Toward High-Entropy Halide and Chalcohalide Semiconductors for Photocatalysis

High-entropy design has expanded from metallic alloys to compositionally complex oxides, chalcogenides, and, more recently, halide semiconductors. By distributing several elements over one or more crystallographic sublattices, this strategy can generate properties that are inaccessible through conventional dilute doping, including nonlinear bandgap tuning, modified defect chemistry, lattice distortion, and enhanced chemical stability. Moreover, configurational entropy should be thought not only in terms of compositional variation (alloying) but also in terms of different microstructural polymorphisms and engineered disorder. Metal halide perovskites and perovskite-inspired materials offer unusually broad compositional and structural spaces, yet high-entropy design has only started to be investigated in these systems. Metal chalcohalides provide an equally promising and largely unexplored platform, combining the electronic diversity of halides with the stronger bonding and frequently superior water stability of chalcogenides. In this Perspective, we first discuss how the term high-entropy should be applied in the realm of multinary semiconductors. Then, we identify promising compositional spaces for high-entropy halides and chalcohalides and evaluate synthetic strategies to achieve them experimentally, including automated combinatorial routes and non-standard mechanochemical synthesis. Eventually, we examine the potential of these emerging materials in photocatalytic applications. The Perspective ends by discussing current bottlenecks and potential routes for the development of this emerging field.