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Issue 12, 2020
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Efficient light-harvesting, energy migration, and charge transfer by nanographene-based nonfullerene small-molecule acceptors exhibiting unusually long excited-state lifetime in the film state

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Abstract

Electron-acceptor small-molecules possessing a long exciton lifetime and a narrow energy band gap, opposing the energy gap law, are highly desirable for high-performance organic photovoltaics (OPVs) by realizing their efficient light-harvesting ability (LH), exciton diffusion (ED), and charge transfer (CT). Toward this goal, we designed an acceptor–donor–acceptor (A–D–A) type nonfullerene acceptor (NFA), TACIC, having an electron-donating, self-assembling two-dimensional (2D) nanographene unit, thienoazacoronene, at the center with electron-withdrawing groups at both ends. The TACIC film exhibited a narrow band gap (1.59 eV) with excellent LH. Surprisingly, the TACIC film showed an extremely long exciton lifetime (1.59 ns), suppressing undesirable nonradiative decay by its unique self-assembling behavior. When combined with a conjugated polymer donor, PBDB-T, slow ED and CT were observed (60 ps) with the excitation of TACIC owing to the large TACIC domain sizes. Nevertheless, the unusually high efficiencies of ED and CT (96% in total) were achieved by the long TACIC exciton lifetime. Additionally, unusual energy transfer (EnT) from the excited PBDB-T to TACIC was seen, demonstrating its dual LH role. The OPV device with PBDB-T and TACIC showed a high incident photon-to-current efficiency (IPCE) exceeding 70% at up to 710 nm and a power conversion efficiency of ∼10%. This result will open up avenues for a rational strategy of OPVs where LH, ED, and CT from the acceptor side as well as LH, EnT, ED, and CT from the donor side can be better designed by using 2D nanographene as a promising building block for high-performance A–D–A type NFAs.

Graphical abstract: Efficient light-harvesting, energy migration, and charge transfer by nanographene-based nonfullerene small-molecule acceptors exhibiting unusually long excited-state lifetime in the film state

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Supplementary files

Article information


Submitted
20 Dec 2019
Accepted
11 Feb 2020
First published
05 Mar 2020

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2020,11, 3250-3257
Article type
Edge Article

Efficient light-harvesting, energy migration, and charge transfer by nanographene-based nonfullerene small-molecule acceptors exhibiting unusually long excited-state lifetime in the film state

T. Umeyama, K. Igarashi, D. Sasada, Y. Tamai, K. Ishida, T. Koganezawa, S. Ohtani, K. Tanaka, H. Ohkita and H. Imahori, Chem. Sci., 2020, 11, 3250
DOI: 10.1039/C9SC06456G

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