Revealing the Roles of Guanidine Hydrochloride Ionic Liquid in Ion Inhibition and Defects Passivation for Efficient and Stable Perovskite Solar Cells

As a result of full-scale ongoing global efforts, the power conversion efficiency (PCE) of the organic-inorganic metal halide perovskite has skyrocketed. Unfortunately, the long-term operational stability for commercialization standards is still lagging owing to intrinsic defects such as ion migration-induced degradation, undercoordinated Pb2+, and shallow defects initiated by disordered crystal growth. Herein, we employed multifunctional, non-volatile tetra-methyl guanidine hydrochloride [TMGHCL] ionic liquid (IL) as an additive to elucidate defects' passivation effects on organic-inorganic metal halide perovskite. More specifically, the formation of hydrogen bonds between H+ in GA+ and I- and coordinate bonding between Cl- and undercoordinated Pb2+ could significantly passivate these defects. The hypothesis was confirmed by both experimental and DFT simulations displaying that the optimized ratio of IL integration restrains ion migration, improving grains' size, and significantly elongating the carrier lifetime. Remarkably, the modified cell achieved a peak efficiency of 22.00 % with negligible hysteresis, compared to the control device's PCE of 20.12 %. In addition, the TMGHCL-based device retains its 93.29 % efficiency after 16 days of continuous exposure to air with a relative humidity of 35 +/- 5% and temperature of 25 +/- 5 degrees C. This efficient approach of adding IL to perovskites absorber can produce high PCE and has strong commercialization potential. A multifunctional guanidine-based ionic liquid (TMGHCL) was successfully employed as an effective passivation agent to the organic-inorganic metal halide perovskite precursor. TMGHCL formed the strong interactions with perovskite through H atoms of GA+ cations with the halogen in perovskite and Cl- anion with Pb2+ in perovskite. This effectively prevents the ion migration, reduces unreacted PbI2, and facilitates crystal growth, achieving the high-quality perovskite films and high-performance devices. As a result, the IL-modified devices achieved an improved PCE of 22 % from 20 % while retaining 93.29 % of its peak efficiency after continuous operation for 16 days. image