Unraveling the Role of Triiodides in Halide Precursors for Facile Anion Exchange in Lead Halide Perovskite Nanocrystals

Iodine and oleylamine react to form oleylammonium iodide, which is the most widely used iodide source for the anion-exchange reaction in lead halide perovskite nanocrystals (LHP NCs). The Lewis acid-base properties of iodine and oleylamine inevitably result in the formation of a charge-transfer complex between the oleylamine and iodine redox systems, including iodine, iodide, and triiodide ions. Herein, we demonstrate for the first time that triiodide ions hinder anion-exchange activities by monitoring the extent of anion exchange in LHP at various triiodide concentrations. Additionally, we observe that the presence of triiodide results in the formation of LHP NCs with a low photoluminescence quantum yield as triiodide consumes iodide. Finally, we propose a facile and efficient method for minimizing the concentration of triiodide in the precursor solution; heating the precursor solution facilitates fast iodide conversion, thereby decreasing the triiodide concentration. As a result, anion-exchange LHP NCs with a high photoluminescence quantum yield can be obtained with high efficiency.