Ultra‐Thin Infrared Optical Gain Medium and Optically‐Pumped Stimulated Emission in PbS Colloidal Quantum Dot LEDs

Abstract

Colloidal semiconductor quantum dots (QDs) can be considered a promising material platform for solution-processed laser diodes. However, due to some fundamental challenges, the realization of electrically pumped lasing based on QDs remains unresolved. Here, a binary blend of QDs and ZnO nanocrystals is employed, which serve as nano-sized scatterers to facilitate waveguide gain in ultra-thin films. By carefully engineering the electric field in these films, an infrared amplified spontaneous emission in a record thin colloidal gain medium is observed, with a thickness of 16 nm, at a wavelength of 1675 nm. Employing these binary blends as a gain medium, an optically pumped infrared stimulated emission in a full-stacked light-emitting diode (LED) device is demonstrated. The functional LED device, which comprises a single layer of graphene as an anode electrode, shows strong electroluminescence under electrical injection. This study suggests a promising device for realizing infrared QD-based laser diodes.

Colloidal Quantum Dot Infrared Lasers Featuring Sub‐Single‐Exciton Threshold and Very High Gain

“…[8,[10][11][12] The required high number of excitons within a CQD leads to an unfavorable, competitive-to-lasing process known as Auger recombination, where the exciton energy is transferred to a third carrier that subsequently undergoes non-radiative relaxation, [5,8,13] leading to optical gain lifetime, τ g , of tens of picoseconds in standard CQDs. [5,10,12,13] Room-temperature tunable infrared amplified spontaneous emission (ASE) and lasing have been recently demonstrated in PbS-, [10][11][12]14] and Ag 2 Se-based CQDs. [15] Particularly, PbS-based CQDs show ASE/lasing thresholds in the range of 500-2000 µJ cm −2 , [10,11,14] a gain lifetime of 40 ps, [10] and a limited gain coefficient of 120 cm −1 .…”

Metal Halide Perovskites toward Electrically Pumped Lasers

“…[ 50,246 ] Aiming at these challenges, there have been considerable advancements related to the exploration of optical gain phenomena and intense current density in LEDs. [ 65,73,246–249 ]…”

“…[50,246] Aiming at these challenges, there have been considerable advancements related to the exploration of optical gain phenomena and intense current density in LEDs. [65,73,[246][247][248][249] To explore the compatibility of optical microcavities with functional LEDs, Kim et al introduced DFB gratings (patterned on perovskite layer or ITO electrode) in a LED structure to demonstrate a peak EQE of 0.1% and a maximum current density of 2 A cm −2 under electrical pulse operation and the lasing with thresholds as low as 6 μJ cm −2 (Figure 15a,b). [246] Subsequently, Liang et al incorporated a bottom DBR under the ITO electrode of the red, green, and blue perovskite micro-LED array, forming a F-P resonant cavity with the metal electrode reflector.…”

Highly Monodisperse PbS Quantum Dots with Facet Engineering for High-Radiance Light-Emitting Diodes in the NIR-II Window

“…Light-emitting diodes (LEDs) in the second near-infrared window (NIR-II, 1000–1700 nm) have greatly promoted the development of optical communication, night vision, and biomedical diagnosis due to the special functionalities of the spectral region. − Traditional NIR-II LEDs based on InGaAs semiconductors and inorganic phosphors usually require trenchant processing technology such as vacuum deposition and high-temperature sintering (>1000 °C), which are huge roadblocks for low-cost and flexible implementations. − PbS quantum dots (QDs), on the other hand, not only have the advantages of NIR-II emission tunability, high quantum yield, multiple exciton generation, and high stability but also can be synthesized by low-temperature and solution-processed methods. − PbS QD light-emitting diodes (QLEDs) have a broad application prospect as one of the novel NIR-II light source technologies, , especially for commercial applications in emerging fields such as security authentication, optogenetics, and 3D imaging. However, NIR-II PbS QLEDs with high radiance are difficult to achieve due to the suboptimal PbS QD materials and device structure.…”

“…4−6 PbS quantum dots (QDs), on the other hand, not only have the advantages of NIR-II emission tunability, high quantum yield, multiple exciton generation, and high stability but also can be synthesized by low-temperature and solution-processed methods. 7−14 PbS QD light-emitting diodes (QLEDs) have a broad application prospect as one of the novel NIR-II light source technologies, 11,15 especially for commercial applications in emerging fields such as security authentication, optogenetics, and 3D imaging. However, NIR-II PbS QLEDs with high radiance are difficult to achieve due to the suboptimal PbS QD materials and device structure.…”