A method for forming CsPbBrz perovskite nanocrystals into a two-dimensional (2D) nanosheet includes providing CsPbBrz perovskite nanocrystals; mixing the CsPbBr? per ovskite nanocrystals into a mixture of a first solvent and a second solvent, to form a solution of the CsPbBrz perovskite nanocrystals, the first solvent, and the second solvent; and forming an optoelectronic device by patterning the CsPbBrz perovskite nanocrystals into a nanosheet, between first and second electrodes. The first solvent is selected to evaporate before the second solvent.