Purification of the Perovskite Nanoplates: to purify these materials we cannot make use of antisolvents because nanoplates are sensitive to even mildly polar solvents. We, thus, centrifuge the crude solution after the completion of the reaction at 13.500 rpm for 10 minutes. A pellet of material is deposited on the bottom of the tube after the centrifuge step. The supernatant is discarded, the global yield is measured, and the pellet is resuspended in anhydrous hexane to give a ~20 mg/mL suspension. This hexane suspension is then kept in a fridge at 5 °C overnight. For CsPbI3, a new centrifuge step is necessary to precipitate some remaining insoluble materials. For the second centrifuge, though, the supernatant is kept and the solid on the bottom of the centrifuge tube is discarded (note that it will change the initial concentration). The supernatant is then filtered in a hydrophobic syringe filter with 22-µm pore. The filtered suspensions are kept refrigerated and sealed under N2 atmosphere until their use.