Mosaic CuI−CuII−InIII2D Perovskites: Pressure‐Dependence of the Intervalence Charge Transfer and a Mechanochemical Alloying Method

Abstract

AbstractThe perovskite (BA)4[CuII(CuIInIII)0.5]Cl8(1BA; BA+=butylammonium) allows us to study the high‐pressure structural, optical, and transport properties of a mixed‐valence 2D perovskite. Compressing1BAreduces the onset energy of CuI/IIintervalence charge transfer from 1.2 eV at ambient pressure to 0.2 eV at 21 GPa. The electronic conductivity of1BAincreases by 4 orders of magnitude upon compression to 20 GPa, when the activation energy for conduction decreases to 0.16 eV. In contrast, CuIIperovskites achieve similar conductivity at ≈50 GPa. The solution‐state synthesis of these perovskites is complicated, with more undesirable side products likely from the precursor mixtures containing three different metal ions. To circumvent this problem, we demonstrate an efficient mechanochemical synthesis to expand this family of halide perovskites with complex composition by simply pulverizing together powders of 2D CuIIsingle perovskites and CuIInIIIdouble perovskites.