Polymer-Fullerene Miscibility

Intercalation of fullerenes between side chains mostly determines the optimum polymer fullerene blending ratios. These findings offer explanations why large-scale phase separation occurs in some polymer fullerene blend ratios while thermodynamically stable mixing on the molecular scale occurs for others. High fullerene content is necessary to create the phase separation needed for efficient BHJ solar cells, which leads to optimum blend ratios near 1 3 to 1 4 polymenfullerene if intercalation occurs. If no intercalation occurs, an optimum near 1 1 is usually found. 

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Heterogeneous mixing of fullerenes and fullerene derivatives with Ji-conjugated polymers has been used to produce excellent materials for photovoltaic devices [141], Upon irradiation of fullerene/polymer blends, charge transfer from the polymer to occurs, resulting in efficient photoconductivities. Better behavior of fullerene derivatives than with pristine Cgg has been observed, and attributed to the improved miscibility of the functionalized species. 

The miscibility of different Cgo-containing polystyrenes with other polymers was studied in attempts to transfer the fullerene properties to the resulting polymer blends [71]. It was found that poly(2,6-dimethyl-l,4-phenylene oxide), PPO, is miscible with all the PS/Cgo samples investigated, whereas in the case of poly (vinyl methyl ether), PVME, PS/Cgo samples were miscible only for lower contents of Cgo [71]. 

Goh HW, Goh SH, Xu GQ (2002) Synthesis and miscibility studies of [60] fullerenated poly (2-hydroxyethyl methacrylate). J Polym Sci Part A Polym Chem 40 1157-1166... 

The choice of casting solvents became a clear issue in 2001 when Shaheen et al. published an article showing a PCE increase firom 1.1 to 2.5 % for MDMO-PPV PCBM OPV devices cast from toluene and chlorobenzene, respectively [36]. Subsequent studies showed that toluene was a better solvent for the MDMO-PPV than PCBM, so the PCBM crystallized out of solution with large domain sizes (>1 pm) that reduced the device quality [69]. However, chlorobenzene and dichlorobenzene are equally good solvents for both polymer and fullerene so the polymer and fullerene remain miscible to higher concentrations and the resulting domain sizes are much smaller (tens of nanometers) [69]. 

For adjusting interfacial interactions in fullerene-polymer composite materials, in addition to changing the miscibility of C-60, novel block copolymers have also been prepared, in which one of the blocks contains C-60 grafts. For example, Richard and co-workers synthesized novel rod-coil block copolymers of P3HT and PS-graft-fullerene, observing significant... 

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