Implications of Dynamic vs. Static 2D/3D Halide Perovskite Interfaces on Solar Cell Stability

Employing a 2D perovskite or ammonium-halide salt passivation layer is a promising method to improve the stability and efficiency of halide perovskite solar cells (PSC). Recent work has revealed that the initial structure of this passivation layer may evolve during PSC aging, depending on the identity of the halide salt employed. Our work has indicated that the nature of the organic ligands that form the 2D perovskite passivation layer can also impact the operation stability of the resulting solar cells. Specific to this investigation, we have examined the structural evolution of several 2D/3D perovskite interfaces comprising different organic ligands using ex-situ photoluminescence and x-ray diffraction measurements. We found the 2D/3D perovskite interface to be “dynamic” when mono-functional ammonium ligands, i.e., butylammonium and 4-fluorophenethylammonium, are used to form the 2D perovskite layers atop the 3D perovskite, as the structure of the 2D perovskite layers evolve substantially during aging. Replacing the mono-functional ammonium ligands with a bifunctional diammonium ligand, i.e., 1,4-butanediamine, instead results in a “static” interface in which the structure of the 2D perovskite layer remains stable during aging. Given the chemical difference in the organic ligands, we ascribe the difference in stability of these 2D/3D perovskite interfaces to the extent of binding the organic ligands have with their adjacent inorganic layers within the 2D perovskites, with a greater extent of binding enhancing the structural stability of the interface.