P‐108: Positive Aging Mechanisms for High‐efficiency Blue Quantum Dot Light‐emitting Diodes

Abstract

Voltage reduction (2.4 V at 2 mA/cm 2 ) and efficiency improvement (7-times) were demonstrated in blue QLEDs by positive aging process, which came from (1) improvement of carrier injection at ZnO/QD interface and/or carrier transport in QD layer, and (2) enhancement of PLQY of QD emissive layer. KeywordsQLED; blue emission; high efficiency; positive aging. P-108 / W.-C. Ding SID 2018 DIGEST • 1623

Shelf‐Stable Quantum‐Dot Light‐Emitting Diodes with High Operational Performance

“…Remarkably, a so-called positive ageing behaviour 12,[22][23][24] , i.e., improvements in device performance after short storage time of within several days, is generally observed for the state-of-the-art QLEDs, including the two red QLEDs with exceptionally long operational lifetime 13,20 . This phenomenon implies poor shelf stability of the QLEDs, albeit in a positive way.…”

Positive Aging Effect of ZnO Nanoparticles Induced by Surface Stabilization

“…In the first demonstration by Holloway et al., an interfacial reaction between ZnO and encapsulation resin was proposed as the cause for the observed 2.5-fold enhancement of luminance efficiency . Later, Lee et al also observed that the aging process can simultaneously improve the charge balance and photoluminescence quantum efficiency (PLQE) of the CdS QD emission layer . More recently, the enhancement of electron injection was further linked with the increased number of oxygen vacancies in ZnO, and the increased PLQE of emitters was attributed to the oxidation reaction between the ZnO layer and the top cathode .…”

“…An increased rate of electron transport upon aging is generally observed in quantum-dot photodiodes comprising ZnO NPs. − Here we first study the evolution of the transport mechanism during aging. Electron-only devices (ITO/ZnO/Al with encapsulation) are prepared for the study.…”

“…6 Later, Lee et al also observed that the aging process can simultaneously improve the charge balance and photoluminescence quantum efficiency (PLQE) of the CdS QD emission layer. 7 More recently, the enhancement of electron injection was further linked with the increased number of oxygen vacancies in ZnO, and the increased PLQE of emitters was attributed to the oxidation reaction between the ZnO layer and the top cathode. 8 According to the reports mentioned above, (i) the aging process increases the electron current in the photoactive layer, whereas the contribution from electron mobility, concentration, and energy-level alignment has not been identified; (ii) the aging process reduces the nonradiative recombination in the adjacent photoactive layer, but the underlying mechanism related to ZnO remains unclear; and (iii) besides the possible impact from deep-level defects in ZnO, such as oxygen vacancies, the role of nanoparticle surface chemistry should also be considered.…”

65‐3: Green Top‐emission Quantum Dot Light‐emitting Diodes (TE‐QLED) with Normal and Inverted Structure

“…Typically, the commercial product is utilizing of top-emission device because of aperture ratio issue. In general, aperture ratio of top emission is better than bottom-emission [12][13][14][15][16][17].…”