Journal
ADVANCED ENERGY MATERIALS
Volume 7, Issue 7, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/aenm.201602000
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Funding
- ONR [N00141512322]
- UNC-GA Research Opportunity Grant
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
- National Basic Research Program 973 [2014CB643501]
- NSFC [91333204, 21325419]
- Chinese Academy of Sciences [XDB12030200]
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Organic solar cells (OSCs) made of donor/acceptor bulk-heterojunction active layers have been of widespread interest in converting sunlight to electricity. Characterizing of the complex morphology at multiple length scales of polymer: nonfullerene small molecular acceptor (SMA) systems remains largely unexplored. Through detailed characterizations (hard/soft X-ray scattering) of the record-efficiency polymer: SMA system with a close analog, quantitative morphological parameters are related to the device performance parameters and fundamental morphology-performance relationships that explain why additive use and thermal annealing are needed for optimized performance are established. A linear correlation between the average purity variations at small length scale (approximate to 10 nm) and photovoltaic device characteristics across all processing protocols is observed in approximate to 12%-efficiency polymer: SMA systems. In addition, molecular interactions as reflected by the estimated Flory-Huggins interaction parameters are used to provide context of the room temperature morphology results. Comparison with results from annealed devices suggests that the two SMA systems compared show upper and lower critical solution temperature behavior, respectively. The in-depth understanding of the complex multilength scale nonfullerene OSC morphology may guide the device optimization and new materials development and indicates that thermodynamic properties of materials systems should be studied in more detail to aid in designing optimized protocols efficiently.
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