Inverted Quantum Dot Light Emitting Diodes using Polyethylenimine ethoxylated modified ZnO

Abstract

Colloidal quantum dots (QDs) are an emerging class of new materials due to their unique physical properties. In particular, colloidal QD based light emitting diodes (QDLEDs) have been extensively studied and developed for the next generation displays and solid-state lighting. Among a number of approaches to improve performance of the QDLEDs, the most practical one is optimization of charge transport and charge balance in the recombination region. Here, we suggest a polyethylenimine ethoxylated (PEIE) modified ZnO nanoparticles (NPs) as electron injection and transport layer for inverted structure red CdSe-ZnS based QDLED. The PEIE surface modifier, incorporated on the top of the ZnO NPs film, facilitates the enhancement of both electron injection into the CdSe-ZnS QD emissive layer by lowering the workfunction of ZnO from 3.58 eV to 2.87 eV and charge balance on the QD emitter. As a result, this device exhibits a low turn-on voltage of 2.0–2.5 V and has maximum luminance and current efficiency values of 8600 cd/m2 and current efficiency of 1.53 cd/A, respectively. The same scheme with ZnO NPs/PEIE layer has also been used to successfully fabricate green, blue, and white QDLEDs.

81‐2: High Performance Red Cadmium‐free Inverted Quantum Dot Light Emitting Diodes

“…Recently, several techniques such as Li:ZnO, AZO, double ETL (ZnO/Cs2CO3), PEIE, have been reported to improve charge carrier injection and efficiency of QLEDs. [8][9][10][11][12][13][14] In this work, we report cadmium-free (InP based QD) inverted red QLEDs with Mg doped ZnO nanoparticles as the ETL and stacked organic hole transport layers (HTL) for attaining high efficiency and excellent device performances. The red QLED containing optimized Mg (15%) doped ZnO layer exhibits maximum external quantum efficiency (EQE) of 4.46%.…”

P‐112: A Study on the Effect of Electrical Characteristics of HTL on Electrical Properties of QLED and its Efficiency

“…Among the factors influencing the luminous efficacy of QLED, the balance of electrons and holes injected into quantum dot layer has been investigated in various studies [1,2,3] and consequently non-radiative decays via Auger recombination was minimized to improve the efficacy [4]. In those studies, electron injection barrier such as a thin layer of insulating PMMA was inserted between electron transport layer (ETL) and the quantum dot light emission layer (EML) to reduce the injection of electrons into the EML.…”

P‐117: Inverted Quantum Dot Light‐Emitting Diodes with MgZnO Modified Electron Transport Layer

“…Among various methods, inserting a modified layer between ETL and QDs seems to be effective. A lot of materials, such as poly(methyl methacrylate) (PMMA) [4], polyethylenimine ethoxylated (PEIE) [14] and cesium carbonate (Cs 2 CO 3 ) [15], have been studied and utilized in QLEDs. However, most of these materials may limit the growth of current density due to their relatively insulated properties.…”