Quantum‐Cutting Yb ³⁺ ‐Doped CsPbCl ₃ Perovskite Materials: From Synthesis and Mechanisms to Optoelectronic Applications

Yb 3+ ‐doped CsPbCl 3 nanocrystals (NCs) represent the most efficient quantum‐cutting system, converting one UV photon into two NIR photons. This material uniquely combines an ultra‐large Stokes shift (>550 nm), a PLQY exceeding 100%, and narrow‐band 980 nm emission. These characteristics directly address persistent device‐level bottlenecks, including self‐absorption in scintillators, interlayer crosstalk in stacked multi‐energy X‐ray detectors, and the low utilization efficiency of UV photons in c‐Si photovoltaics. In this review, we compare various syntheses with respect to doping efficiency, site selectivity, and scalability, and reveal that none achieves site‐selective doping. We trace the evolution of the two‐step versus cooperative one‐step energy‐transfer debate from 2017 to the most recent atomic‐scale tomographic evidence, showing that while the cooperative model is now favored, atomic‐scale findings reveal that Yb 3+ occupies both substitutional and interstitial sites, not just substitutional sites as previously assumed. This uncontrolled coexistence of different sites directly impacts device performance, because the specific site occupied by Yb 3+ determines energy‐transfer efficiency. This central issue runs through all applications. Therefore, for each application, we identify the device‐level requirement that it uniquely meets, summarize the reported performance, and highlight the remaining challenges. Finally, we provide an outlook that links current bottlenecks to future research directions.