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 [PbX 6 ] 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 AlCl 3 in CsPbBrI 2 could successfully reduce the μ differences for [Pb 1– a Al a X 6 ] (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 Cs 1.18 Pb 0.92 Al 0.08 (Cl 0.13 Br 0.51 I 0.36 ) 2.45 L – 0.81, Cs 1.12 Pb 0.88 Al 0.12 (Cl 0.25 Br 0.49 I 0.26 ) 2.53 L – 0.71, and Cs 1.06 Pb 0.85 Al 0.15 (Cl 0.29 Br 0.46 I 0.25 ) 2.43 L – 0.78 . Such μ regulation engineering method is feasible and universal to use other metal ions (Zn 2+, Mn 2+, and In 3+ ) 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.