<p>Colloidal quantum dot-based short-wave infrared (SWIR) photodetectors are often limited by surface traps and high noise levels at room temperature. In this work, we present a low-temperature chemical bath deposition (CBD) strategy to grow a heterojunction passivation layer on HgTe quantum dot (QD) photoactive layers, enabling high-performance SWIR photodetection at room temperature. The CBD process achieves interfacial modification through a dual mechanism: sulfur ions penetrate the HgTe QD surface to form an Hg-S bonded interfacial region while simultaneously reacting with Cd²⁺ in the bath to create a CdS electron-accepting layer, resulting in a compositionally graded CdS/Hg-S/HgTe structure. The resulting interfacial improvement, coupled with energy level modification, facilitates carrier separation and passivates surface defects, thus simultaneously enhancing the responsivity and reducing noise current of photodetectors. As a result, the phototransistor based on the CdS/HgTe photoactive layer demonstrates a high room-temperature specific detectivity of 4.43&#xa0;×&#xa0;10¹¹ Jones at 1550&#xa0;nm and maintains detectivity around 10¹⁰ Jones at extended wavelengths up to 2500&#xa0;nm. These results underscore the importance of interfacial engineering in colloidal QDs-based photodetectors and demonstrate CBD as a scalable, silicon-compatible passivation approach for achieving cryogen-free SWIR optoelectronic devices.</p> Graphical abstract <p></p>