A Bifunctional Colloidal Quantum Dot Diode for Nanosecond Short‐Wave Infrared Detection and Emission

Short‐wave infrared (SWIR) technologies are vital for optical communication, all‐weather imaging, and advanced spectroscopy. Using a single diode for light detection and emission can reduce device footprints, lower cost and enable fast, bidirectional communication. However, dual detection/emission operation often involves incompatible choices of material and stack design, which result in devices with inferior performance. Here, we introduce a bifunctional PbS QD diode stack that achieves, for the first time, nanosecond‐fast photodetection and emission in a single SWIR device. Using thin active layers with high charge‐carrier mobility and compact geometries, we demonstrate a record 2 ns response in photodiode (QDPD) mode and 11.7 ns rise time/6.5 ns fall time in light‐emitting diode (QDLED) mode. This high‐speed operation is combined with a 49% external quantum efficiency (EQE) and 2.6 × 10 1 2 cm·Hz 0 . 5 ·W − 1 detectivity for QDPD operation, while the QDLED reaches 8.1% EQE. These high‐speed, compact devices unify imaging and detection with a single, CMOS‐compatible platform, and set the stage for integrated SWIR photonics and bidirectional optical interconnects. This work demonstrates the potential of QDs to unify imaging, detection, and communication in a single materials platform.