Two kinds of dumbbell-shaped acceptor-donor-acceptor (A-D-A)-type triad single-component (SC) photovoltaic molecules based on a benzodithiophene-rhodanine (BDTRh) core and [6,6]-phenyl-C61butyric acid (PC61BA) termini, BDTRh-C2-PC61BA and BDTRh-C10-PC61BA, were synthesized by modulating the alkyl (C2 and C10) spacer lengths. Both SC photovoltaic structures had similar UV-vis spectra in solution, but BDTRh-C10-PC61BA showed a significantly higher absorption coefficient as a thin film. In films, a more facile intermolecular photo-induced charge transfer was observed for BDTRh-C10-PC61BA in the broad-band transient absorption measurements. BDTRh-C10-PC61BA also exhibited a higher hole mobility (by 25 times) and less bimolecular recombination than BDTRh-C2-PC61BA. By plotting the normalized external quantum efficiency data, a higher charge-transfer state was measured for BDTRh-C10-PC61BA, reducing its voltage loss. A higher power conversion efficiency of ∼2% was obtained for BDTRh-C10-PC61BA, showing higher open-circuit voltage, short-circuit current density, and fill factor than those of BDTRh-C2-PC61BA devices. The different carrier dynamics, voltage loss, and optical and photoelectrical characteristics depending on the spacer length were interpreted in terms of the film morphology. The longer decyl spacer in BDTRh-C10-PC61BA afforded a significantly enhanced intermolecular ordering of the p-type core compared to BDTRh-C2-PC61BA, suggesting that the alkyl spacer length plays a critical role in controlling the intermolecular packing interaction.
Bibliographical noteFunding Information:
This work was financially supported by the National Research Foundation (NRF) of Korea (grants NRF-2019R1A2C2085290, 2019R1A6A1A11044070, 2020M3H4A3081814, and 2020R1A2C1014203) and the New Renewable Energy Core Technology Development Project of Korea Institute of Energy Technology Evaluation and Planning (KETEP) from the Ministry of Trade, Industry & Energy, Republic of Korea (20183010013900). We thank the Institute for Basic Science (IBS) Center for Molecular Spectroscopy and Dynamics (IBS-R023-D1) for providing (NMR Spectrometry) and professional technical support.
© 2021 American Chemical Society
- fullerene-based triads
- organic photovoltaics
- organic solar cells
- single-component organic solar cells
ASJC Scopus subject areas
- Materials Science(all)