High-entropy halide perovskite single crystals stabilized by mild chemistry

Although high-entropy materials are excellent candidates for a range of functional materials, their formation traditionally requires high-temperature synthetic procedures of over 1,000 °C and complex processing techniques such as hot rolling^1-5. One route to address the extreme synthetic requirements for high-entropy materials should involve the design of crystal structures with ionic bonding networks and low cohesive energies. Here we develop room-temperature-solution (20 °C) and low-temperature-solution (80 °C) synthesis procedures for a new class of metal halide perovskite high-entropy semiconductor (HES) single crystals. Due to the soft, ionic lattice nature of metal halide perovskites, these HES single crystals are designed on the cubic Cs₂MCl₆ (M=Zr⁴⁺, Sn⁴⁺, Te⁴⁺, Hf⁴⁺, Re⁴⁺, Os⁴⁺, Ir⁴⁺ or Pt⁴⁺) vacancy-ordered double-perovskite structure from the self-assembly of stabilized complexes in multi-element inks, namely free Cs⁺ cations and five or six different isolated [MCl₆]^2- anionic octahedral molecules well-mixed in strong hydrochloric acid. The resulting single-phase single crystals span two HES families of five and six elements occupying the M-site as a random alloy in near-equimolar ratios, with the overall Cs₂MCl₆ crystal structure and stoichiometry maintained. The incorporation of various [MCl₆]^2- octahedral molecular orbitals disordered across high-entropy five- and six-element Cs₂MCl₆ single crystals produces complex vibrational and electronic structures with energy transfer interactions between the confined exciton states of the five or six different isolated octahedral molecules.