Heterostructure from PbS Quantum Dot and Carbon Nanotube Inks for High-Efficiency Near-Infrared Light-Emitting Field-Effect Transistors

Light-emitting field-effect transistors (LEFETs) are emerging optoelectronic devices able to display simultaneously electrical switching as transistors and electroluminescence emission as light emitting diodes. Lead chalcogenide colloidal quantum dots (CQDs) allow achieving light emission in a very broad spectral range, covering the near-infrared (NIR) and the short-wavelength infrared (SWIR) regions, which cannot be reached with other solution-processable materials. Therefore, the use of lead chalcogenide CQDs as active layer in LEFETs opens the possibility for very narrow and switchable light sources in the NIR and SWIR range. The recently reported, first fully solid-state lead chalcogenide (PbS) CQD based LEFET shows an electroluminescence (EL) quantum efficiency of 1.3 × 10⁻⁵ at room temperature and of about 1% below 100 K. To overcome the limits of a previous report, an active material comprising two sequentially deposited layers is designed, the first of PbS CQDs displaying n-type transport and the second of polymer-wrapped semiconducting carbon nanotubes displaying p-type dominated transport. With this double layer system, LEFETs displaying a well-balanced ambipolar transport, charge carrier mobility of about 0.2 cm² V⁻¹ s⁻¹ for both electrons and holes, and EL external quantum efficiency reaching 1.2 × 10⁻⁴ at room temperature are obtained.