Journal
SMALL METHODS
Volume 2, Issue 5, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/smtd.201700415
Keywords
fluorination; high domain purity; pentathiophene; small domain sizes
Funding
- National Basic Research Program of China (973 Program) [2013CB834701, 2014CB643501]
- ShenZhen Technology and Innovation Commission [JCYJ20170413173814007]
- Hong Kong Research Grants Council [T23-407/13 N, N_HKUST623/13, 16305915, 16322416, 606012, 16303917]
- Ministry of Science and Technology of China [2016YFA0200700]
- NSFC [21504066]
- Hong Kong Innovation and Technology Commission [ITC-CNERC14SC01, ITS/083/15]
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
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For oligothiophene-based donor polymers, changing the number of thiophene rings in each repeating unit is a simple and effective approach to tune their optical and electronic properties. While bithiophene-, terthiophene-, and quaterthiophene-based polymers have been widely known and studied, pentathiophene-based ones are rarely reported. Here, the pentathiophene-based polymer PT5T, which yields extremely poor device performance with an efficiency of only 0.37%, is synthesized. However, after the introduction of two fluorine atoms to the center thiophene unit, the resulting polymer (PT5T-2F) yields dramatic improvement in device performance with the fill factor and the power conversion efficiency improved to 70.8% and 9.69%, respectively. The morphological study shows that the difluorinated pentathiophene building block introduces enhanced molecular aggregation and crystallinity of PT5T-2F, which facilitates the formation of bulk heterojunction blends with higher domain purity. Most importantly, despite its high crystallinity, PT5T-2F can still produce reasonably small domain sizes in the polymer-based blend. The results indicate that the difluorinated pentathiophene is a promising building block to construct donor polymers for nonfullerene organic solar cells.
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