Effects of a perfluorinated compound as an additive on the power conversion efficiencies of polymer solar cells

A perfluorinated compound, 4-amino-2-(trifluoromethyl)benzonitrile (ATMB), was applied as an additive to polymer solar cells (PSCs) with P3HT [poly(3-hexylthiophene)]:PCBM [[6,6]-phenyl-C₆₁-butyric acid methyl ester] blend films. The addition of 6 wt% ATMB to a P3HT:PCBM layer led to an increased power conversion efficiency of 5.03% due to the enhanced short circuit current and fill factor when compared with that of the reference cell without an additive. On the other hand, the devices with 4-aminobenzonitrile as an additive, not containing fluorine atoms in the molecule, displayed lower PCEs than that of the reference cell. The UVvisible absorption spectra, X-ray measurements and carrier mobility studies revealed that ATMB facilitated ordering of the P3HT chains, resulting in higher absorbance, larger crystal size of P3HT and enhanced hole mobility. XPS depth profiling measurements also showed that the additive molecules were predominantly positioned in the range of 25 nm under the surface of the P3HT:PCBM film, leading to improved fill factor.