標題: Surface and interface porosity of polymer/fullerene-derivative thin films revealed by contrast variation of neutron and X-ray reflectivity
作者: Liu, Heng-Jui
Jeng, U-Ser
Yamada, Norifumi L.
Su, An-Chung
Wu, Wei-Ru
Su, Chun-Jen
Lin, Su-Jien
Wei, Kung-Hwa
Chiu, Mao-Yuan
材料科學與工程學系
Department of Materials Science and Engineering
公開日期: 2011
摘要: Contrast variation of neutron and X-ray reflections has been adapted to reveal the film in-depth (vertical) composition profiles of the blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) for bulk heterojunction thin-film solar cells, with a PCBM/P3HT weight ratio of c = 0.6, 0.8 and 1.0. The X-ray scattering-length-density (SLD) profiles, extracted from X-ray reflectivity for the blend films spun-cast on Si wafer, exhibit a stratified film morphology of ca. 85 nm film thickness; the corresponding neutron SLD profiles extracted for the same films further elucidate a PCBM-enriched interfacial layer adjacent to the Si substrate. In contrast to the often assumed two-phase model, a three-phase model with porosity included as the third phase has to be used in deducing the absolute volume fractions of PCBM and P3HT from the complementary neutron and X-ray SLD profiles. In general, the thus deduced in-depth composition profiles for the blend films comprise a substantial surface layer (10-15 nm) of ca. 40% porosity, a 50 nm main layer with relatively uniform PCBM-P3HT composition, and a PCBM-enriched interface layer (similar to 20 nm) with similar to 15% porosity. Formation of the surface porosity is related to interfacial instability occurred in a transient surface layer upon film drying. Annealing at 150 degrees C influences modestly the vertical phase separation of the film, but drastically activates local phase separation for formation and growth of PCBM and P3HT nanodomains, as revealed by grazing incidence small/wide angle X-ray scattering. The surface/interface porosity features (overlooked in nearly all the previous studies) and the composition-dependent vertical phase separation bear hints in advancing device performance via interfacial morphology optimization.
URI: http://hdl.handle.net/11536/25913
http://dx.doi.org/10.1039/c1sm06005h
ISSN: 1744-683X
DOI: 10.1039/c1sm06005h
期刊: SOFT MATTER
Volume: 7
Issue: 19
起始頁: 9276
結束頁: 9282
顯示於類別:期刊論文


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  1. 000295085700072.pdf