Inverted Device Architecture for Enhanced Performance of Flexible Silicon Quantum Dot Light-Emitting Diode

Abstract

Here we report for the first time highly flexible quantum dot light-emitting diodes (QLEDs), in which a layer of red-emitting colloidal silicon quantum dots (SiQDs) works as the optically active component, by replacing a rigid glass substrate with a thin sheet of polyethylene terephthalate (PET). The enhanced optical performance for electroluminescence (EL) at room temperature in air is achieved by taking advantage of the inverted device structure. Our QLEDs do not exhibit parasitic EL emissions from the neighboring compositional layers or surface states of QDs over a wide range of driving voltages and do not exhibit a shift in the EL peak position as the operational voltage increases. Compared to the previous Si-QLEDs with a conventional device structure, our QLED has a longer device operational lifetime and a long-lived EQE value. The currently obtained brightness (∼5000 cd/m), the 3.1% external quantum efficiency (EQE), and a turn-on voltage as low as 3.5 V are sufficiently high to encourage further developments of Si-QLEDs.

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

“…As summarized in Figure 4b, it is obvious that the values of EQE were not diminishing greatly even after exposure to 80% humidity in air. Specifically, EQE values of the same devices after the exposure dropped a maximum 10% when compared to the value of the as- Blueshift of EL spectra with increasing device bias is still one of common problems observed for QLEDs prepared from colloidal inks of semiconductors [20]. For Si, a similar problem is reported in literature when the QLED has a conventional device structure.…”

“…The luminance reached a value as high as 1400 cd/m 2 at current density 0.0032 A/cm 2 . Blueshift of EL spectra with increasing device bias is still one of common problems observed for QLEDs prepared from colloidal inks of semiconductors [20]. For Si, a similar problem is reported in literature when the QLED has a conventional device structure.…”

“…Blueshift of EL peak with increasing driving voltage has been also reported for NIR-emitting Si-QLEDs [4,29]. It is reported that inversed device structures of QLEDs work for minimizing such unwanted spectral shift even at high driving voltage [20,30,31]. The inverted device structures reported usually consist of an organic-inorganic multilayer thin film architecture which is developed based on ITO/ZnO/QDs/CBP/Al structure.…”

“…A variety of metal oxides including zinc oxide (ZnO), nickel oxide (NiO), tungsten oxide (WO 3 ), and molybdenum oxide (MoO 3 ) have been used till now for carrier injection and transportation layers, resulting in the fabrication of a device that survives for a long operation time even in harsh environments [19]. More recently, we reported that inverted device structure allows the Si-QLED to demonstrate a stable optical performance even in high electronic fields, in addition to the long-life device stability [20]. We concluded that the device degradation originating from the intermixing effect could be evitable when the inverted structure is adopted, although the multilayer still contains organic HTL/HIL of 4,4 -bis(carbazole-9-yl)biphenyl (CBP) molecules.…”

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

“…Since the discovery of photoluminescence (PL) from porous silicon (Si) in 1991, many theoretical and experimental studies have focused on the development of a highly luminescent Si nanocrystal (ncSi) for applications in bioimaging, LEDs, and sensors [1][2][3][4][5][6][7][8][9]. Among these nanostructures, freestanding, highlystable, luminescent colloidal ncSihashas gained considerable attention due to its unique advantages, including high quantum yields (QYs) of PL.…”