Enhanced chemical interaction between ionic liquid and halide perovskite to improve performance of perovskite solar cells

Perovskite solar cells (PSCs) with wide bandgap (Eg > 1.67 eV) metal halides combined with silicon solar cells for tandem photovoltaics are one of the most promising technologies for achieving efficiencies over 33 %. However, low long-term stability of PSCs due to deep trap states and halide segregation in the perovskites impedes commercialization. Ionic liquids have been widely used to overcome this drawback, with anions primarily interacting with the perovskite and cations playing a more limited role. Here, by giving cations functional groups that bind to the perovskite and passivate defects, both cations and anions in the ionic liquid are designed to improve the quality of the perovskite thin film. The incorporation of a methoxy group within the cation fosters interaction with lead cations in the perovskite structure. This interaction enhances passivation at the interfaces, thereby suppressing ion migration and leading to improved optoelectronic properties. PSCs fabricated with the wide-bandgap perovskite containing 1-(2-methoxyethyl)-1-methylpiperidinium thiocyanate (MMP-SCN) exhibit higher power conversion efficiency (PCE) and long-term stability against light, heat, and moisture than those containing 1-butyl-1-methylpiperidinium thiocyanate (BMP-SCN). PSCs with MMP-SCN achieve PCEs over 20% with FF of over 84% and demonstrate long-term operational stability of 1000 h.