Structural Evolution of Perovskite Nanoplatelets in Polar Solvents

Tuning the absorption and emission properties of two-dimensional (2D) metal halide perovskites with layer numbers and halide composition offers a convenient way to utilize these materials in optoelectronic applications. When prepared as a colloidal suspension in toluene, these 2D nanoplatelets (NPLs) exhibit good stability. However, introduction of even a small amount of polar solvent (e.g., isopropanol) causes the NPLs to grow into a greater number of layered NPLs, eventually leading to bulk nanostructures. By controlling the addition of a polar solvent, we have now resolved the growth of NPLs from n = 2 to n = 3, 4, and >4 over an extended period of ripening. The energy transfer that occurs between higher bandgap NPLs (lower n) and lower bandgap NPLs (higher n) within the same suspension is analyzed using time-resolved transient absorption spectroscopy. The funneling of energy transfer between different layers outcompetes the excitonic recombination process, thus increasing the emission yield and lifetime.