We demonstrate highly efficient electroluminescence from silicon nanocrystals (SiNCs). In an optimized nanocrystal-organic light-emitting device, peak external quantum efficiencies of up to 8.6% can be realized with emission originating solely from the SiNCs. The high efficiencies reported here demonstrate for the first time that with an appropriate choice of device architecture it is possible to achieve highly efficient electroluminescence from nanocrystals of an indirect band gap semiconductor.

We report on the quantum yield, photoluminescence (PL) lifetime, and ensemble photoluminescent stability of highly monodisperse plasma-synthesized silicon nanocrystals (SiNCs) prepared though density-gradient ultracentrifugation in mixed organic solvents. Improved size uniformity leads to a reduction in PL line width and the emergence of entropic order in dry nanocrystal films. We find excellent agreement with the anticipated trends of quantum confinement in nanocrystalline silicon, with a solution quantum yield that is independent of nanocrystal size for the larger fractions but decreases dramatically with size for the smaller fractions. We also find a significant PL enhancement in films assembled from the fractions, and we use a combination of measurement, simulation, and modeling to link this "brightening" to a temporally enhanced quantum yield arising from SiNC interactions in ordered ensembles of monodisperse nanocrystals. Using an appropriate excitation scheme, we exploit this enhancement to achieve photostable emission.

We demonstrate hybrid inorganic-organic light-emitting devices with peak electroluminescence (EL) at a wavelength of 868 nm using silicon nanocrystals (SiNCs). An external quantum efficiency of 0.6% is realized in the forward-emitted direction, with emission originating primarily from the SiNCs. Microscopic characterization indicates that complete coverage of the SiNCs on the conjugated polymer hole-transporting layer is required to observe efficient EL.

The oxidation of freestanding silicon nanocrystals (Si-NCs) passivated with Si-H bonds has been investigated for a wide range of oxidation times (from a few minutes to several months) by means of electron spin resonance (ESR) of dangling bonds (DBs) naturally incorporated at the interface between the NCs core and the developing oxide shell. These measurements are complemented with surface chemistry analysis from Fourier-transform infrared spectroscopy. Two surface phenomena with initiation time thresholds of 15 minutes and 30 hours are inferred from the dependence of ESR spectra on oxidation time. The first initiates before oxidation of surface Si-Si bonds and destruction of the NCs hydrogen termination takes place (induction period), and results in a decrease of the DBs density and a localization of the DBs orbital at the central Si atom. Within the Cabrera-Mott oxidation mechanism, we associate this process with the formation of intermediate interfacial configurations, resulting from surface adsorption of water and oxygen molecules. The second surface phenomenon leads to a steep increase of the defects density and correlates with the formation of surface Si-O-Si bridges, lending experimental support to theoretically proposed mechanisms for interfacial defect formation involving the emission of Si interstitials at the interface between crystalline Si and the growing oxide.

Plasma‐synthesized silicon nanocrystals with alkene ligands have shown the potential to exhibit high‐efficiency photoluminescence, but results reported in the literature have been inconsistent. Here, for the first time, the role of the immediate post‐synthesis “afterglow plasma” environment is explored. The significant impact of gas injection into the afterglow plasma on the photoluminescence efficiency of silicon nanocrystals is reprorted. Depending on the afterglow conditions, photoluminescence quantum yields of silicon nanocrystals synthesized under otherwise identical conditions can vary by a factor of almost five. It is demonstrated that achieving a fast quenching of the particle temperature and a high flux of atomic hydrogen to the nanocrystal surface are essential for a high photoluminescence quantum yield of the produced silicon nanocrystals.