Centre for Plastic Electronics and Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK.
Soft Matter. 2017 Jan 25;13(4):827-835. doi: 10.1039/c6sm01183g.
We report the impact of the ternary solution phase behaviour on the film morphology and crystallization of a model polymer:fullerene system. We employ UV-Vis absorption spectroscopy, combined with sequential filtration and dilution, to establish the phase diagram for regio-random poly(3-hexylthiophene-2,5-diyl) and phenyl-C61-butyric acid methyl ester (PCBM) in chlorobenzene. Films are systematically cast from one- and two-phase regions decoupling homogeneous and heterogenous nucleation, and the role of pre-formed aggregates from solutions. Increasing annealing temperature from 120 to 200 °C reveals a highly non-monotonic nucleation profile with a maximum at 170 °C, while the crystal growth rate increases monotonically. UV ozonolysis is employed to vary substrate energy, and found to increase nucleation rate and to promote a binary crystallization process. As previously found, exposure to light, under an inert atmosphere, effectively suppresses homogeneous nucleation; however, it has a considerably smaller effect on heterogeneous nucleation, either from solution aggregates or substrate-driven. Our results establish a quantitative link between solution thermodynamics, crystallization and provide insight into morphological design based on processing parameters in a proxy organic photovoltaic system.
富勒烯体系的薄膜形态和结晶的影响。我们采用紫外-可见吸收光谱，结合顺序过滤和稀释，建立了在氯苯中无规共聚 3-己基噻吩-2,5-二基和苯基-C61-丁酸甲酯（PCBM）的相图。从单相区和两相区系统地浇铸薄膜，从而解耦均相和异相成核，以及从溶液中预先形成的聚集体的作用。将退火温度从 120°C 增加到 200°C 揭示了一个高度非单调的成核曲线，在 170°C 处达到最大值，而晶体生长速率则单调增加。采用紫外臭氧氧化来改变衬底能量，发现其可以提高成核速率，并促进二元结晶过程。如前所述，在惰性气氛下暴露于光下会有效地抑制均相成核；然而，它对异相成核的影响要小得多，无论是来自溶液聚集体还是衬底驱动的成核。我们的结果在一个模拟有机光伏系统中建立了溶液热力学、结晶之间的定量联系，并为基于处理参数的形态设计提供了深入了解。
