Nondestructive Post-Treatment Enabled by Generated 2D Perovskites Derived from Multi-ammonium Molecule Vapor for High-Performance 2D/3D Bilayer Perovskite Solar Cells.

Recently, two-dimensional (2D)/three-dimensional (3D) bilayer perovskite solar cells (PSCs) show a great potential for commercialization due to the combination of the fascinating photovoltaic performance of 3D perovskites and superior stability of 2D perovskites. However, it is a challenge to nondestructively construct 2D/3D bilayer perovskites, and the impact of the number of amine groups in ammonium spacer cations on the properties of 2D/3D bilayer perovskites has not been investigated. In this work, a novel interfacial post-treatment strategy is proposed to nondestructively fabricate 2D/3D bilayer perovskite films using the multi-ammonium molecule (MAM) vapor. Here, a series of MAMs with three to six amine groups (3 to 6N), including diethylenetriamine (DETA, 3N), triethylenetetramine (TETA, 4N), tetraethylenepentamine (TEPA, 5N), and pentaethylenehexamine (PEHA, 6N), are applied and compared. Benefiting from the strong interaction between MAMs and perovskites, the MAM vapor post-treatment can generate Dion-Jacobson (DJ) 2D capping layers on the surface of 3D perovskite films. In comparison with the 3D perovskite film, such DJ 2D/3D perovskite films exhibit improved film quality, effectively passivated defects/traps, optimized interfacial band energy alignment, and mitigatory tensile strain. In particular, the number of amine groups in MAMs can dramatically influence the quality of DJ 2D/3D bilayer perovskite films and their corresponding photovoltaic performance. As the number of amine groups increases from DETA to PEHA, the efficiency and stability of PSCs are boosted significantly. Consequently, the PEHA-based DJ 2D/3D bilayer PSC delivers a champion power conversion efficiency of 21.79% with a negligible hysteresis effect, elevated reproducibility, and enhanced device stability. This work offers the reference for designing novel and effective MAMs for nondestructively fabricating high-performance 2D/3D bilayer PSCs.