Controllable synthesis of CsxPbyBrz-based perovskites by a polar solvent-triggered transformation method and its application as an invisible security ink

Recently, all-inorganic CsPbX3 (X = Cl, Br, I) perovskites have become one of the most promising candidates for photoelectronic and photovoltaic applications. Herein, we report the controllable synthesis of CsxPbyBrz-based perovskites by a simple polar solvent-triggered (H2O, CH3OH) chemical transformation method. The phase of CsxPbyBrz-based perovskites can be successfully converted from Cs4PbBr6 to CsPbBr3 by using H2O as a polar solvent and from CsPbBr3 to CsPb2Br5 by using CH3OH as a polar solvent, and this method can also be applied to synthesize Cs4PbBr6/CsPbBr3 and CsPbBr3/CsPb2Br5 composites by controlling parameters of transformation process. Moreover, a novel kind of encryption and decryption technology is developed based on the characteristics that the white Cs4PbBr6 reacts with H2O to rapidly produce yellow CsPbBr3, using the Cs4PbBr6 toluene solution as the invisible security ink and H2O as the decryption key. Our results present a controllable route to realize transformation from Cs4PbBr6 to CsPbBr3 and from CsPbBr3 to CsPb2Br5.