Journal
ADVANCED ENERGY MATERIALS
Volume 9, Issue 16, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/aenm.201804021
Keywords
acceptors; nonfullerene; organic photovoltaic cells; organic solar cells; rhodanine
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Funding
- Korea Institute of Energy Technology Evaluation AMP
- Planning (KETEP)
- Ministry of Trade, Industry Energy [20173010012960]
- National Research Foundation of Korea (NRF) - Ministry of Science AMP
- ICT of the Republic of Korea [NRF-2015R1A1A3A04001498, NRF-2019R1A2C1003679]
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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 p-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.
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