Multifunctional Ionic Liquid Additive Modulates Crystallization Dynamics and Phase Distribution for Inverted FA-Based Two-Dimensional Dion–Jacobson Perovskite Solar Cells with 18.24% Efficiency

Two-dimensional (2D) perovskites, renowned for their superior optical properties and environmental stability, have demonstrated significant potential in perovskite solar cells (PSCs). However, the random phase distribution and intrinsic surface and bulk defects in Dion–Jacobson (DJ) perovskites impede the charge transport dynamics. This study investigates the effect of dual additives in FA-based 2D DJ PSCs. The findings reveal that this dual-additive method significantly improves the microstructural properties, charge transport, and collection efficiency of perovskites, leading to better photovoltaic performance. BAAc-treated devices show an extended charge recombination lifetime, reduced charge extraction time, and a significant decrease in trap density, indicating reduced nonradiative recombination. Transient absorption spectroscopy and grazing-incidence wide-angle X-ray scattering study confirm that BAAc treatment reduces residual PbI2 and improves charge transfer from a low n-value phase to a 3D-like phase. Consequently, the optimized device achieves a power conversion efficiency (PCE) of 18.24%, surpassing the control device’s 16.73% and representing one of the highest PCEs for FA-based 2D DJ PSCs. Moreover, optimized devices maintain their performance over 1800 h, indicating improved storage and humidity resistance. In conclusion, the dual-additive strategy significantly improves the crystallization quality of perovskites and minimizes defect density, thereby improving the PCE and stability of the devices.