Multifunctional Guanidine Ionic Liquid with Lactate Anion-Assisted Crystallization and Defect Passivation for High-Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) are receiving tremendous attention among other photovoltaic devices for their high power conversion efficiency (PCE), facile fabrication technique, eco-friendliness, and low cost. Unfortunately, the intrinsic defects and the quality of the perovskite films arising from the halide ion migration and undercoordinated Pb²⁺ are still considered to be the bottleneck for long-term operational stability. Herein, the introduction of task-specific ionic liquid (IL) tetramethylguanidine lactate (GuLAC) demonstrates excellent defect passivation effects and crystal growth. More specifically, the formation of hydrogen bonds between –NH₂ in GA⁺ and I^– passivates cation defects, while strong chemical interaction of lactate anion passivates the undercoordinated Pb²⁺. Both experimental observations and theoretical simulation confirm the strong interaction of GuLAC with the perovskite, which is responsible for restricting ion migration, improving grains’ size, and elongating the carrier lifetime. As a result, the IL-modified device exhibits improved PCE and superior long-term stability compared to the control device. The incorporation of IL additives proves to be a viable approach for achieving both high PCE and stable PSC devices.