Buried interface modification by multifunctional ionic liquids for triple-cation perovskite solar cells made in a fully ambient air

Abstract

Triple-cation CsFAMA perovskite solar cells (PSCs) have gained great attention because of their excellent stability. Buried interface management is one of the most effective methods to further improve device performance; however, such a strategy has not been extensively studied in air-processed triple-cation PSCs. Herein, we report an effective management strategy that incorporates ionic liquids (ILs) of 1-butyl-3-methylimidazole hexafluorophosphate (BMIMPF₆) to modify the buried interface. The synergistic effect of BMIMPF₆ is revealed by employing several characterization methods, including time-of-flight secondary ion mass spectrometry and inductively coupled plasma mass spectrometry. It was found that BMIMPF₆ can significantly coordinate with Sn⁴⁺ and fill the oxygen vacancy defects from one side of the electron transport layer, and simultaneously bond with uncoordinated Pb²⁺ from the other side of the perovskite layer, leading to reduced nonradiative recombination losses and enhanced carrier extraction. More importantly, such an IL “bridge” enabled BMIMPF₆ to exist at the buried interface, which avoids damage to the passivating layer in the next spin-coating process for achieving the perovskite film. Moreover, BMIMPF₆ also penetrates the perovskite film and regulates the crystallinity of perovskite. As a result, the BMIMPF₆-modified device fabricated in ambient air without glove boxes or dry rooms delivers a champion power conversion efficiency (PCE) of 21.74%. The unencapsulated device maintains 77.5% of its initial PCE after being stored in ambient air for more than 3500 h. Additionally, the lead leakage rate from the perovskite film is reduced. This work provides a facile and low-cost method to fabricate high-performance all-air-processed PSCs.