Defect Passivation with Multifunctional Fluoro-Group-Containing Organic Additives for Highly Efficient and Stable Perovskite Solar Cells

Passivation of defects with functional organic molecules is one of the best strategies to improve the efficiency and stability of perovskite solar cells (PSCs). Herein, two fluorinated organic additives have been utilized to passivate the CH3NH3PbI3 perovskite film and study their effects on PSC device performance. The two additives, pentafluoropropionic acid (PFPA) and heptafluorobutanoic acid (HFBA), contain a single carboxylic acid and varying fluoro functional groups. The interaction of these additives with the perovskite was first confirmed by the density functional theory and X-ray photoelectron spectroscopy, and thereafter, PSCs with a p-i-n architecture were fabricated with and without the additives. The champion device has displayed power conversion efficiency of over 20% for the PFPA-modified perovskite. Furthermore, the improvement in charge transport and reduced recombination as a result of the passivation of defects in perovskite are well-studied using various photophysical and impedance studies. Lastly, significant enhancement in ambient stability compared to the pristine device without any additive is observed with the incorporation of fluorinated additives.