Highly efficient large-area quantum dot near-infrared light-emitting device for advanced non-invasive bioimaging

Advanced bioimaging requires a uniform and large-area near-infrared (NIR) light illumination source. Achieving uniform light typically involves the use of inorganic near-infrared light-emitting diodes (NIR-LEDs), such as AlGaAs or GaAs, which are often complemented by additional optical components like reflectors and diffusers. However, the use of such optical components imposes limitations on their applicability and flexibility. On the other hand, Quantum dot NIR LEDs (NIR-QLEDs) offer distinct advantages for bioimaging, as they directly emit light uniformly across their entire surface, without the need for any additional optical components. However, for state-of-the-art quantum dot-based NIR LEDs, the previous NIR-QLEDs have suffered from suboptimal charge transport and rapid degradation, limiting their radiance and EQE. This work addresses these limitations by demonstrating an industrial-friendly, all-solution processing technique for NIR-QLED device fabrication with significantly enhanced radiance and efficiency by utilizing copper (Cu) doped InP/ZnSe quantum dots (QDs). Cu-doping in InP/ZnSe QDs generates localized intra-gap states, enhancing carrier trapping and radiative recombination while suppressing non-radiative pathways, leading to unprecedented NIR peak emission at 924 nm and a narrow full-width at half maximum (FWHM) of 81 nm. These intra-gap states facilitate pure NIR emission, thereby substantially enhancing the device's efficiency. Based on the energy levels of the doped InP/ZnSe quantum dots (QDs), ZnMgO and WO₃ are employed as the electron transport layer (ETL) and hole transport layer (HTL), respectively. ZnMgO and WO₃ provide favorable conduction and valence band offsets, ensuring efficient carrier injection while suppressing leakage currents. The NIR-QLED exhibited an external quantum efficiency (EQE) of approximately 16 %. With a high current density of 250 × 10⁻³ A cm⁻², the radiance improved to 62 W sr⁻¹ m⁻². The all-solution processing technique employed in this work enabled the fabrication of a large emission area measuring 35 mm × 35 mm. Under illumination from this NIR-QLED, subcutaneous deep vein images were clearly observable. Consequently, this all-solution process not only simplifies the production process but also facilitates scalability, paving the robust route for the development of larger-area devices tailored for complex bioimaging applications.