Transparent InP Quantum Dot Light‐Emitting Diodes with ZrO₂ Electron Transport Layer and Indium Zinc Oxide Top Electrode

Abstract

Because of outstanding optical properties and non‐vacuum solution processability of colloidal quantum dot (QD) semiconductors, many researchers have developed various light emitting diodes (LEDs) using QD materials. Until now, the Cd‐based QD‐LEDs have shown excellent properties, but the eco‐friendly QD semiconductors have attracted many attentions due to the environmental regulation. And, since there are many issues about the reliability of conventional QD‐LEDs with organic charge transport layers, a stable charge transport layer in various conditions must be developed for this reason. This study proposes the organic/inorganic hybrid QD‐LEDs with Cd‐free InP QDs as light emitting layer and inorganic ZrO2 nanoparticles as electron transport layer. The QD‐LED with bottom emission structure shows the luminescence of 530 cd m−2 and the current efficiency of 1 cd/A. To realize the transparent QD‐LED display, the two‐step sputtering process of indium zinc oxide (IZO) top electrode is applied to the devices and this study could fabricate the transparent QD‐LED device with the transmittance of more than 74% for whole device array. And when the IZO top electrode with high work‐function is applied to top transparent anode, the device could maintain the current efficiency within the driving voltage range without well‐known roll‐off phenomenon in QD‐LED devices.

Flexible quantum dot light-emitting diodes for next-generation displays

“…114 In particular, flexible transparent displays enable novel curved display applications such as the smart car window, wearable smart watch, and public signage display. Until now, however, the EL performances of flexible transparent displays were significantly lower than those of their nontransparent counterparts, 115 mainly as a result of the constraints in transparent electrodes that require high conductivity, high transparency, and proper energy levels for effective charge injections simultaneously. 116 Table 2 summarizes the optical and electrical performances of previously reported transparent QLEDs including transparency, current efficiency, and device lifetime.…”

“…6h). 115 However, the transparent light-emitting devices still show low EL characteristics compared with the nontransparent counterparts because of imbalanced charge carriers within the devices. Moreover, the thick ETL and/or inorganic buffer layers increase the stiffness, thereby decreasing the flexibility of the QLEDs.…”

Transparent Conducting Electrodes for Quantum Dots Light Emitting Diodes

“…[40][41][42] To solve this problem, investigators have made several changes such as varying the deposition methods, using hard buffer layers, and employing low-damage sputtering in fabricating QDLEDs. [38][39] SnO 2 is also a wide-bandgap (3.62 eV) nonstoichiometric semiconductor with a low n-type resistivity (10 À 3 Ohm-cm) and high transparency (> 90 %) in the UV-visible region, and doping further reduces the nonstoichiometric resistivity to the range of 10 À 4 Ohm-cm. Therefore, SnO 2 has been doped with different chemical elements such as F, In, Sb, Fe, and many others to improve different physical properties.…”

Quantum Dot-Based Light Emitting Diodes (QDLEDs): New Progress

“…As mentioned, the best results in improving the stability of organic light emitting diodes are based on Cd QDs. InP quantum dots are replaced with Cd QDs in this study because of the environmental risks of cadmium [60]. In addition, the interface trap states are very effective on the performance of the device.…”