Impact of Anchoring Monolayers on the Enhancement of Radiative Recombination in Light-Emitting Diodes Based on Silicon Nanocrystals

Abstract

In the current paper, we provide direct evidence of a controlled structure of silicon nanocrystals (SiNCs). The photoluminescence quantum yields (PLQYs) are considerably enhanced by ligand exchange between the hydrogen atoms and hydrocarbon chains. To systematically study this phenomenon, we prepared SiNCs by thermal disproportionation of amorphous hydrogen silsesquioxane that was derived from triethoxysilane, which was followed by hydrofluoric etching and hydrosilylation of 1-alkenes. The estimated PLQY was 56% at maximum. The near-infrared (NIR) PL spectra of the specimens can be tuned by accurately controlling their diameters to engineer the fundamental gap. Through a combination of X-ray diffraction, Raman spectroscopy, and scanning transmission electron microscopy, we elucidated that the alkyl monolayers provide an anchor that prevents the lattice distortion of the diamond cubic lattice of Si, thus inhibiting the creation of nonradiative channels. This anchoring effect is responsible for the high PLQYs. The emissions were sufficiently strong for the fabrication of NIR light-emitting diodes that operate in the first biological window (650–900 nm) where the light absorption of water and the tissues including hemoglobin is minimal.

Influence of Oxidation on Temperature-Dependent Photoluminescence Properties of Hydrogen-Terminated Silicon Nanocrystals

“…Samples of ncSi-H were prepared by thermal disproportionationof amorphous hydrogen silsesquioxane at high temperature, as reported in our previous paper [3,10,32]. In a typical synthesis, 5 mL of TES (45 mmol) was added to a round-bottom flask equipped with a magnetic stir bar and stirred in Ar atmosphere using standard Schlenk techniques.…”

“…Among these nanostructures, freestanding, highlystable, luminescent colloidal ncSihashas gained considerable attention due to its unique advantages, including high quantum yields (QYs) of PL. In the past decade, considerable progress has been made toward realizing highly luminescent freestanding ncSi [10][11][12][13][14]. In the last two decades, freestanding hydrogen terminated ncSi (ncSi-H) with 1-2% PL QYs has been widely studied because Si-H bonds are promising to achieve various functionalizations with organics.…”

Nano-Bio Interaction between Blood Plasma Proteins and Water-Soluble Silicon Quantum Dots with Enabled Cellular Uptake and Minimal Cytotoxicity

“…Next, the QDs were terminated with decane monolayers via thermal hydrosilylation of 1-decene to yield SiQD-De ( Figure S1b, Supporting Information ). Termination of SiQDs with alkyl monolayers drastically enhanced PLQYs [ 40 , 41 , 42 ]. The absolute values of PLQY measured by a standardized integrating sphere method were 40–45% in this work.…”

All-Inorganic Red-Light Emitting Diodes Based on Silicon Quantum Dots

“…We observed the enhanced photoluminescence quantum yields (PL QYs) from 0.2% (for hydrogen-termination) to 18% (for decane-termination) as a result of preventing the formation of nonradiative recombination channels in the surface of the QDs [22]. We call this role of the alkyl monolayer on enhanced PL QY the "anchor effect" [23]. XRD spectra of the as-prepared Si QDs are shown in Figure 1a…”