoccupied molecular orbital and abundant electron density at the end-capping DPP moieties. Owing to its stronger ICT character in the excited state, the ADA:PC61BM blend showed more favorable charge separation and reduced charge-carrier recombination at the donor/PC61BM interface. Consequently, ADA:PC61BM devices exhibited higher JSC than DAD:PC61BM OSCs.
Bibliographical noteFunding Information:
The work carried out at Seoul National University was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (2017R1E1A1A01075372[RIAM0417-20200051]), and the Korea Institute of Energy Technology Evaluation and Planning (KETEP) from the Ministry of Trade, Industry & Energy, Republic of Korea (no. 0417-20200029). The work carried out at Yonsei University was supported by the National Research Foundation of Korea grant funded by Korea government (NRF-2016R1E1A1A01943379).
© 2020 American Chemical Society
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films