Octahedral Factor Regulation Engineering To Achieve High-Entropy Metal Halide Perovskite Alloys Incorporating Cl–, Br–, and I– at the X Site

The soft ionic nature, tunable lattice structure, variable component, and solution processability make metal halide perovskite (MHP) materials good candidates as high-entropy materials. Although composition regulation of the X site can be easily achieved by mixing two types of halogens, it remains challenging to prepare high-entropy MHP (HEMHP) with three types of halogens due to the large octahedral factor (μ) difference of [PbX6]4–. Fundamental research is explored to synthesize HEMHP incorporating Cl–, Br–, and I– via μ regulation engineering, which breaks the limitation of a 6% Cl/I ratio in perovskite to achieve 116%. Doping AlCl3 in CsPbBrI2 could successfully reduce the μ differences for [Pb1–aAlaX6](4–a)–, shorten the Pb–X bond length, and enhance the Pb–X bond energy via the Al–X covalent bond. Therefore, the crystal distortion and halogen ion migration could be inhibited to form a homogeneous HEMHP, such as Cs1.18Pb0.92Al0.08(Cl0.13Br0.51I0.36)2.45L–0.81, Cs1.12Pb0.88Al0.12(Cl0.25Br0.49I0.26)2.53L–0.71, and Cs1.06Pb0.85Al0.15(Cl0.29Br0.46I0.25)2.43L–0.78. Such μ regulation engineering method is feasible and universal to use other metal ions (Zn2+, Mn2+, and In3+) to synthesize single-phase HEMHP. Furthermore, the optical band gap and emission peak wavelength for HEMHP and MHP are linearly dependent on their lattice distances, which is the intrinsic characteristic for composition-depended perovskite.