Impact of acceptor crystallinity on the photophysics of nonfullerene blends for organic solar cells

Shaw, Paul E., Wolfer, Pascal, Langley, Benjamin, Burn, Paul L. and Meredith, Paul (2014) Impact of acceptor crystallinity on the photophysics of nonfullerene blends for organic solar cells. Journal of Physical Chemistry C, 118 25: 13460-13466. doi:10.1021/jp503150u

Author Shaw, Paul E.
Wolfer, Pascal
Langley, Benjamin
Burn, Paul L.
Meredith, Paul
Title Impact of acceptor crystallinity on the photophysics of nonfullerene blends for organic solar cells
Journal name Journal of Physical Chemistry C   Check publisher's open access policy
ISSN 1932-7447
Publication date 2014-01-01
Year available 2014
Sub-type Article (original research)
DOI 10.1021/jp503150u
Volume 118
Issue 25
Start page 13460
End page 13466
Total pages 7
Place of publication Washington DC United States
Publisher American Chemical Society
Language eng
Formatted abstract
To date, nonfullerene acceptors for organic solar cells have yet to reach the overall device performance achieved with fullerene derivatives. Power conversion efficiencies are low, even when combined with narrow optical gap polymers, with the processing conditions and blend microstructure difficult to optimize. To understand the potential origins of the decreased performance, we performed a photophysical study on a model system of blends of poly(3-n-hexylthiophene) (P3HT) with the planar small molecule electron acceptor 2-[{7-(9,9-di-n-propyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazol-4-yl}methylene]malononitrile (K12), focusing, in particular, on the effects of the crystallinity of the K12 phase on exciton dissociation and charge generation. Our results show that the microstructure of the blends can be manipulated by the processing conditions to give amorphous through to (semi)crystalline films. The amorphous blends show strong quenching of the photoluminescence, which indicates that there is a fine mixture of P3HT and K12. After annealing, the blends all showed increased photoluminescence and signs of phase separation with the formation of large-scale crystalline K12 domains. Photoinduced absorption spectroscopy confirmed the presence of positive polarons in the P3HT and revealed triplet excitons in blends containing crystalline K12 domains, indicating that exciton harvesting from the K12 phase was inefficient. However, charge generation in the 1:2 blend (the best for devices) was enhanced in the (semi)crystalline films, which suggests that aggregation of the P3HT and K12 aids charge separation. Hence, the complex phase behavior of K12 results in a trade-off between charge generation and collection against exciton harvesting from the K12 phase.
Keyword Free-carrier generation
Conjugated polymers
Q-Index Code C1
Q-Index Status Confirmed Code
Grant ID DE120101721
PA00P2 145395
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mathematics and Physics
Official 2015 Collection
School of Chemistry and Molecular Biosciences
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Citation counts: TR Web of Science Citation Count  Cited 7 times in Thomson Reuters Web of Science Article | Citations
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