Balancing Passivation and Charge Carrier Transport in Core/Shell Quantum Dots toward High‐Responsive and Low‐Dark Current Infrared Photodetectors

Lead selenide (PbSe) quantum dots (QDs) are promising candidates for short‐wave infrared (SWIR) photodetectors; however, their performance is fundamentally limited by surface trap states and environmental instability. Constructing core/shell heterostructures offers a potential solution, yet a critical challenge remains in optimizing the shell to strike a synergistic balance between effective defect passivation and efficient carrier transport. Herein, we report a precise cation‐exchange epitaxial growth strategy to synthesize highly monodisperse PbSe/PbS core/shell QDs with tunable shell thickness. We systematically elucidate the structure‐property relationships, revealing that thicker PbS shells significantly suppress non‐radiative recombination and extend carrier lifetimes. By tailoring the shell thickness to an optimal regime, we achieve a high‐quality QD solid that minimizes trap density while maintaining superior carrier mobility. Consequently, the optimized SWIR photodetector exhibits a high external quantum efficiency (EQE) of 49% at 0 V and a specific detectivity of 2.37 × 10 12 Jones at 1650 nm. Furthermore, this robust architecture enables the extension of spectral response into the extended SWIR region (up to 2.5 µm) and facilitates the demonstration of high‐resolution SWIR imaging. This work provides a generic design principle for engineering high‐performance infrared optoelectronics through precise modulation of heterostructure nanomaterials.