Unveiling the guest effect of N-butylammonium iodide towards efficient and stable 2D-3D perovskite solar cells through sequential deposition process

Improving the stability of hybrid organic-inorganic halide perovskite materials is urgent and essential for their applications in optoelectronic devices. Here, we introduce n-butylammonium iodide (BAI) into lead-iodide crystals as guest molecules. As a result of guest effect, only a small amount BA₂PbI₄ two-dimensional (2D) perovskite (n = 1) is formed in PbI₂-BAI films. Most of BAI crystals efficiently cut and squeeze the lattice network of lead iodide. The better orientation of 2D lead iodide crystals is obtained via this guest effect. In the following sequential deposition process, that BAI re-dissolve in MAI isopropanol (IPA) solution leads to a mesoporous structure of PbI₂ and introduces a 2D perovskite (n = 2) protect layer in 3D MAPbI₃ after annealing. Finally, the morphology, crystallization and stability of CH₃NH₃PbI₃ are simultaneously improved by the insertion of BAI guest molecules. Consequently, CH₃NH₃PbI₃ PSCs with an optimized cutting behavior exhibited a power conversion efficiency of 18% and significantly improved the stability.