Revealing Mechanisms and Ultrafast Dynamics of Tetrabutyl Phosphonium Bromide Ionic Liquids Post-Treatment in CsPbBr3 Perovskite Films

All-inorganic perovskite solar cells (PSCs) have garnered significant attention due to their straightforward fabrication process and outstanding photophysical properties in the realm of optoelectronic devices. Nevertheless, the preparation and operation of perovskite solutions can introduce various defects, which adversely impact the recombination of photogenerated carriers, stability, and hamper photoelectric conversion. Consequently, enhancing perovskite stability remains a challenge in practical applications. One effective approach to improving stability involves the procedure of defect passivation for perovskite films. In this study, tetrabutylphosphine bromide ionic liquids (ILs) were chosen as passivating agents for CsPbBr3 perovskite films and the passivation mechanism was investigated systematically. A one-step spin-coating method was employed for post-treatment, aimed at minimizing defect formation and suppressing nonradiative recombination. A range of characterization techniques, including Fourier infrared transform spectroscopy, steady-state fluorescence spectroscopy, and ultrafast femtosecond transient absorption (fs-TA) spectroscopy, were employed to comprehensively investigate the carrier cooling and recombination processes in the perovskite films. The obtained results are anticipated to offer valuable insights into comprehending the passivation mechanism and the photophysical phenomena related to carrier generation and relaxation in perovskite materials following photoexcitation.