Abstract
The performance of colloidal quantum dot light-emitting diodes (QD-LEDs) have been rapidly improved since metal oxide semiconductors were adopted for an electron transport layer (ETL). Among metal oxide semiconductors, zinc oxide (ZnO) has been the most generally employed for the ETL because of its excellent electron transport and injection properties. However, the ZnO ETL often yields charge imbalance in QD-LEDs, which results in undesirable device performance. Here, to address this issue, we introduce double metal oxide ETLs comprising ZnO and tin dioxide (SnO2) bilayer stacks. The employment of SnO2 for the second ETL significantly improves charge balance in the QD-LEDs by preventing spontaneous electron injection from the ZnO ETL and, as a result, we demonstrate 1.6 times higher luminescence efficiency in the QD-LEDs. This result suggests that the proposed double metal oxide ETLs can be a versatile platform for QD-based optoelectronic devices.
Highlights
For a few decades, there has been a growing interest in exploiting unique and superior optical properties of colloidal quantum dots (QDs) in various optoelectronic devices [1,2,3,4]
In our recent study [20], we have examined the use of SnO2 NPs for the electron transport layer (ETL) in QD-based light-emitting diodes (QD-light emitting diode (LED)), and found out SnO2 NPs have favorable interfacial properties with QDs that do not induce spontaneous electron injection; SnO2 NPs have
In order to take advantage of SnO2 NPs while maintaining an excellent electron transporting ability of the standard zinc oxide (ZnO)-based ETL, we propose a new ETL platform comprising the stack of ZnO and SnO2 NPs
Summary
There has been a growing interest in exploiting unique and superior optical properties of colloidal quantum dots (QDs) in various optoelectronic devices [1,2,3,4]. Low-cost solution processability and flexibility are appealing properties of QDs to enable next-generation displays. Based on these advantages, the various QDs comprised of II-VI [8,9], III-V [10,11,12], IV [13,14], perovskite [15,16], are actively developing for display application. The efficiency of QD-based light-emitting diodes (QD-LEDs) has been improved steadily over the past two decades, and one of the most important breakthroughs was made by employing a metal oxide semiconductor in the electron transport layer (ETL). As a result of intensive investigation, the ZnO ETL is considered as a standard platform for high-performance QD-LEDs, and the state-of-the-art QD-LEDs employ ZnO-based ETL [10,22]
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