Recent advances in lead-free Cs2ZrCl6 metal halide perovskites and their derivatives: From fundamentals to advanced applications

Zero-dimensional (0D) lead-free metal halide perovskites (MHPs) have attracted increasing attention owing to their intriguing emission properties (e.g., large Stokes shifts, extremely broadband emission, and high color rendition). Among various MHPs, Cs2ZrCl6 possesses several keys to commercialization such as low cost, environmental friendlies, flexible synthesis methods, high chemical yields, and high photoluminescence quantum yield (PLQY). Cs2ZrCl6 and its derivatives exhibit easily modulated self-trapping exciton (STEs) emission, dopant-induced photoluminescence, and thermally activated delayed fluorescence (TADF), which have become a research hotspot. In this review, we summarize the recent experimental developments and photophysical mechanisms on Cs2ZrCl6 and their derivates. Firstly, the intrinsic structural and optical properties of Cs2ZrCl6 are discussed in detail, followed by summarizing synthesis methods and discussing stability. We also highlight strategies to manipulate optical properties through crystal site substitution, including ns2 and rare earth (RE) ions doping, and energy transfer. Moreover, organic cations replacements in the A-site of Cs2ZrCl6 is another choice to extend the optical properties. The versatile optical properties of Cs2ZrCl6 and the derivatives allow for several emerging applications including human-centric lighting, X-ray imaging, etc. This review aims to provide a roadmap for the future development of Cs2ZrCl6-based MHPs, as well as guidance for structural manipulation and emission design of other MHPs suitable for practical applications.