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.