Exploration of two highly fluorinated ammonium cations as spacers in low- and mixed dimensional hybrid lead iodide perovskites

We here report the synthesis of 2D perovskites based on highly fluorinated organic cations (LF8 and SMS28) that impart high hydrophobicity and thermal stability to the resulting materials. Stability tests showed that 2D perovskites (SMS28)2PbI4and (LF8)2PbI4maintained their structural properties unchanged for over a month of exposure to 75% relative humidity (RH), demonstrating high resistance to severe environmental conditions. When applied as top layers on films of a typical 3D perovskite (MAPbI3) employed in photovoltaic cells, these fluorinated 2D materials slowed down the structural deterioration processes triggered by water infiltration as compared to unprotected samples, even at high RH conditions. The results highlight the potential of these coatings as a hydrophobic barrier to increase the environmental stability of common 3D perovskites, offering the possibility of improving the long-term protection of moisture-sensitive materials.