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Simple Bithiophene–Rhodanine‐Based Small Molecule Acceptor for Use in Additive‐Free Nonfullerene OPVs with Low Energy Loss of 0.51 eV

The introduction of rigid and extended ladder‐type fused‐ring cores, such as indacenodithiophene, has enabled the synthesis of a variety of nonfullerene small molecules for use as electron acceptors in high‐performance organic photovoltaic cells. Contrasting with recent trends, a very simple‐structu...

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Bibliographic Details
Published in:Advanced energy materials 2019-04, Vol.9 (16), p.n/a
Main Authors: Lee, Taeho, Eom, Yoonho, Song, Chang Eun, Jung, In Hwan, Kim, Dongwook, Lee, Sang Kyu, Shin, Won Suk, Lim, Eunhee
Format: Article
Language:English
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Summary:The introduction of rigid and extended ladder‐type fused‐ring cores, such as indacenodithiophene, has enabled the synthesis of a variety of nonfullerene small molecules for use as electron acceptors in high‐performance organic photovoltaic cells. Contrasting with recent trends, a very simple‐structured nonfullerene acceptor (NFA), T2‐ORH, consisting of a bithiophene core and octyl‐substituted rhodanine ends, is synthesized in two steps from inexpensive commercially available raw materials. Its relatively short π‐conjugation results in a wide bandgap and a blue‐shifted UV–vis absorption profile complementary to those of poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐co‐3‐fluorothieno[3,4‐b]thiophene‐2‐carboxylate] (PTB7‐Th). Despite a sufficient offset between T2‐ORH and PTB7‐Th, the lowest unoccupied molecular orbital (LUMO) energy level of T2‐ORH is still higher than the LUMOs of other NFAs (e.g., ITIC). Therefore, the PTB7‐Th:T2‐ORH blend film exhibits an efficiency of 9.33% with a high open‐circuit voltage of 1.07 V and a short‐circuit current of 14.72 mA cm−2 in an additive‐free single‐junction cell. Importantly, the optimized device displays a remarkably low energy loss of 0.51 eV, in which bimolecular and monomolecular charge recombination is effectively suppressed by solvent vapor annealing treatment. The blend film has a very smooth and homogeneous morphology, providing both vertical and parallel charge transport in the devices. A very simple rod‐shaped bithiophene‐based small molecule, T2‐ORH, is synthesized in only two steps to obtain a nonfullerene acceptor for use in efficient organic photovoltaic cells. The additive‐free inverted PTB7‐Th:T2‐ORH single‐junction device exhibits a power conversion efficiency of 9.33%, with a remarkably low Eloss of 0.51 eV due to a smooth homogeneous film morphology and vertical and parallel charge transport.
ISSN:1614-6832
1614-6840
DOI:10.1002/aenm.201804021