Solvent-mediated carboxylic acid diammonium spacer for synthesizing FA-based 2D Dion–Jacobson perovskites toward efficient solar cells

Two-dimensional (2D) perovskites are promising for photovoltaic applications due to their outstanding optical properties and better environmental stability compared to three-dimensional (3D) perovskites. Unlike 2D Ruddlesden–Popper (RP) perovskites, which use monovalent ammonium spacers, Dion–Jacobson (DJ) perovskites employ divalent organic spacers that enhance structural stability by mitigating weak van der Waals interactions. However, the random phase distribution and disorder crystal orientation in 2D DJ perovskites create deep quantum wells, hindering charge transfer and reducing short-circuit current density (JSC) and overall photovoltaic performance. This study introduces an organic diammonium, 1,4-butanediamine diacetate (BDAAc2), to replace the traditional halide spacer 1,4-butanediamine iodide (BDADI2). This substitution regulates perovskites crystallization dynamics, reducing compositional disorder and random phase distribution, thus improving the quality of the perovskite films. The robust coordination interactions between BDAAc2 and the perovskite inorganic framework lead to an ordered [PbX6]4− arrangement, suppressing the formation of complex intermediate phases and significantly enhancing δ phase crystallinity in the intermediate film. This results in a high yield of high-quality α phase. Consequently, the resulting 2D DJ perovskite solar cells based on BDAFA3Pb4(I0.9Br0.1)13 achieve a higher power conversion efficiency of 16.41% and an elevated JSC of 20.46 mA cm−2.