Reversible Transformation between Cs₃Cu₂I₅ and CsCu₂I₃ Perovskite Derivatives and Its Anticounterfeiting Application

Lead halide perovskites have promising values in photoelectronic and photovoltaic applications, but the toxicity of lead is a hard barrier. Copper halide perovskite derivatives (CHPDs), as a lead-free substitution of lead halide perovskites, also exhibit excellent photoelectric properties. Here, we present a facile one-step route for the synthesis of blue-emissive Cs₃Cu₂I₅ (emission at 440 nm) and yellow-emissive CsCu₂I₃ (emission at 552 nm) CHPDs in ethanol at room temperature. Triggered by ethanol or CsI, a reversible chemical transformation accompanied by emissive color change between Cs₃Cu₂I₅ and CsCu₂I₃ CHPDs was achieved. The reversible transformation mechanism was discussed, and this transformation was employed for effective anticounterfeiting.