In Situ Characterization of Polymer鈥揊ullerene Bilayer Stability

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• 作者：Deborah Leman ; Mary Allison Kelly ; Stuart Ness ; Sebastian Engmann ; Andrew Herzing ; Chad Snyder ; Hyun Wook Ro ; R. Joseph Kline ; Dean M. DeLongchamp ; Lee J. Richter
• 刊名：Macromolecules
• 出版年：2015
• 出版时间：January 27, 2015
• 年：2015
• 卷：48
• 期：2
• 页码：383-392
• 全文大小：485K
• ISSN：1520-5835

文摘

A consensus is emerging that mixed phases are present in bulk heterojunction organic photovoltaic (OPV) devices. Significant insights into the mixed phases have come from bilayer stability measurements, in which an initial sample consisting of material pure layers of donor and acceptor is thermally treated, resulting in swelling of one layer by the other. We present a comparative study of the stability of polymer/fullerene bilayers using two common OPV polymer donors poly(3-hexylthiophene), P3HT, and poly[N-9鈥?heptadecanyl-2,7-carbazole-alt-5,5-(4鈥?7鈥?di-2-thienyl-2鈥?1鈥?3鈥?benzothiadiazole)], PCDTBT, and four fullerene acceptors phenyl-C61-butyric acid methyl ester, phenyl-C71-butyric acid methyl ester, [60]PCBM bis-adduct, and indene C60 bis-adduct. Using in situ spectroscopic ellipsometry to characterize the quasi-steady state behavior of the films, we find that the polymer glass transition temperature (T_g) is critical to the bilayer stability, with no significant changes occurring below T_g of the high T_g PCDTBT. Above the polymer T_g, we find the behavior is irreversible and most consistent with swelling of the polymer by the fullerene, constrained by tie chains in the polymer network and influenced by the rubbery dynamics of the mixed region. The swelling varies significantly with the nature of the fullerene and the polymer. Across the eight systems studied, there is no clear relationship between swelling and OPV device performance. The relationship between the observed swelling and the underlying fullerene鈥損olymer miscibility is explored via Flory鈥揜ehner theory.