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 Cs 2 MCl 6 (M=Zr 4+ , Sn 4+ , Te 4+ , Hf 4+ , Re 4+ , Os 4+ , Ir 4+ or Pt 4+ ) 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 [MCl 6 ] 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 Cs 2 MCl 6 crystal structure and stoichiometry maintained. The incorporation of various [MCl 6 ] 2- octahedral molecular orbitals disordered across high-entropy five- and six-element Cs 2 MCl 6 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.