Optimized Crystallization via Ionic Liquid Engineering for Air-Fabricated Perovskite Solar Cells with Efficiency of 25.11%

The premature reaction of PbI₂ with organic cations in perovskite (PVK) precursor solutions often leads to compromised film quality. To mitigate this, the ionic liquid (IL) pyridinium trifluoromethanesulfonate is introduced into the precursor solution. The strong interaction between pyridinium trifluoromethanesulfonate and PbI₂ promotes the formation of nucleation clusters, effectively lowering the nucleation barrier and regulating the crystallization of perovskite, resulting in high-quality, homogeneous PVK films. In situ characterization shows that the prenucleation strategy yields PVK films with an average grain size exceeding 1 μm. The hydrophobicity of the trifluoromethyl group modulates humidity, facilitating perovskite crystallization in moist environments. This is in contrast to the typical negative effects of moisture, which can induce defects in perovskite structures. As a result, IL-modified perovskite solar cells (PSCs) achieved a remarkable power conversion efficiency (PCE) of 25.11% under ambient conditions. These PSCs retained 80.43% of their initial PCE after 820 h of continuous maximum power point (MPP) tracking. Furthermore, after 1000 h of exposure to air with 30%–50% relative humidity (RH) at room temperature, the devices maintained 87% of their initial efficiency, demonstrating excellent air stability for long-term PSC applications.