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

In the current paper, we provide direct evidence of a controlled structure of silicon nanocrystals (SiNCs). The photo-luminescence 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.