Study on the preparation of Ag2Se colloidal quantum dots and its infrared properties

Quantum dots infrared photodetector (QDIP) has found important applications due to its many advantages, such as long effective carrier life, low dark current, high operating temperature, facile preparation and low cost. In recent years, infrared photodetectors consisting of PbS and HgTe colloidal quantum dots (CQDs) have reported breakthroughs in the detection of short-wave infrared (SWIR) and mid-wave infrared (MWIR) demonstrating detectivity of 1×10¹³ Jones and 1×10¹¹ Jones, respectively. However, these materials contain Pb and Hg elements, which are harmful to human and the environment. Therefore, the development of non-toxic quantum dot materials is highly desirable for QDIP. In this work, Ag₂Se CQDs were studied for use in infrared photodetector. The novel CQDs have the advantages of low toxicity, good infrared optical properties, which can obtain adjustable infrared absorption due to its small bulk band gap of 0.15 eV, and biocompatibility etc. The Ag₂Se CQDs were prepared by hot injection method and were characterized by Transmission Electron Microscope (TEM), X-ray Diffraction (XRD), Fourier Transform Infrared spectrum (FTIR), Atomic Force Microscope (AFM) and X-ray Photoelectron Spectroscopy (XPS). These Ag₂Se CQDs demonstrated good monodispersion, size uniformity and crystallization. Interestingly, the exciton peak appeared in the infrared band of 3-4 μm. Subsequently, Ag₂Se CQDs photodetector was produced by spin coating the CQDs onto a 5 μm interdigital electrode. The device exhibited a low dark current of 1.3×10⁻⁶ mA with responsivity of 5 A/W and detectivity of 1.5×10¹³ Jones. The results of this work show that Ag₂Se CQDs are expected to have potential applications in QDIP.