Suppressed Halide Ion Migration in 2D Lead Halide Perovskites

Two-dimensional (2D) lead halide perovskites represent an emerging class of materials given their tunable optoelectronic properties and long-term stability in perovskite solar cells. In order to assess the halide ion mobility, we have tracked the changes in the bromide and iodide composition in physically paired 2D lead halide perovskite films of different layer numbers (n = 10-1). These low-dimensional perovskites suppressed halide ion migration as a result of their intercalated spacer ligands and their strong van der Waals interactions. The rate constants for halide exchange of low dimensionality perovskites follow the Arrhenius relationship with thermal activation energy ranging from 58 kJ/mol (n = 10) to 72 kJ/mol (n = 1). The suppression of halide ion mobility (and diffusion coefficient) with modulating perovskite layer number (n) provides further insight into the role of 2D perovskites in improving the performance of photovoltaic devices.