Simultaneously, PbBr2 (69.1mg) was added to 5 mL of ODE and stirred under vacuum for 1 hour at 120 ˚C. The mixture of OA: OLAm (0.5 mL:0.5 mL) was injected into the PbBr2 solution and heated to 170 ˚C for 1 hour. Next, 0.4 mL of Cs-OA was injected, and the reaction was quenched in an ice bath. Here, the color of the solution turned green. To eliminate the ligands from the surface of the HP particles, they were washed several times with toluene with the assistance of the centrifuge at 3500 rpm for 5 min. The particles were redispersed in toluene and kept in the solution for further characterization.