Optimization of Nb2O5/Ag/Nb2O5 multilayers as transparent composite electrode on flexible substrate with high figure of merit

Abstract

Different multilayer structures of Nb2O5/Ag/Nb2O5 have been deposited onto flexible substrates by sputtering at room temperature to develop an indium free transparent composite electrode. The effect of Ag thickness on the electrical and optical properties of the multilayer stack has been studied in accordance with the Ag morphology. The critical thickness of Ag to form a continuous conducting layer is found to be 9.5 nm. A new conduction mechanism has been proposed to describe the conduction before and after the critical thickness. The effective Hall resistivity of the optimized films is as low as 6.44 × 10−5 Ω-cm with a carrier concentration and mobility of 7.4 × 1021 cm−3 and 13.1 cm2 /V-s, respectively, at the critical Ag layer thickness. The multilayer stack has been optimized to obtain a sheet resistance of 7.2 Ω/sq and an average optical transmittance of 86% at 550 nm without any substrate heating or post-annealing process. The Haacke figure of merit (FOM) has been calculated for the films, and the multilayer with a 9.5 nm thick Ag layer has the highest FOM at 31.5 × 10-3 Ω−1, which is one of the highest FOM values reported for TCE deposited at room temperature on a flexible substrate.

A Method for Efficient Transmittance Spectrum Prediction of Transparent Composite Electrodes

“…[1][2][3][4] However, ITO contains the rare-earth element indium, and the extensive use of ITO drives researchers to develop low cost and sustainable replacement for ITO electrodes. [1][2][3][4] In recent years, transparent composite electrodes (TCEs) attract much interest because of their competitive electrical and optical properties. 4,5 TCEs have a trilayer thin-film structure, in which a metal layer is embedded between two transparent metal oxide (TMO) layers.…”

Highly Transparent and Low-Resistance Indium-Free ZnO/Ag/ZnO Multilayer Electrodes for Organic Photovoltaic Devices

“…So, Ag is commonly used as the middle layer in D/M/D multilayers (i.e., D/Ag/D). Numerous D/ Ag/D multilayers with different oxides have been investigated, including SnO 2 /Ag/SnO 2 , 8 Nb 2 O 5 /Ag/ Nb 2 O 5 , 9 TiInZnO/Ag/TiInZnO, 10 MoO 3 /Ag/MoO 3 , 11 WO 3 /Ag/WO 3 , 12 Al-doped ZnO(AZO)/Ag/AZO, 13 Al 2 O 3 /Ag/Al 2 O 3 , 14 ZrON/Ag/ZrON, 15 ZnSnO/Ag/ ZnSnO, 16 and TiO 2 /Ag/TiO 2 . 17,18 In particular, ZnO/ Ag/ZnO multilayers have been extensively studied by many researchers, [19][20][21][22][23][24] because ZnO is nontoxic, 25 cheap, 26 and abundant in nature; 27 For example, Sahu et al 20 investigated the optical and electrical properties of ZnO/Ag/ZnO multilayer electrodes as functions of the ZnO and Ag thicknesses, reporting that the optimum thickness of Ag thin films was 6 nm for high optical trans-(Received November 18, 2014; accepted April 23, 2015) mittance and good electrical conductivity, e.g., sheet resistance as low as 3 X/sq and transmittance of 90% at 580 nm.…”

High quality transparent TiO2/Ag/TiO2 composite electrode films deposited on flexible substrate at room temperature by sputtering

“…The difference at 500-600 nm wavelength region is due to light scattering at the TiO 2 /Ag interface in Ag isolated islands for Ag thickness below 8 nm and absorption of light due to interband electronic transitions from the 3d to unoccupied levels in the 4s band above Fermi level. 8,9 However, below this thickness, the transmittance decreases because the silver islands are discontinuous. In discontinuous Ag films, a size-dependent variation in the dielectric function is known to exist due to limitation of the mean free path of the conduction electrons.…”

“…), Nb 2 O 5 , TiO 2 , graphene, and carbon nanotube (CNT) sheets have been recently studied as potential alternatives to a-ITO electrodes on flexible substrates. [5][6][7][8][9] Recently, insertions of a very thin metal layer sandwiched between the two TCO layers have been studied to develop a transparent composite electrode (TCE) with the desired electrical conductivity. [9][10][11][12] Although metals have high reflectivity, very thin films (<15 nm) show moderate transmittance in the visible region and the top dielectric layer helps to obtain a higher transparent effect by diminishing the reflection from the metal layer.…”

“…These oxide/metal/oxide (OMO) multilayers are more efficient than a single-layer TCO film. [7][8][9][10][11][12][13] Titanium dioxide (TiO 2 ) is a potential semiconductor material with wide band gap (∼3 eV) and good adhesion to the glass and plastic substrates. 14,15 It has many excellent physical properties such as a high dielectric constant and a strong mechanical and chemical stability.…”