Universal Homojunction Design for Colloidal Quantum Dot Infrared Photodetectors

Abstract Due to the appeal of room temperature operation and low‐cost potential, colloidal quantum dots (CQDs) have become an alternative to traditional epitaxial materials for infrared photodetection. However, various device structure designs and different functional material layers are required to obtain high photodetection performances for different infrared subranges. In this work, a straightforward method is introduced for building CQD p‐i‐n homojunction as well as the inverted n‐i‐p homojunction photodetector, by preparing various doping type and density CQD inks with a mixed phase ligand exchange method. It is approved that both normal and inverted homojunctions show the specific detectivity D * as high as 10 12 ‐10 11 Jones and external quantum efficiency near 90% at high operating temperature. It is also approved that the method works for multiple infrared subranges such as 1.5 µm that covers the conventional wavelength for fiber‐optical communication (1530–1565 nm), 1.3–1.9 µm that is about the short‐wave infrared (SWIR), 1.3–2.5 µm that covers extend SWIR (beyond the standard InGaAs sensors, 1.75 µm), and 3.6 µm that belongs to mid‐wave infrared (MWIR). Applications such as spectrometer and infrared imager are also demonstrated.