Stability Enhancement of Ambient Fabricated Perovskite Film Using Ionic Liquid Dopant

The stability of the perovskite film is a crucial factor that challenges the commercialization of Perovskite solar cells (PSCs). It can be affected by factors such as moisture, oxygen, light, and temperature. Another critical factor in the fabrication of PSCs is the ability to deposit the perovskite film in ambient conditions rather than in an inert atmosphere (N₂). To address these issues, this study aims to improve the stability of the perovskite film by adding ionic liquid, such as 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) and 1,3-dimethyl-3-imidazolium hexafluorophosphate (DMIMPF₆ ), to the perovskite precursor using a two-step deposition method in ambient air. The degradation of the perovskite film was observed under high relative humidity (around 70-80% RH) without encapsulation.<br/>Results from UV-visible spectroscopy showed that the best stable perovskite film with the BMIMBF₄ ionic liquid additive achieved 144 hours of α phase perovskite film without changing absorbance and also prolonged the perovskite structure for over 240 hours before being entirely degraded into the undesirable δ phase. DMIMPF₆ also showed potential for longer stability than the control film without an ionic liquid additive and could be doped into both the PbI₂ layer (step one) and the FAI/MAI layer (step two). Adding ionic liquids also improved the hydrophobicity of the perovskite film. X-ray diffraction results showed that the film with an ionic liquid dopant could suppress residual PbI₂ compared to the one without an ionic liquid. Overall, this study presents promising results for the large-scale fabrication of stable PSCs.