Full-Color Quantum Dot Light-Emitting Diodes Based on Microcavities

Abstract

Full-color display is a primary challenge for the commercialization of quantum dots (QDs). In this study, we utilize the spectral narrowing phenomenon of microcavities to fabricate the red, green and blue quantum dot light-emitting diodes (QLEDs) with a single QD layer. This work theoretically analyses the role of microcavities in adjusting the emitting color of QLEDs. By enhanced microcavity and properly chosen spacer thickness, the spectral selectivity shifts, realizing the full-color-tunability of QLEDs. The tunable experimental spectra of microcavity QLEDs are observed, in excellent agreement with our theoretical design. Benefiting from the spectral narrowing of microcavity and the narrow spectra of QDs, a high color purity with full width at half maximum (FWHM) of 18 to 25 nm is realized, leading to a color gamut ratio of 104.8% compared to National Television System Committee (NTSC) standard. The light extraction is also enhanced by constructive interference and the Purcell effect in the microcavity. Moreover, in the fabrication of red, green, and blue pixels, patterning the transparent cathode has better feasibility and lower damage relative to patterning the light-emitting layer.

High-performance top-emitting quantum dot light-emitting diodes by balancing electrical conductance and light outcoupling

“…In our device, there is wide-angle interference for the light generated inside the devices. 17,39 Interference arises within the cavity when the directly emitted light and reflected light from the bottom electrode with the same wavevector overlap, as shown in Fig. S6 (ESI †).…”

Microcavity Design Upping Light Extraction Efficiency over 50% in High‐Index Perovskite Light‐Emitting Diodes

“…Therefore, the reflection from the semitransparent electrode is very weak in the escape cone, and the effects of Equations () and () are limited. In other words, the wide‐angle interference described by Equation () is dominant in common bottom‐emission PeLEDs, [ 38,39 ] and we can call those PeLEDs the weak‐microcavity PeLED. [ 54,55 ] On the contrary, a strong‐microcavity PeLED can be formed if the semitransparent electrode is a thin metal film, such as silver (Ag) or aluminum (Al).…”

“…It should be noted that the maximum intensity for optimal efficiency is not in the normal direction because the solid angle (dΩ = sin θdθdφ) is small near the normal direction (θ ≈ 0). [ 39 ] It is worth noting that although non‐Lambertian emission may not be suitable for planar display, it can be potentially applied to augmented reality (AR) and virtual reality (VR) displays owing to the concentrated emission and the high efficiency.…”

“…[37] As shown in Figure 1c,d, the microcavity introduces wide-angle and multiple-beam interference. [38][39][40] The former is the interference between directly emitted and reflected waves with the same wave vector, while the latter describes that the light is reflected back and forth and superposed with itself. The Purcell effect describes the enhancement or inhibition of the spontaneous decay rate of an emitter in the device struc-ture compared to that in free space.…”

Randomly Disassembled Nanostructure for Wide Angle Light Extraction of Top‐Emitting Quantum Dot Light‐Emitting Diodes

“…On the other hand, the top-emitting QLEDs (TE-QLEDs) are usually free from the substrate mode due to the strong microcavity effect [13] and possess a pure color gamut, which is preferable for television displays. [14] However, as discussed in studies on TE-QLEDs, the topemitting structure usually suffers from a relatively poor viewing angle, which significantly varies from the general Lambertian viewing angle because of the excessively focused light extraction toward the normal direction. [15] In response to these issues, various methods have been utilized, including dielectric Bragg grating, [16,17] micro-lens arrays, [18,19] low-index grids, [20] photonic crystals, [21][22][23] and random structure.…”