Intraband Mid-Infrared Transitions in Ag₂Se Nanocrystals: Potential and Limitations for Hg-Free Low-Cost Photodetection

Infrared photodetection based on colloidal nanoparticles is a promising path toward low-cost devices. However, mid-infrared absorption relies on interband transitions in heavy metal-based materials, which is a major flaw for the development toward mass market. In the quest of mercury-free infrared active colloidal materials, we here investigate Ag₂Se nanoparticles presenting intraband transition between 3 and 15 μm. With photoemission and infrared spectroscopy, we are able to propose an electronic spectrum of the material in the absolute energy scale. We also investigate the origin of doping and demonstrate that it results from a cation excess under the Ag⁺ form. We demonstrate photoconduction into this material under resonant excitation of the intraband transition. However, performances are currently quite weak with (i) a slow photoresponse (several seconds) and (ii) some electrochemical instabilities at room temperature