Silicon Quantum Dots for Light-Emitting Diodes Extending to the NIR-II Window

Abstract

Biomedical applications rely on semiconductor quantum dots (QDs) exhibiting electroluminescence (EL) properties in the wavelength range between 1.0 and 1.7 μm (called the second near-infrared window, NIR-II). However, developing heavy-metal-free QDs remains a challenge. Herein, we report, for the first time, a colloidal silicon QD light-emitting diode (Si-QLED), which exhibits an EL spectrum with a peak at 1.0 μm along with a high external quantum efficiency (EQE) value of 4.84%, which is close to the record value among reported NIR-II EL devices. SiQDs as optically active layers are synthesized by thermal disproportionation of hydrogen silsesquioxane derived from triethoxysilane, followed by hydrofluoric etching. The photoluminescence quantum yield of SiQDs is improved up to 53% by thermal hydrosilylation of 1-decene, followed by careful extraction of highly emitting QDs using size exclusion chromatography. Si-QLEDs have an inverted device architecture with multilayers, leading to stable emission properties even at a high applied voltage. Furthermore, we demonstrate a spectral shape tuning of the EL spectra by taking advantage of a large Stokes shift between the optical absorption and emission, the property inherent to QDs of indirect band gap Si crystals.

Postproduction Approach to Enhance the External Quantum Efficiency for Red Light-Emitting Diodes Based on Silicon Nanocrystals

“…H-SiQDs liberated from the thermally disproportionated HSQ (i.e., white powder of SiQD/SiO x composite) were subjected to the thermal hydrosilylation of 1-decene, yielding De-SiQDs as shown in Figure 1 a. Only De-SiQDs with PLQY greater than 30% were fractionated by HPLC separation process as in the conventional method [ 20 ]. Figure 1 b shows a typical XRD pattern of the product after thermal hydrosilylation of 1-decene.…”

“…At present, QLEDs that meet the benchmark of 20% external quantum efficiency (EQE), which is comparable to the energy conversion efficiency of a mercury lamp, are limited to models that use indium phosphide QDs as an optically active layer [ 1 ]. In case of red-QLEDs, the possible QD alternatives are copper indium sulfide (CuInS 2 ) [ 2 ], ZnS-AgInS 2 (ZAIS) [ 3 ], Pb-free perovskite nanocrystals [ 4 ], and silicon (Si) [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ], but the EQE values reported for these QLEDs are still low, such as 7.8% for CuInS 2 [ 2 ], 2.2% for ZAIS [ 3 ], 0.3% for Pb-free perovskite [ 4 ], and 6.2% for Si [ 17 ].…”

Recent Progress in Controlled Nanostructure of Colloidal Nanocrystal Powders for Efficient Light Emission

“…The EL spectral peak position precisely tuned by diameter of SiQD. To date, the highest values of external quantum efficiency (EQE) at present were 4.8 %, 8.6 %, 3.36 %, 6.2 %, for the EL spectral peaking at 1000 nm (Watanabe et al, 2021), 853 nm (Cheng et al, 2011), 755 nm (Yamada et al, 2020), 720 nm (Ghosh et al, 2018), 700 nm (Liu X. et al, 2018), respectively. The EQEs of EL spectra peaking at the wavelength shorter than 700 nm are less than 1.2 % (Yamada et al, 2020).…”

Experimental Study of the Influence of CH4 and H2 on the Conformation, Chemical Composition, and Luminescence of Silicon Quantum Dots Inlaid in Silicon Carbide Thin Films Grown by Remote Plasma-Enhanced Chemical Vapor Deposition

“…Experimental and theoretical studies have shown that quantum confinement effects (QCEs) are largely responsible for the observed PL. − Luminescence from the nanostructured silicon has a vast number of applications. Therefore, systems conformed by silicon quantum dots (SiQDs) embedded in silicon-based matrixes have been of great interest for the scientific and technological community in recent years. − …”