Fabrication of high-quality flexible transparent conductive thin films with a Nb2O5/AgNWs/Nb2O5 sandwich structure

Different sandwich structures of flexible transparent conductive thin film (TCFs) composed of Nb₂O₅ layers and Ag nanowires (AgNWs) have been prepared onto flexible polyethylene terephthalate (PET) substrate at room temperature to develop an indium-free TCF. The AgNWs are synthesized by a modified polyol method and inserted into the Nb₂O₅ layers that are prepared by radio frequency magnetron sputtering. The optical and electrical properties can be modified by changing the number of spin-coating cycle of AgNW suspension. At optimized condition, we achieve a flexible Nb₂O₅/AgNWs/Nb₂O₅ sandwich thin film with a low sheet resistance of 9.61 Ω/square and a high optical transmittance of 84.3%. Meanwhile, the resistance remains nearly constant after 30 tape tests, suggesting a strong adhesion to the PET substrate. The sandwich thin films show high long-term stability to oxidation, humid heat, and chemicals compared with that of AgNW networks, which can be attributed to the effective covering of Nb₂O₅ layer on the AgNWs. In addition, the Nb₂O₅/AgNWs/Nb₂O₅ sandwich thin films show good stability after repeated bending. This Nb₂O₅/AgNWs/Nb₂O₅ sandwich thin film can therefore serve as a high-performance transparent conductive electrode for numerous flexible electronic devices.     

High-performance indium-free flexible transparent ATO/Au/ATO tri-layer films by magnetron sputtering

Due to the scarcity of indium (In) in the earth and its potential harm to individuals, the development of In-free transparent conductive film is considered crucial. In this work, In-free SnO₂:Sb/Au/SnO₂:Sb (ATO/Au/ATO, SAS) tri-layer films with high transparency and conductivity were successfully prepared on polycarbonate (PC) substrates by RF and DC magnetron sputtering at room temperature. The influence of the Au layer thickness on microstructure, electrical and optical performances was systematically studied after fixing the ATO thickness to 50 nm. It was indicated by X-ray diffraction patterns that ATO is amorphous and Au is oriented along (111). The trend of increasing and then decreasing light transmission with Au layer thickness was observed in both experimental and simulation results. The improved figure of merit (FoM, 1.89 × 10^?2 Ω^?1) was achieved in SAS tri-layer film, the resistivity and average transmittance of which was lowered to 7.50 × 10^?5 Ω cm and 81.4%, respectively, when Au layer thickness is 11 nm. Moreover, the mechanism of the variation of optical and electrical properties at different Au layer thickness was proposed. Particularly, the SAS tri-layer films also exhibit superior flexibility, durability and adhesion. These results demonstrate SAS tri-layer films are promising alternative to ITO in flexible electronics applications.     

Lightwave irradiation-assisted low-temperature solution synthesis of indium-tin-oxide transparent conductive films

Transparent conductive oxide (TCO) films have important applications in many areas. Unfortunately, TCOs are usually fabricated using vacuum and high-temperature methods, preventing them from applications in low-cost flexible devices. In this paper, facile low-temperature sol-gel method is described that can be used to fabricate high-quality TCO films. This study uses lightwave (LW) irradiation (at ～280 °C) with indium-tin-oxide (ITO) as a typical example. Both structure and key properties of ITO films are investigated for different LW irradiation conditions. ITO can be formed via LW irradiation after a period as short as 5 min. Furthermore, it is found that LW irradiation can promote the formation of M ? O framework, effectively remove Cl impurities, and facilitate the elimination of hydroxyl oxygen defects - even at temperatures as low as ～280 °C. The optimal ITO films show excellent electronic properties, including low sheet-resistance (14.5 Ω·sq^?1) and high conductivity (1.7 × 10³ S cm^?1). Moreover, ITO films also show high transmittance (above 87%). Overall, our ITO films have a figure of merit (FOM) of 1.72 × 10^?2 Ω^?1, which is comparable to (or higher than) those of previous ITO films that were produced using conventional vacuum and high-temperature methods. Our LW irradiation method provides facile and effective approach to produce high-performance TCO films at remarkably low cost. This means these films could be used in affordable flexible large-area devices.     

ZnMgBeO/Ag/ZnMgBeO transparent multilayer films with UV energy bandgap and very low resistance

The ZnMgBeO/Ag/ZnMgBeO multilayer structures were sputter grown and their electrical and optical properties have been investigated in detail. Results indicated that the ZnMgBeO(30 nm)/Ag(10 nm)/ZnMgBeO(30 nm) optimum structure shows energy bandgap of ~4.5 eV, electrical resistivity of ~6.5×10⁻⁵ Ωcm, and optical transmittance of 78–90% over the visible wavelength range and 74–90% over 300–400 nm range, representing a significant improvement over the previously reported transparent conducting films. High resistivity (~0.12 MΩcm) of the ZnMgBeO layer did not critically affect the conductivity of the multilayer, because the Ag films act as the conducting path. It was also observed that the properties were substantially deteriorated at the Ag thickness of 5 nm, as the Ag film is only partly continuous, resulting in very rough interfaces and surfaces.     

High performance of carbon nanotubes/silver nanowires-PET hybrid flexible transparent conductive films via facile pressing-transfer technique

To obtain low sheet resistance, high optical transmittance, small open spaces in conductive networks, and enhanced adhesion of flexible transparent conductive films, a carbon nanotube (CNT)/silver nanowire (AgNW)-PET hybrid film was fabricated by mechanical pressing-transfer process at room temperature. The morphology and structure were characterized by scanning electron microscope (SEM) and atomic force microscope (AFM), the optical transmittance and sheet resistance were tested by ultraviolet-visible spectroscopy (UV-vis) spectrophotometer and four-point probe technique, and the adhesion was also measured by 3M sticky tape. The results indicate that in this hybrid nanostructure, AgNWs form the main conductive networks and CNTs as assistant conductive networks are filled in the open spaces of AgNWs networks. The sheet resistance of the hybrid films can reach approximately 20.9 to 53.9 Ω/□ with the optical transmittance of approximately 84% to 91%. The second mechanical pressing step can greatly reduce the surface roughness of the hybrid film and enhance the adhesion force between CNTs, AgNWs, and PET substrate. This process is hopeful for large-scale production of high-end flexible transparent conductive films.     

Manganese-doped transparent conductive magnetic indium oxide films integrated on flexible mica substrates with high mechanical durability

Recent advances in flexible electronic devices have stimulated demands for the fabrication of multifunctional materials on highly flexible substrates. However, flexible diluted magnetic semiconductor films have been inadequately reported thus far. In this study, I grew polycrystalline manganese (Mn)-doped indium oxide (In₂O₃) films on flexible mica substrates at three deposition temperatures (T_d) using the pulsed laser deposition method. All the investigated Mn-doped In₂O₃ films exhibited high optical transparency, high electrical conductivity, room-temperature ferromagnetism, and excellent mechanical durability. The present experimental results demonstrate that T_d considerably influences the optical, electrical, and magnetic properties as well as the mechanical durability of the flexible Mn-doped In₂O₃ films. Based on the robustness of inorganic mica at high deposition temperatures, this detailed investigation provides a strategy for fabricating flexible diluted magnetic semiconductor films, the properties of which could be carefully optimized by widely varying the T_d.     

Spray-grown highly oriented antimony-doped tin dioxide transparent conducting films

Undoped and Sb-doped tin dioxide films of varying thickness with a remarkable crystallographic orientation in the [200] direction were grown by spray-pyrolysis from tin(II) chloride solutions. Films grown on silica-coated glass substrates were completely crystalline and showed a higher degree of orientation with respect to films that were grown on uncoated glass. The presence of the silica barrier was seen to have increased the degree of orientation and to have enhanced the resulting electrical properties. Transmission electron microscopy revealed that the silica layer may have played the crucial role of a nucleation layer. Moreover, the developed microstructures were correlated with the optical and electrical behaviour of the films. Dense conducting films with thicknesses between 280–450 nm and visible transmittances of 80-70 % showed resistivities of about 10⁻³ Ωcm.     

Highly flexible and thermal conductive films of graphene/poly(naphthylamine) and applications in thermal management of LED devices

In 5G era, integration and miniaturization of electronic components lead to increasing challenges in thermal management. Materials with high thermal conductivity and flexibility are strongly desired for dissipating heat locally generated in such devices. Due to its extraordinary thermal conducting performance, graphene has been exhibiting great potential in thermal management. In this work, composite films based on graphene oxide and poly-naphthylamine (gGO/PNA) with enhanced thermal conducting performance have been achieved by employing poly (naphthylamine) (PNA) as repairing additives to restore topological defects of graphene oxide (GO). Specifically, gGO/PNA films are prepared with a facile operation of vacuum filtration followed by an elevated temperature treatment. The optimal thermal conductivity (κ) of gGO/PNA reaches to 1016.03 W m⁻¹ K⁻¹, 31.3% enhancement over that of the pristine graphene one. The thermal conducting performance test demonstrates the film an efficient heat-dissipation ability from a heat-generating LED bulb. Furthermore, the film exhibits excellent flexibility, making it survival from a 1000-cycle bending test. This finding may promote the development of heat-spreading materials and their applications in thermal management of highly integrated electronics.     

Ga and Ti co-doped In2O3 films for flexible amorphous transparent conducting oxides

We designed Ga and Ti co-doped In₂O₃ (IGTO) films to use as a flexible and transparent amorphous conducting oxide electrode in thin film heaters (TFHs) and flexible touch screen panels (FTSPs) for automobiles. The properties of the IGTO electrodes deposited on cyclic olefin copolymer (COP) at room temperature were investigated as a function of the O₂/(Ar + O₂) flow ratio, to confirm the best sputtering condition for transparent and flexible electrode. Depending on the oxygen flow ratio, the IGTO/COP electrodes showed sheet resistance of (39.3 – 1.57) × 10⁴ Ohm/sq, an average transmittance of (84.90 – 87.12) % at visible wavelength area, and a surface roughness of (0.95 – 3.23) nm. In addition, IGTO/COP samples exhibited good mechanical flexibility with critical bending radius of 3 mm, which is enough to be used as FTSPs. From the previously mentioned results, we found the amorphous IGTO/COP to be a promising flexible and transparent electrode for curved TFHs and FTSPs. The flexible IGTO/COP TFHs demonstrated a saturated temperature of 78.6 °C when applied with low operating direct current (DC) of 8 V, due to its low sheet resistance. In addition, the IGTO/COP FTSPs showed very stable touch sensitivity, even at a bent state. We found that the optimized IGTO/COP is a promising flexible and transparent electrode for next-generation automobiles.     

A leaf-like structured ITO conductive transparent thin film from visible to near-infrared region with enhanced stability

ITO thin films as the optical and electrical windows to transform photons and charges have been applied in many areas. Here, a leaf-like structured particle is composed of small particles growing along three different orientations leading to low thermal stress accompanied by well transmittance (85%) in a wide wavelength range from visible to near-infrared region and a narrowed band gap 3.07 eV. The evolution of structure and electronic performance was studied to obtain the low resistivity (12 μΩ m) and enhanced stability of the film (1000 °C). The leaf-like structure can be maintained under 600 ℃ and the electrical properties can be modified in He and N₂ atmosphere, owing to the reduced defects, increased concentration of Sn and carrier mobility. Although the structure has changed after being annealed at 1000 °C in N₂, the thin film performs excellent electrical properties (?3.44 × 10²⁰ cm^?3 and 28 cm² V^?1 s^?1).     

Highly conducting and transparent antimony doped tin oxide thin films: the role of sputtering power density

Sb doped SnO₂ thin films were deposited on quartz substrates by magnetron sputtering at 600 °C and the effects of sputtering power density on the preferential orientation, structural, surface morphological, optical and electrical properties had been studied. The XRD analyses confirm the formation of cassiterite tetragonal structure and the presence of preferential orientation in (2 1 1) direction for tin oxygen thin films. The dislocation density analyses reveal that the generated defects can be suppressed by the appropriate sputtering power density in the SnO₂ lattice. The studies of surface morphologies show that grain sizes and surface roughness are remarkably affected by the sputtering power density. The resistivity of Sb doped SnO₂ thin films gradually decreases as increasing the sputtering power density, reaches a minimum value of 8.23×10⁻⁴ Ω cm at 7.65/cm² and starts increasing thereafter. The possible mechanisms for the change in resistivity are proposed. The average transmittances are more than 83% in the visible region (380–780 nm) for all the thin films, the optical band gaps are above 4.1 eV. And the mechanisms of the variation of optical properties at different sputtering power densities are addressed.     

柔性纳米银线导电薄膜的制备及其性能研究

通过2步加入多元醇热还原法制备出了高长径比的纳米银线,并在柔性基材上制备兼具透光性和导电性的薄膜;对薄膜与基材的粘接性能进行了改善。采用X-射线衍射(XRD)、扫描电子显微镜(SEM)、场发射透射电子显微镜(FETEM)对纳米银线的相结构及形貌进行了分析及表征。薄膜的透光率和导电性分别通过紫外-可见分光光度计和四探针进行了研究。制备的纳米银线的直径约为50 nm,长径比为200~300。研究了银线浓度以及用量对真空抽滤转移法制备薄膜的透光率及导电性的影响,发现当银纳米线的浓度为0.025mg/mL,薄膜的透光率为71.0%时,方块电阻为65.5Ω/sq。所制备的薄膜在基材上的粘接性通过旋涂一层聚偏氟乙烯(PVDF),并经热处理后,粘接性和导电性(方阻为18.0Ω/sq)都有所提高。     

淀粉基底银纳米线柔性透明导电薄膜的合成及光电性能

以马铃薯淀粉为原料,合成可反复弯曲折叠的柔性透明基底膜,通过多元醇法制备导电银纳米线(Ag NW),用旋涂法将Ag NW均匀覆盖于淀粉基底膜表面,两者通过分子间作用力相结合,制得系列Ag NW沉积密度不同的复合导电薄膜材料。对产品形貌、结构及稳定性进行了分析,并探索了不同AgNW沉积密度对复合导电薄膜材料光电性能的影响规律。结果表明,获取的柔性基底膜具有92%透光率、3.92 nm粗糙度、29.01 MPa拉伸应力;导电银纳米线直径约60 nm,长度20～30μm。当Ag NW沉积密度超过300 mg/m2时,方块电阻(Rs)低于22.6?/sq,透光率低于65%,光电优值(FOM)高于35,是氧化铟锡(ITO)导电膜的良好替代材料。将复合膜反复弯曲折叠Rs变化量低于5%,TGA测试发现,淀粉基底膜及复合膜热分解温度高于250℃,有利于对其进行进一步高温导电处理;稳定性测试结果表明,复合膜放置于空气中随时间延长Rs略微增大。     

High-performance flexible dielectric tunable BTS thin films prepared on copper foils

High-performance flexible dielectric tunable BaSn_0.15Ti_0.85O₃ thin films are prepared by barrier layer of Sb doped SnO₂ on the copper foils. Dielectric measurements indicate that the flexible thin films exhibit a low dielectric loss of below 0.007, a medium dielectric constant of ∼378, and the superior tunable dielectric properties at room temperature. Calculations of tunability and figure of merit (FOM) display a maximum value of 66.5% at 500 kV/cm and ∼77.3, respectively. In particular, the flexible BaSn_0.15Ti_0.85O₃ thin films show excellent fatigue properties during the bending cycle tests. The results demonstrate that the BaSn_0.15Ti_0.85O₃ thin films prepared on copper foils are an excellent candidate for electrically tunable applications in flexible and wearable electronics.     

Dispersion and microwave processing of nano-sized ITO powder for the fabrication of transparent conductive oxides

Aqueous dispersions of tin-doped indium oxide (ITO) nanopowder were prepared and the effect of the addition of PEG 400, Tween 80 and β-alanine as dispersants was investigated using zeta potential and particle size distribution measurements. Both PEG 400 and β-alanine were found to produce stable dispersions that were used to deposit ITO thin films on glass substrates by dip and spin coating methods. The ITO thin films were heat-treated using both conventional and microwave heat treatment in order to improve the inter-particle connections and hence the resistivity and transparency of the films. All the films exhibited an average transmittance of >80% over the visible spectrum after being subjected to the heat treatment process. ITO films prepared with no dispersant showed very high resistivity values for both heating methods, however addition of 2 wt% PEG 400 to the dispersion yielded a reduction in the resistivity values to 1.4×10⁻¹ Ω cm and 3.8×10⁻² Ω cm for conventionally and microwave treated films, respectively. The surface morphological studies confirmed that addition of dispersants improved the film uniformity and inter-particle connections of the ITO films considerably.     

Realization of high transparent conductive vanadium-doped zinc oxide thin films onto flexible PEN substrates by RF-magnetron sputtering using nanopowders targets

RF-magnetron sputtering has been carried out at room temperature to deposit vanadium-doped zinc oxide (VZO) nanostructured thin films onto flexible PEN substrates. The sputtering targets of compacted VZO nanopowder have been prepared using a rapid and inexpensive Sol-Gel synthesis followed by a supercritical drying process. Structural and morphological study of VZO particles in the targets has been carried out via X-ray diffraction and Transmission Electron Microscopy (TEM). The nanostructured thin films have been characterized to analyze the structural, morphological, electrical and optical properties as a function of vanadium content from 0 to 4 at.%. Structural characterization of VZO thin films revealed that the deposited thin films have been grown preferentially along (002) and exhibit the hexagonal wurtzite structure. The cross-sectional and microstructural analysis performed by Scanning Electron Microscopy (SEM) confirms the columnar growth of nanostructures. The deposited thin films exhibit transparent behavior with transmission >70% in the visible region. It has been observed that nanostructured thin films with vanadium content of 2% have demonstrated the lowest resistivity (6.71 × 10^?4 Ω cm) with Hall mobility of 10.62 cm² V^?1 s^?1. The deposited vanadium doped nanostructured thin films would have potential applications in electronic and optoelectronic devices.     

Facile synthesis of metal organic decomposition Al-doped ZnO ink for inkjet printing and fabrication of highly transparent conductive film

In this paper, a MOD (Metal organic decomposition) Al doped ZnO (AZO) ink was directly used for inkjet printing transparent and conductive AZO films. The ink was synthesized by using zinc acetate dihydrate and aluminum nitrate nonahydrate as precursor, 1,2-diaminopropane as a complexing agent, ethyl alcohol as solution, ethyl cellulose as addition agent. The thermal decomposition behavior of the MOD ink was investigated. The various MOD AZO inks were inkjet printed and heated at different temperatures for different times. The films were studied by X-ray diffraction, scanning electron microscopy, resistivity measurements and ultraviolet–visible spectroscopy. The results demonstrated that 0.2 M AZO (2 at%) film heated at 250 °C for 120 min showed highly preferential growth along the c-axis, uniform microstructure with a resistivity of 0.03 Ω cm and high transmittance more than 90% in the visible range of the spectrum with an optical band gap at 3.326 eV.     

Room temperature sputtering deposition of high-haze Ga-doped ZnO transparent conductive thin films on self-textured bio-based poly(ethylene 2, 5-furandicarboxylate) substrates

In this work, bio-based poly(ethylene 2,5-furandicarboxylate) (PEF) films were prepared by drop-casting method and used as substrates for depositing Ga-doped ZnO (GZO) transparent conductive thin films. Results showed that the 300-nm GZO thin films deposited on PEF substrates exhibited haze values above 65% at 550 nm without post-treatment. The high haze value was because of the large surface roughness of PEF films. The total optical transmittance and electrical properties of GZO thin films on PEF were comparable to those of GZO thin films on PET. The present study provides a simple way for the sputtering deposition of high-haze transparent conductive thin films on flexible substrates.     

Sol-gel preparation of Zn-V-Mn-O thin films for low voltage varistor applications

ZnO-based thin films in the Zn-V-Mn-O system have been synthesised by a sol-gel process and characterised for use in low voltage varistor applications. The films were prepared through multi-layer deposition of a precursor solution onto indium tin oxide-coated borosilicate glass substrates by spin-coating and subsequent annealing. Current-voltage characteristics measured for the films annealed at 700 °C showed varistor action with nonlinear coefficients (α) above 4.