Fluorinated and non-fluorinated conjugated polymers showing different photovoltaic properties in polymer solar cells with PFNBr interlayers

Photovoltaic properties of the two polymers (named as PBQ-0F and PBQ-4F) were investigated by employing [6, 6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor and a water-alcohol-soluble polymer interlayer material (named as PFNBr) to fabricate photovoltaic devices. For the PBQ-0F:PC71BM blend, the device using Ca/Al as cathode showed very similar efficiency as the device using PFNBr/Al as cathode, while for the PBQ-0F:PC71BM blend, photovoltaic performance of the device can be distinctly improved by replacing Ca/Al with PFNBr/Al. As a result, the best PCE of the PBQ-4F:PC71BM based devices reached 9.04%, which is much higher than that of the PBQ-0F:PC71BM based devices. The results obtained from the quantum chemistry calculations and water contact angle measurements demonstrate that these two polymers are low polar materials, and also the films based on them have hydrophobic surfaces. Since PFNBr has an amphipathic structure (hydrophobic backbone and hydrophilic side chain) and the blend films of PBQ-4F:PC71BM and PBQ-4F:PC71BM have different surface energies, the PFNBr organization atop these two blend types of should be different, which will affect device photovoltaic performance.

The device with a PFNBr/Al cathode showed a similar efficiency as the device with a Ca/Al cathode for the PBQ-0F:PC71BM-based devices, while efficiency of the PBQ-4F:PC71BM-based devices was significantly improved by using PFNBr as an n-type interlayer material.Figure optionsDownload as PowerPoint slide