Interfacial\nModification via a 1,4-Butanediamine-Based\n2D Capping Layer for Perovskite Solar Cells with Enhanced Stability\nand Efficiency

Organic–inorganic\nperovskites face the issues of being vulnerable\nto oxygen and moisture and the trap sites located at the surface and\ngrain boundaries. Integration of two-dimensional (2D) perovskites\nas a capping layer is an effective route to enhance both photovoltaic\nefficiency and environmental stability of the three-dimensional (3D)\nunderlayer. Here, we employ 1,4-butanediammonium diiodide (BDADI),\nwhich has a short chain length and diammonium cations, to construct\na 3D/2D stacking perovskite solar cells (PSCs). The introduction of\nBDA²⁺ could passivate surface defects in 3D perovskites\nby forming 2D Dion–Jacobson (DJ) phase perovskites and effectively\nsuppressing nonradiative recombination, thus resulting in a longer\ncarrier lifetime. The DJ 2D capping layer also regulate the energy\nlevel arrangement, enabling a better charge extraction and transport\nprocess. In addition, the water-resistance ability of 3D perovskite\ngets improved because of the hydrophobic characteristic of 1,4-butanediammonium\ncations. Consequently, the 3D/2D stacking PSCs yield an energy conversion\nefficiency of 20.32% in company with the enhanced long-term stability.