Transparent and conductive titanium indium zinc oxide/Ag/titanium indium zinc oxide multilayer films deposited by radio frequency magnetron co-sputtering

doi:10.1016/j.tsf.2014.02.045

Thin Solid Films

Volume 558, 2 May 2014, Pages 31-36

https://doi.org/10.1016/j.tsf.2014.02.045 Get rights and content

Highlights

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We investigate the properties of TiInZnO/Ag/TiInZnO multilayer films.
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Transparent and conductive TiInZnO/Ag/TiInZnO multilayer films were obtained.
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The optimum film showed the sheet resistance of 7.7 Ω/□ and the transmittance of 92%.
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The multilayer films had good mechanical durability regarding external dynamic stress.

Abstract

Multilayer transparent films with lower electrical resistance than the widely used transparent conductive electrodes, were prepared at room temperature on flexible PES [poly(ether sulfone)] substrates using an RF-magnetron co-sputtering system. The multilayered films consisted of three layers, titanium indium zinc oxide (TIZO)/Ag/TIZO. The optical and electrical properties of the multilayered TIZO/Ag/TIZO structure were investigated in relation to the thickness of each layer. A transparent and conductive film with a sheet resistance of 7.7 Ω/□ and an average transmittance of 92% (normalized to the flexible PES substrate) at 550 nm, was obtained at thicknesses of PES/TIZO(100 nm)/Ag(10 nm)/TIZO(40 nm). The surface roughness (root mean square, RMS) values of the obtained multilayer films were below 1 nm. Overall, the properties of the film were comparable or superior to those of other multilayer films such as indium tin oxide (ITO)/Ag//ITO, indium zinc oxide (IZO)/Ag/IZO, and indium zinc tin oxide (IZTO)/Ag/IZTO. For this reason, the new TIZO/Ag/TIZO multilayer film may serve as a viable, high-efficiency alternative for electrode applications in flexible photovoltaic cells.

Introduction

Transparent, conductive electrode films, showing the particular characteristics of good conductivity and high transparency, are of considerable research interest because of their potential for use in optoelectronic applications, such as photovoltaic cells and flat panel displays [1], [2], [3], [4]. The most common transparent conductive electrode materials are indium tin oxide (ITO) and fluorine tin oxide (FTO). Indium oxide (In₂O₃)-based material has been doped with tin (Sn) to improve its electrical conductivity. On the other hand, FTO is well known to be thermally stable up to 650 °C, and thereby suitable for the thermal processes used in preparing amorphous silicon solar cells, or dye-sensitized solar cells (DSSCs) [5], [6], [7]. These kinds of materials currently play an important role as transparent electrodes for photovoltaic cells and flat panel displays. However, increasing technological demand for next-generation optoelectronic devices makes it necessary to investigate more advanced materials and structures with lower resistivity and higher transparency.

Recently, ITO/metal/ITO multilayers have gained much attention as promising anode materials for organic light-emitting diodes (OLEDs) because the dielectric/metal/dielectric multilayer system can suppress the reflection from the metal layer and obtain a selective transparency effect [8], [9], [10]. Lewis et al. [11] suggested that the electrical and mechanical properties of an ITO/Ag/ITO anode could be remarkably improved by placing a continuous silver (Ag) layer between the ITO layers. Kim et al. [12], [13] also reported that InZnO/Ag/InZnO and InZnSnO/Ag/InZnSnO electrodes could provide low sheet resistance and high transmittance, as well as superior flexibility in flexible OLEDs, due to the effect of the ductile Ag layer.

In our previous work [14], we reported a combinatorial investigation of titanium indium zinc oxide (TIZO) as a transparent conductive electrode film, specifically, for flexible solar cells and displays. Although it was deposited at room temperature, a high-quality amorphous TIZO film with a resistivity of 3.8 × 10^− 4 Ω cm and transmittance of 92% (normalized to the flexible PES substrate) at 550 nm, were obtained after reducing the amount of indium content used in conventional ITO and IZO films.

In this work, TIZO/Ag/TIZO multilayer films were prepared at room temperature on PES substrates using an RF-magnetron co-sputtering system. The optical and electrical properties of the multilayered structures were investigated according to the thickness of each layer. High-quality TIZO/Ag/TIZO multilayer films, with sheet resistance lower than conventional ITO or IZO films, were obtained. The characteristics of these TIZO/Ag/TIZO multilayers have not yet been reported.

Section snippets

Experimental details

The TIZO/Ag/TIZO multilayer films were prepared on PES [poly(ether sulfone)] substrates (i-Components Co.) using an RF-magnetron co-sputtering system. Fig. 1 shows a schematic diagram of the system, which consists of a vacuum chamber reactor (ULVAC MB07-4501) equipped with four 4-in. sputtering guns. A TiO₂ [99.99%, 4-in.] and a 10 wt.% Zn-doped In₂O₃ (IZO) [99.99%, 4-in.] target was used to deposit the TIZO film. Co-sputtering of the TIZO film was conducted at the RF power of 200 W (IZO) and 50 W

Results and discussion

Fig. 2 shows the sheet resistance values of the TIZO single-layer and the TIZO/Ag/TIZO multilayered films deposited on PES substrate, as a function of thickness of each layer. The 150 nm-thick TIZO single-layer film (without an inserted Ag interlayer) had a sheet resistance of 32.2 Ω/□. However, insertion of an Ag interlayer remarkably lead to reduced sheet resistance as shown in Fig. 2. It was shown that the sheet resistance of the TIZO/Ag/TIZO multilayers significantly decreased with an

Conclusion

This work focused on the sputtering deposition and analysis of TIZO/Ag/TIZO multilayer films prepared on flexible PES substrate by RF-magnetron co-sputtering using the TIZO film. This film has a smaller quantity of expensive indium than conventional ITO film. The electrical and optical properties of the new multilayer films were mainly dependent on the thickness of the inserted Ag layer. Although the TIZO/Ag/TIZO multilayer film was deposited at room temperature, the transparent and conductive

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Transparent and conductive titanium indium zinc oxide/Ag/titanium indium zinc oxide multilayer films deposited by radio frequency magnetron co-sputtering

Highlights

Abstract

Introduction

Section snippets

Experimental details

Results and discussion

Conclusion

Thin Solid Films

Sol. Energy Mater. Sol. Cells

Opt. Commun.

Thin Solid Films

Thin Solid Films

Thin Solid Films

Thin Solid Films

Surf. Coat. Technol.

Thin Solid Films

Thin Solid Films

C. R. Chim.

Sol. Energy Mater. Sol. Cells