The Miscibility and Depth Profile of PCBM in P3HT: Thermodynamic Information to Improve Organic Photovoltaics
- ORNL
Recent work has shown that poly(3-hexylthiophene) (P3HT) and the surface functionalized fullerene 1-(3-methyloxycarbonyl)propy(1-phenyl [6,6]) C61 (PCBM) are much more miscible than originally thought, and the evidence of this miscibility requires a return to understanding the optimal morphology and structure of organic photovoltaic active layers. This manuscript describes the results of experiments that were designed to provide quantitative thermodynamic information on the miscibility, interdiffusion, and depth profile of P3HT:PCBM thin films that are formed by thermally annealing initial bilayers. It is found that the resultant thin films consist of a bulk layer that is not influenced by the air or substrate surface. The composition of PCBM in this bulk layer increases with increased PCBM loading in the original bilayer until the bulk layer contains 22 vol% PCBM. The introduction of additional PCBM into the sample does not increase the amount of PCBM dispersed in this bulk layer. This observation is interpreted to indicate that the miscibility limit of PCBM in P3HT is 22 vol%, while the precise characterization of the depth profiles in these films shows that the PCBM selectively segregates to the silicon and near air surface. The selective segregation of the PCBM near the air surface is ascribed to an entropic driving force.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 1038822
- Journal Information:
- Physical Chemistry Chemical Physics, Vol. 14, Issue 16; ISSN 1463-9076
- Country of Publication:
- United States
- Language:
- English
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