Deciphering the Orientation of the Aromatic Spacer Cation in Bilayer Perovskite Solar Cells through Spectroscopic Techniques

Slowing the degradation of perovskite-based solar cells (PSCs) is of substantial interest. We engineered the surface by introducing a hydrophobic overlayer on a three-dimensional (3D) perovskite using fluorinated or nonfluorinated aryl ammonium cation spacers. The placement of a fluoroarene cation allows the formation of a bilayer structure, that is, layered/3D perovskites. By doing so, the surface hydrophobic character increases notably by the virtue of the perfluorinated benzene moiety. The fabricated devices thereof gave higher performance and longevity than control devices in addition to boosting reliability. The fluorophenethylammonium iodide (FPEAI)-based devices showed lower nonradiative carrier recombination. To decipher the orientation of the spacer cation in this bilayer structure, we probed the surface by polarization-modulated infrared reflection-absorption spectroscopy and noted substantial differences in the orientation due to the presence of fluorine substitution. We hypothesize that the stronger van der Waals interactions due to the higher electronegativity in FPEAI govern the orientation and performance enhancement and act as a barrier to moisture decomposition.

Automated summary

In this study, the surface of 3D perovskite was engineered by introducing fluorinated or nonfluorinated aryl ammonium cation spacers, leading to improved performance and longevity of perovskite-based solar cells. The use of fluorophenethylammonium iodide (FPEAI) also showed lower nonradiative carrier recombination, indicating higher reliability and efficiency. The presence of fluorine substitution resulted in notable differences in orientation, with stronger van der Waals interactions playing a key role in governing orientation and performance enhancement.