Origin of the efficiency enhancement in ferroelectric functionalized organic solar cells

We have investigated the efficiency enhancement of organic solar cells upon incorporation of a thin ferroelectric polymer layer. For non-Ohmic contacts the enhancement is due to an increased open circuit voltage, which is, however, independent of the ferroelectric polarization direction. Ferroelectricity cannot play a role due to depolarization and charge compensation. The same improvement is also obtained with a non-ferroelectric fluorinated polymer. The data unambiguously show that the improved efficiency is solely due to improvement of the cathode. The fluorinated polymer layer plays the role of LiF in an optimized solar cell. (C) 2011 American Institute of Physics. [doi:10.1063/1.3587630]