Looking Inside a Working SiLED

Abstract

In this study, we investigate for the first time morphological and compositional changes of silicon quantum dot (SiQD) light-emitting diodes (SiLEDs) upon device operation. By means of advanced transmission electron microscopy (TEM) analysis including energy filtered TEM (EFTEM) and energy dispersive X-ray (EDX) spectroscopy, we observe drastic morphological changes and degradation for SiLEDs operated under high applied voltage ultimately leading to device failure. However, SiLEDs built from size-separated SiQDs operating under normal conditions show no morphological and compositional changes and the biexponential loss in electroluminescence seems to be correlated to chemical and physical degradation of the SiQDs. By contrast, we found that, for SiLEDs fabricated from polydisperse SiQDs, device degradation is more pronounced with three main modes of failure contributing to the reduced overall lifetime compared to those prepared from size-separated SiQDs. With this newfound knowledge, it is possible to devise ways to increase the lifetimes of SiLEDs.

Color tuning of indium phosphide quantum dots for cadmium‐free quantum dot light‐emitting devices with high efficiency and color saturation

“…The optimum seems to be yellow‐emitting QDs with the highest luminance and efficiency. For red‐emitting QDs, the worse size distribution most likely affects the layer morphology and therefore might increase parasitic currents and reduce efficiency . Additionally, the decreasing intensity of the photopic luminosity function used for the conversion from radiometric to photometric units like candela contributes to lower luminance values in the red range.…”

“…For red-emitting QDs, the worse size distribution most likely affects the layer morphology and therefore might increase parasitic currents and reduce efficiency. 38 Additionally, the decreasing intensity of the photopic luminosity function used for the conversion from radiometric to photometric units like candela contributes to lower luminance values in the red range. For green-emitting QDs, the high surface area of the small particles could be connected to a higher trap density and therefore reduce injection and recombination efficiency.…”

Water‐Dispersible Fluorescent Silicon Nanoparticles and their Optical Applications

“…Therefore, in future work, based on clear clarification of the sensing mechanism, novel high‐efficacy SiNP‐based sensors should be rationally designed for highly sensitive and specific detection and analysis in practical manners, to take advantage of the unique merits of SiNPs (e.g., strong fluorescence coupled with robust photostability, negligible toxicity and rich resource availability of silicon, etc.). On the other hand, although proof‐of‐concept LED devices have been constructed using fluorescent SiNPs, most of them generally possess low external quantum efficiency, which is hardly useful when comparing with well‐established fluorescent quantum dots (e.g., CdSe/ZnS QD)‐based LED devices. To address this critical issue, high‐quality SiNPs simultaneously featuring excellent monodispersity, good dispersibility, robust stability and high fluorescence (PLQY: 60–85%) are essentially required, and moreover, new device structures and corresponding fabrication techniques for SiNP‐based devices need to be established.…”

Influence of Meso and Nanoscale Structure on the Properties of Highly Efficient Small Molecule Solar Cells

“…The emitted photons are simultaneously collected by an EDX detector and enable chemical contrast in STEM-EDX measurements. [ 22,26,27 ] For the elemental quantifi cation in STEM-EDX, we chose carbon (present in both DCV5T-Me and C 60 ) and sulfur (present only in DCV5T-Me). Note that STEM-EDX shows the quantitative mapping of domain purity in real space and is thus complementary to reciprocal space methods such as R-SoXS.…”