Supporting Information for Trapping & De-trapping in Colloidal Perovskite Nanoplatelets: Elucidation and Prevention of Nonradiative Processes through Chemical Treatment

Precursor solution preparation: A Cs-oleate precursor solution was prepared by dissolving Cs2CO3 (0.1 mmol) in oleic acid (10 mL) at 100 ◦C.S1 A PbBr2 treatment precursor solution was prepared by dissolving PbBr2 (0.1 mmol) in a mixture of oleic acid (0.1 mL), oleylamine (0.1 mL) and hexane (10 mL) at 100 ◦C. A PbBr2 synthesis precursor was prepared by dissolving PbBr2 (0.1 mmol) in a mixture of oleic acid (0.1 mL), oleylamine (0.1 mL) and toluene (10 mL) at 100 ◦C. All mixtures were vigorously stirred and heated in order to dissolve the salts, after which transparent, colorless precursor solutions were obtained.