The relative dielectric constant εr of PTB7:PCBM is given as 3.5 in the paper at the link:https://www.researchgate.net/profile/Kibeom_Kim3/publication/262605189_Electron_Collection_as_a_Limit_to_PolymerPCBM_Solar_Cell_Efficiency_Effect_of_Blend_Microstructure_on_Carrier_Mobility_and_Device_Performance_in_PTB7PCBM/links/5445caac0cf22b3c14ddeedd.pdf. In the paper you will fined also information about the mobility.
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Article Electron Collection as a Limit to Polymer:PCBM Solar Cell Ef...
The relative dielectric constant εr of PTB7:PCBM is given as 3.5 in the paper at the link:https://www.researchgate.net/profile/Kibeom_Kim3/publication/262605189_Electron_Collection_as_a_Limit_to_PolymerPCBM_Solar_Cell_Efficiency_Effect_of_Blend_Microstructure_on_Carrier_Mobility_and_Device_Performance_in_PTB7PCBM/links/5445caac0cf22b3c14ddeedd.pdf. In the paper you will fined also information about the mobility.
Best wishes
Article Electron Collection as a Limit to Polymer:PCBM Solar Cell Ef...