Pyrrolidinium Derivative‐Based Ionic Liquid Achieves Defect Passivation for Efficient Perovskite Solar Cells Exceeding 23%

In the rapidly developing field of photovoltaics, organic–inorganic metal halide perovskites are outstanding for their exceptional power conversion efficiencies (PCE), exceeding 26%. However, the full potential of these materials is often undermined by the prevalence of defects within their structure and at the grain surfaces, leading to significant nonradiative recombination losses. To meet this critical challenge, this study introduces a novel strategy involving a pyrrolidinium derivative and tetrafluoroborate ionic liquid, specifically 2‐pyrrolidin‐1‐ium‐1‐ethylammonium tetrafluoroborate (PyE(BF 4 ) 2 ), as an additive in the perovskite precursor. This approach aims to meticulously control crystallization processes and effectively passivate defects on the surface and grain boundaries of the perovskite. The formation of N─H…I − hydrogen bonds and strong ionic interactions, PyE(BF 4 ) 2 not only stabilizes the [PbI 6 ] 4− framework but also optimizes the valence band alignment with the hole transport layer. Empirical results demonstrate that perovskite solar cells modified with PyE(BF 4 ) 2 have achieved a notable PCE of 23.80% and remarkable stability exceeding 1300 h under standard testing protocols (ISOS‐V‐1). The findings emphasize the transformative potential of multifunctional ionic liquids in enhancing the performance and durability of perovskite‐based photovoltaic devices, marking a significant step forward in pursuing sustainable and efficient solar energy solutions.