The mid-to-far-infrared wave is an electromagnetic wave with a wavelength range of 5 − 1000 μm, significant for remote sensing, object identification, chemical sensing, missile defence, and weather monitoring. Various methods provide dual infrared band detection; however, their high cost, complexity, and requirement for active cooling hinder broad implementation. This study utilises the benefits of colloidal quantum dot composite for the advancement of dual-wave infrared band detectors. We present the structural, compositional, morphological, spectroscopic, and electrical characteristics of colloidal Ag₂S/PbS quantum dot (CQD) composites. The carrier concentration value 2.032 \(\times\) 1020 cm⁻3 from capacitance–voltage measurement was determined and it aligns with the carrier concentration derived from the Hall measurement. The fabricated ITO/Ag₂S + PbS/Ag photodetector device yielded a photocurrent density 0.04 mA/cm2 under dark condition and 0.24–34 mA/cm2 under 980 nm to 15 μm wavelength illumination respectively, resulting in increased photocurrent relative to dark current at room temperature. This configuration promotes a double Schottky barrier with an ideality factor of 1.01, indicative of optimal Schottky behaviour in photodiodes. The figure of merit sensitivity (S%), photo responsivity (R), and D* are 48%, 9.64 mA/W, and 2.5 × 109 Jones, respectively. The external quantum efficiency (EQE%) measured at -10 °C, 0 °C, and 10 °C is 52.7%, 34.9% and 12.2%, respectively, facilitating the design of photodetector which can work at both low and room temperature using a dual-band IR active device. The outcomes of this FOM are influenced by characteristics such as quantum dot size, temperature, and the concentration percentage of Ag₂S.
