Colloidal quantum dot photodetectors with 10-ns response time and 80% quantum efficiency at 1,550 nm

Fast and sensitive infrared (IR) photodetection is of interest for depth imaging that is fundamental to machine vision, augmented reality, and autonomous driving. Colloidal quantum dots (CQDs) are appealing candidates for this goal: in contrast with III–V semiconductors, they offer facile tuning of IR absorption and enable ease of integration via solution processing. So far, the best short-wave IR CQD photodetectors have been limited to 70-ns response time and quantum efficiency of 17% at 1,450 nm. To advance the field using CQDs, large-diameter CQDs are needed that combine passivation with efficient charge transport. Here, we report an efficient ligand-exchange route that tailors the halide passivants and introduces an added exchange step crucial to efficient passivation, removal of unwanted organics, and charge transport. In devices, the CQD solids give rise to external quantum efficiency greater than 80% at 1,550 nm, a measured detectivity of 8 × 10¹¹ Jones, and a 10-ns response time. The realization of fast and sensitive infrared (IR) photodetectors is of interest for three-dimensional vision applications spanning consumer electronics, augmented reality, machine vision, and autonomous driving. Colloidal quantum dots (CQDs) are appealing toward this end: they unite IR-tunable absorption with ease of fabrication. To date, CQD photodetectors operating in the short-wave IR have failed to provide the combination of high responsivity, detectivity, and fast temporal response. To advance this field, large-diameter CQDs are needed that combine passivation with efficient charge transport. Here, we present an efficient ligand-exchange strategy tailored to large CQDs having a band gap of 0.8 eV. The new well-passivated stable colloidal quantum dots enable high-quality CQD photoactive layers with exceptional optoelectronic properties. As a result, short-wavelength IR photodetectors operating at 1,550 nm with a record external quantum efficiency, reasonable detectivity, and fast response time are demonstrated. Photodetectors operating in the short-wave IR range (SWIR) are needed for emerging three-dimensional vision applications. Solution-processed semiconductors offer tunable absorption into the SWIR and low-cost fabrication comparing to the epitaxially grown semiconductors. In this study, we present an efficient route to process large colloidal quantum dots with band gap of 0.8 eV into high-quality solids with exceptional optoelectronic properties. The fabricated SWIR photodiodes exhibit a record external quantum efficiency and reasonable detectivity at 1,550 nm as well as a fast response time.