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Single layer graphene electrodes for quantum dot-light emitting diodes

This content has been downloaded from IOPscience. Please scroll down to see the full text. 2015 Nanotechnology 26 135201 (http://iopscience.iop.org/0957-4484/26/13/135201) View the table of contents for this issue, or go to the journal homepage for more

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Nanotechnology Nanotechnology 26 (2015) 135201 (6pp)

doi:10.1088/0957-4484/26/13/135201

Single layer graphene electrodes for quantum dot-light emitting diodes Long Yan1,2, Yu Zhang1,3, Xiaoyu Zhang1, Jia Zhao1, Yu Wang1, Tieqiang Zhang3, Yongheng Jiang3, Wenzhu Gao3, Jingzhi Yin1, Jun Zhao2,4 and William W Yu1,2,4 1

State Key Laboratory on Integrated Optoelectronics, and College of Electronic Science and Engineering, Jilin University, Changchun 130012, People’s Republic of China 2 College of Material Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, People’s Republic of China 3 State Key Laboratory of Superhard Materials, and College of Physics, Jilin University, Changchun 130012, People’s Republic of China 4 Department of Chemistry and Physics, Louisiana State University, Shreveport, LA 71115, USA E-mail: [email protected] and [email protected] Received 18 December 2014 Accepted for publication 26 January 2015 Published 9 March 2015 Abstract

Single layer graphene was employed as the electrode in quantum dot-light emitting diodes (QDLEDs) to replace indium tin oxide (ITO). The graphene layer demonstrated low surface roughness, good hole injection ability, and proper work function matching with the poly (3,4ethylenedioxythiophene):poly (styrenesulfonate) layer. Together with the hole transport layer and electron transport layer, the fabricated QD-LED showed good current efficiency and power efficiency, which were even higher than an ITO-based similar device under low current density. The result indicates that graphene can be used as anodes to replace ITO in QD-LEDs. Keywords: graphene electrode, ITO, CdSe/CdS/ZnS, quantum dots, light emitting diodes (Some figures may appear in colour only in the online journal) 1. Introduction

high photoluminescence (PL) quantum yield (QY), and narrow emission bandwidth. On account of these advantages, colloidal QDs have been widely employed in LED fabrication. Since the first demonstration of quantum dot-light emitting diodes (QD-LEDs) [20], various approaches have been proposed to improve the performance of these devices, such as the development of the QDs and transport materials, the optimization of carrier injection, and the design of novel device structures. All the efforts bring about the improvement of the device performance in terms of the brightness, the external quantum efficiency, and device stability. However, nearly all the studies employed indium tin oxide (ITO) as anode or cathode electrode. But the ITO raw materials are becoming increasingly expensive. The other disadvantages of ITO include high surface roughness due to its polycrystalline nature, instability of work function (WF) under different processing conditions and brittleness in flexible device application [21]. Therefore, it is desirable to develop lowcost, chemically stable and flexible new transparent electrodes

Graphene is a two-dimensional sheet of sp2-hybridized carbon atoms. It has plenty of advantages including high carrier mobility [1], great optical transparency [2, 3], outstanding flexibility [4, 5], good thermostability [6], and high mechanical strength [7]. The applications of graphene ranges from solar cells [8], light-emitting devices [9], field effect transistors [10], touch screens [11], ultrafast lasers [12], capacitors [13], to photodetectors [14]. In view of these applications, several methods have been proposed to obtain graphene films such as micromechanical exfoliation [15], epitaxial growth [2, 16], graphene oxide reduction [17], and chemical vapor deposition (CVD) [18]. Recently, graphene modification [19] and large-scale synthesis have made much progress making it convenient to fabricate optoelectronic devices with graphene. Colloidal quantum dots (QDs) have received considerable attention stemming from their ease of color tunability, 0957-4484/15/135201+06$33.00

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© 2015 IOP Publishing Ltd Printed in the UK

Nanotechnology 26 (2015) 135201

L Yan et al

such as graphene for the next generation optoelectronic devices. Recently, Klekachev et al for the first time employed graphene as the anode to fabricate QD-LEDs with a very simple structure without the demonstration of brightness and efficiency [22]. Based on their initial work, we introduced in this work the solution-processed poly[N,N-bis(4-butylphenyl)-N,N-bis(phenyl)benzidine] (poly-TPD) film as a hole transport layer (HTL), and the spin-coated ZnO nanoparticle film as an electron transport layer (ETL) into a graphenebased QD-LED in order to get a better device performance. As a result, the current efficiency (CE), power efficiency (PE) and brightness of the prepared device were much better improved. Further comparison to ITO anode-based control devices, the maximum CE and PE of the graphene based devices performed as good as the ones on ITO anodes. The CE and PE were even higher for graphene devices when working at low current density (

Single layer graphene electrodes for quantum dot-light emitting diodes.

Single layer graphene was employed as the electrode in quantum dot-light emitting diodes (QD-LEDs) to replace indium tin oxide (ITO). The graphene lay...
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