Visualizing nanoscale phase morphology for understanding photovoltaic performance of PTB7: PC71BM solar cell

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Author list: Supasai T., Amornkitbamrung V., Thanachayanont C., Tang I.-M., Sutthibutpong T., Rujisamphan N.

Publisher: Elsevier

Publication year: 2017

Journal: Applied Surface Science (0169-4332)

Volume number: 422

Start page: 509

End page: 517

Number of pages: 9

ISSN: 0169-4332

eISSN: 1873-5584

URL: https://www.scopus.com/inward/record.uri?eid=2-s2.0-85020404605&doi=10.1016%2fj.apsusc.2017.05.205&partnerID=40&md5=1730db57b94b8d44460697d0ffa7f031

Languages: English-Great Britain (EN-GB)

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Abstract

Visualizing and controlling the phase separation of the donor and acceptor domains in organic bulk-hetero-junction (BHJ) solar devices made with poly([4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethyl-hexyl)carbon-yl]thieno[3,4-bthiophenediyl]) (PTB7) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) are needed to achieve high power conversion efficiency (PCE). Traditional bright-field (BF) imaging, especially of polymeric materials, produces images of poor contrast when done at the nanoscale level. Clear nanoscale morphologies of the PTB7:PC71BM blends prepared with different 1,8-diiodooctane (DIO) concentrations were seen when using the energy-filtered transmission electron microscopy (EFTEM). The electron energy loss (EELS) spectra of the pure PTB7 and PC71BM samples are centered at 22.7 eV and 24.5 eV, respectively. Using the electrons whose energy losses are in the range of 16–30 eV, detail information of the phase morphology at the nanoscale was obtained. Correlations between the improvement in the photovoltaic performances and the increased electron mobility were seen. These correlations are discussed in terms of the changes (at the nanoscale level) in blending phase morphology when different DIO concentrations are added. © 2017 Elsevier B.V.

Keywords

Electron energy loss, Energy-filtered TEM, Nano-scale blend, PTB7:PC71BM