The phase behavior of a polymer-fullerene bulk heterojunction system that contains bimolecular crystals
✍ Scribed by Nichole Cates Miller; Roman Gysel; Chad E. Miller; Eric Verploegen; Zach Beiley; Martin Heeney; Iain McCulloch; Zhenan Bao; Michael F. Toney; Michael D. McGehee
- Book ID
- 105339537
- Publisher
- John Wiley and Sons
- Year
- 2011
- Tongue
- English
- Weight
- 710 KB
- Volume
- 49
- Category
- Article
- ISSN
- 0887-6266
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✦ Synopsis
Abstract
Polymer:fullerene blends have been widely studied as an inexpensive alternative to traditional silicon solar cells. Some polymer:fullerene blends, such as blends of poly(2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene (pBTTT) with phenyl‐c71‐butyric acid methyl ester (PC~71~BM), form bimolecular crystals due to fullerene intercalation between the polymer side chains. Here we present the determination of the eutectic pBTTT:PC~71~BM phase diagram using differential scanning calorimetry (DSC) and two‐dimensional grazing incidence X‐ray scattering (2D GIXS) with in‐situ thermal annealing. The phase diagram explains why the most efficient pBTTT:PC~71~BM solar cells have 75–80 wt % PC~71~BM since these blends lie in the center of the only room‐temperature phase region containing both electron‐conducting (PC~71~BM) and hole‐conducting (bimolecular crystal) phases. We show that intercalation can be suppressed in 50:50 pBTTT:PC~71~BM blends by using rapid thermal annealing to heat the blends above the eutectic temperature, which forces PC~71~BM out of the bimolecular crystal, followed by quick cooling to kinetically trap the pure PC~71~BM phase. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011