Ultra-Violet Electroluminescence of ZnO Nanorods/MEH-PPV Heterojunctions by Optimizing Their Thickness and Using AZO as a Transparent Conductive Electrode

S Wageh,Su-Ling Zhao,Xiao-Yi Xie,Song Gao,Ahmed Al-Ghamdi

doi:10.3390/ma12182976

S Wageh, Su-Ling Zhao + Show 3 more

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https://doi.org/10.3390/ma12182976

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Abstract

In this paper, a series of ITO/ZnO/ZnO nanorods/MEH-PPV/Al were prepared with different thicknesses of MEH-PPV that were changed from 15, 10 to 7 nm. The electric field in the devices was analyzed. An increase in the electric field on ZnO made hole injection easy and the electrons tunnel fast through thinner MEH-PPV to ZnO. This made the carriers prefer to recombine inside the ZnO layer, and the emission of ZnO was predominant under direct current (DC) bias. Furthermore, another device was fabricated with the structure of AZO (Al-doped ZnO)/ZnO/ZnO nanorods/MEH-PPV/Al. Ultra-violet (UV) electroluminescence (EL) at 387 nm from ZnO band edge emission was realized under DC bias. The turn-on voltage of the devices having AZO as the electrode is lower than that of ITO, and the EL power is enhanced. This work also studies the effect of inserting LiF underneath the Al electrode and above the layer of MEH-PPV. The LiF film inserted caused an obvious decrease in turn-on voltage of the devices and a pronounced increase in the EL power. The mechanism of electroluminescence enhancement is also discussed.

Highlights

Oxide semiconductors with a wide direct band gap and exciton with large binding energy like zinc oxide have various optoelectronic applications
An insulator polymer Polymethylmethacrylate (PMMA) dissolved in chloroform with a concentration of 5 mg/mL was spin-coated onto the ZnO nanorods films with a rotation rate of 3000 rpm to fill the interspace between nanorods and insulate each other
Carriers will prefer to recombine inside the ZnO layer

Summary

Introduction

Oxide semiconductors with a wide direct band gap and exciton with large binding energy like zinc oxide have various optoelectronic applications. ZnO luminescence has been extensively studied due to its important optoelectronic applications It is used in laser operating devices and light emitting devices emitted in the ultraviolet region [1,2,3,4] ZnO is seen as a promising compound that can be used for light emission in ultra-violet (UV) region technology [5] in the generation. There is a problem in carrying out research on ZnO successfully This is the difficulty of fabricating p-type material of ZnO, apart from the fact that the wide band gap structures usually establish a feeble efficiency of p-type doping [6]. Several studies have been done to build light emitting devices using organic materials and tried to achieve the emission. A heterostructure consisting of an ZnO n-type semiconductor that works as an active layer and organic material that works as p-type compounds

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