Indium Tin Oxide Anode Research Articles

Polarized and Directional Electroluminescence from Organic Light‐Emitting Devices by Using a Bifunctional Meta‐Electrode

AbstractOrganic light‐emitting devices (OLEDs) with polarized and directional emission are highly desired for their promising applications in optical imaging, optical communication, and immersive visual technologies. Existing implementation methods based on free space bulk optical elements suffer from significant power loss, limiting their practical applications. Here, a bifunctional meta‐electrode is proposed by integrating a metasurface consisting of Ag periodic corrugations onto the indium tin oxide (ITO) anode to simultaneously realize the functions of charge carrier injection and photon management in the OLEDs. Highly polarized and directional light emission is demonstrated while maintaining a high device efficiency using the meta‐electrode. The electroluminescence with a polarization extinction ratio of 5 is achieved by judiciously engineering the polarization‐dependent Purcell factor of the resonant cavity constructed by the meta‐electrode. Meanwhile, the directional light emission with a divergence angle of 10° can be obtained by the efficient out‐coupling of surface plasmon‐polariton mode. The light beam can be collimated in one direction by using 1D nanogratings and in two directions by using 2D nanopillars, respectively.

Hierarchical self-constructed molecular layers of small bifunctional molecules with strong molecular dipole moments for improvement of quantum efficiency in inorganic quantum dots

Hierarchically structured self-assembled molecular layers are functionally versatile and structurally tunable, which are nanoscale molecular building blocks with a wide range of applications from biosensing systems to optoelectronic devices. Herein, we present a facile and effective strategy to fabricate hierarchical self-constructed molecular layers comprising small bifunctional molecules with strong molecular dipole moments for improvement of quantum efficiency in inorganic quantum dots (QDs) by using the cooperative interfacial self-assembly of hydrophilic bifunctional molecules on the polar electrode surface. The spontaneous construction of nanostructured molecular layers with different molecular dipole moments was simply achieved through solution-dipping and in situ interfacial self-organization of 3-mercaptopropionic acid or 1-propanethiol molecules on the surface of indium tin oxide (ITO) anode. It is experimentally revealed that these functional molecules formed uniform and ultrathin self-constructed molecular nanolayers on the ITO surface via covalent bonding, where bifunctional 3-mercaptopropionic acid molecules induced a polar molecular surface of thiol groups with strong dipole moments, whereas 1-propanethiol molecules formed a relatively hydrophobic surface of short alkyl chains with weak dipole moments. In addition, the nanoscale ultrathin nature of these molecular layers afforded high visible light transmittance comparable to that of pristine ITO substrate. The electro-optical properties of the QD cells revealed that hierarchical self-constructed molecular nanolayer with strong molecular dipole moments exhibited superior current and luminescent properties with a 162% improvement in external quantum efficiency relative to those of a conventional QD device without molecular layer. Furthermore, the self-assembled molecular nanolayer of 3-mercaptopropionic acid exhibited a higher luminescent efficiency than 1-propanethiol-based nanolayer owing to the increased hole mobility of thiol-based molecular layer with strong dipole moments.

Multiscale Fabrication Process Optimization of DFB Cavities for Organic Laser Diodes.

In the context of the quest for the Organic Laser Diode, we present the multiscale fabrication process optimization of mixed-order distributed-feedback micro-cavities integrated in nanosecond-short electrical pulse-ready organic light-emitting diodes (OLEDs). We combine ultra-short pulsed electrical excitation and laser micro-cavities. This requires the integration of a highly resolved DFB micro-cavity with an OLED stack and with microwave electrodes. In a second challenge, we tune the cavity resonance precisely to the electroluminescence peak of the organic laser gain medium. This requires precise micro-cavity fabrication performed using e-beam lithography to pattern gratings with a precision in the nanometer scale. Optimal DFB micro-cavities are obtained with 300 nm thick hydrogen silsesquioxane negative-tone e-beam resist on 50 nm thin indium tin oxide anode exposed with a charge quantity per area (i.e., dose) of 620 µC/cm2, developed over 40 min in tetramethylammonium hydroxide diluted in water. We show that the integration of the DFB micro-cavity does not hinder the pulsed electrical operability of the device, which exhibits a peak current density as high as 14 kA/cm2.

Photo-bioelectrochemical cell anodes enhanced with titanium oxide, carbon nanotubes and chlorophyll-based catalyst on different supporting materials

An important part of a photo-bioelectrochemical cell (PBEC) is the photo-biocatalyst substrate taken as anode. This study aims to explain the effect of CNT/TiO2/chlorophyll photocatalyst coated on the cellulose nanopaper (CNP) substrate on the PBEC performance and to compare the results with those obtained for the commercial indium tin oxide (ITO) glass and flexible ITO as substrates. The results showed high sheet resistance of CNP, which is 61182 Ω sq-1, which is reduced by 80 % in the presence of CNT/TiO2/Chl biocatalyst. The highest output voltage of 0.95 to 1 V was produced by coating CNT/TiO2/Chl on the flexible ITO. The maximum current density (Jmax) of 3726 mA m-2 and the highest maximum power density value of around 574 mW m-2 were obtained for illuminated CNT/TiO2/Chl on the rigid ITO anode. In dark conditions, the highest power density was observed for CNP as the supporting substrate. The photo-bioelectrochemical cell adopting CNT/TiO2/Chl and CNP as the supporting substrate material has great potential for a variety of applications, such as wearable electronics, environmental monitoring, remote or off-grid energy supply, and renewable energy systems, thereby contributing to the advancement of sustainable energy technologies.

Nanostructured solar cells based on MoO3 film deposition

Electrodeposited molybdenum oxide thin films are used as a buffer layer between the indium tin oxide (ITO) anode and the organic electron acceptor film in organic solar cells. The MoO3 films are deposited at room temperature using a solution of molybdic, acid and citric acid as complexing agents. Such electrodeposited MoO3 ultra thin films (10-20 nm) has been used as buffer layer (BF) in ITO/BF/copper phthalocyanine (CuPc)/fullerene (C60)/ aluminium tri (8-hydroxyquinoline) (Alq3)/ aluminium photovoltaic cells. It is shown that this electrodeposited MoO3 buffer layer enhances the charge transfer from CuPc to ITO through a decrease of the effective barrier, present at the interface CuPc/ITO. This improving effect is directly highlighted by the shape of the J-V curves. The kink effect, due to the barrier present at the interface ITO/organic, disappears when the electrodeposited molybdenum oxide buffer layer, is introduced at this interface, which testifies of the decrease of the barrier.

Substrate-embedded metal meshes for ITO-free organic light emitting diodes.

Organic light-emitting diodes (OLEDs) have great potential for use in large-area display and lighting applications, but their widespread adoption for large areas is hindered by the high cost and insufficient performance of indium tin oxide (ITO) anodes. In this study, we introduce an alternative anode material - a silver mesh embedded in glass - to facilitate production of large-area OLEDs. We present a facile, scalable manufacturing technique to create high aspect ratio micromeshes embedded in glass to provide the planar geometry needed for OLED layers. Our phosphorescent green OLEDs achieve a current efficiency of 51.4 cd/A at 1000 cd/m2 and reach a slightly higher external quantum efficiency compared to a standard ITO/glass reference sample. Notably, these advancements are achieved without any impact on the viewing angle of the OLEDs. These findings represent a promising advancement towards ITO-free, high-efficiency OLEDs for various high performance, large-area applications, such as lighting and displays.

Balancing Interfacial Reactions through Regulating p-Band Centers by an Indium Tin Oxide Protective Layer for Stable Zn Metal Anodes.

Metallic zinc (Zn) is considered as one of the most attractive anode materials for the post-lithium metal battery systems owing to the high theoretical capacity, low cost, and intrinsic safety. However, the Zn dendrites and parasitic side reaction impede its application. Herein, we propose a new principle of regulating p-band center of metal oxide protective coating to balance Zn adsorption energy and migration energy barrier for effective Zn deposition and stripping. Experimental results and theoretical calculations indicate that benefiting from the uniform zincophilic nucleation sites and fast Zn transport on indium tin oxide (ITO), highly stable and reversible Zn anode can be achieved. As a result, the I-Zn symmetrical cell achieves highly reversible Zn deposition/stripping with an extremely low overpotential of 9 mV and a superior lifespan over 4000 h. The Cu/I-Zn asymmetrical cell exhibits a long lifetime of over 4000 cycles with high average coulombic efficiency of 99.9 %. Furthermore, the assembled I-Zn/AC full cell exhibits an excellent lifetime for 70000 cycles with nearly 100 % capacity retention. This work provides a general strategy and new insight for the construction of efficient Zn anode protection layer.

Balancing Interfacial Reactions through Regulating p‐Band Centers by an Indium Tin Oxide Protective Layer for Stable Zn Metal Anodes

AbstractMetallic zinc (Zn) is considered as one of the most attractive anode materials for the post‐lithium metal battery systems owing to the high theoretical capacity, low cost, and intrinsic safety. However, the Zn dendrites and parasitic side reaction impede its application. Herein, we propose a new principle of regulating p‐band center of metal oxide protective coating to balance Zn adsorption energy and migration energy barrier for effective Zn deposition and stripping. Experimental results and theoretical calculations indicate that benefiting from the uniform zincophilic nucleation sites and fast Zn transport on indium tin oxide (ITO), highly stable and reversible Zn anode can be achieved. As a result, the I−Zn symmetrical cell achieves highly reversible Zn deposition/stripping with an extremely low overpotential of 9 mV and a superior lifespan over 4000 h. The Cu/I−Zn asymmetrical cell exhibits a long lifetime of over 4000 cycles with high average coulombic efficiency of 99.9 %. Furthermore, the assembled I−Zn/AC full cell exhibits an excellent lifetime for 70000 cycles with nearly 100 % capacity retention. This work provides a general strategy and new insight for the construction of efficient Zn anode protection layer.

Model development of lattice-matched p-GaInP/i-GaAs/n-GaInP hetero-junction solar cell and its performance optimization

We report an analytical model for our proposed lattice-matched hetero-junction p-GaInP/i-GaAs/n-GaInP solar cell with the incorporation of AlInP cap layer and MgF2/TiO2 anti-reflection region supported by numerical data obtained using SENTAURUS TCAD. We investigate the impact of intrinsic layer thickness, cap layer thickness, compositional variation of gallium in GaInP alloy used in p- and n-regions of pin solar cell and also studied the effect of indium tin oxide (ITO) anode contact on photovoltaic performance of solar cell in terms of performance matrices i.e., open circuit voltage (Voc), short circuit current density (Jsc), fill-factor and power conversion efficiency (PCE). Also the performance of the proposed solar cell is optimized by judiciously choosing intrinsic layer thickness, and cap layer thickness. Our proposed device featuring 2.1-μm thick i-layer, 156-nm thick cap layer with Ga0.5In0·5P/GaAs active region yields a PCE of 19.89% which turns out to be 67% improvement as compared to the conventional solar cell enabling the proposed design attractive for photovoltaic applications.

Robust and Sustainable Indium Anode Leading to Efficient and Stable Organic Solar Cells.

The fast degradation of the charge-extraction interface at indium tin oxide (ITO) poses a significant obstacle to achieving long-term stability for organic solar cells (OSCs). Herein, a sustainable approach for recycling non-sustainable indium to construct efficient and stable OSCs and scale-up modules is developed. It is revealed that the recovered indium chloride (InCl3 ) from indium oxide waste can be applied as an effective hole-selective interfacial layer for the ITO electrode (noted as InCl3 -ITO anode) through simple aqueous fabrication, facilitating not only energy level alignment to photoactive blends but also mitigating parasitic absorption and charge recombination losses of the corresponding OSCs. As a result, OSCs and modules consisting of InCl3 -ITO anodes achieve remarkable power conversion efficiencies (PCEs) of 18.92% and 15.20% (active area of 18.73 cm2 ), respectively. More importantly, the InCl3 -ITO anode can significantly extend the thermal stability of derived OSCs, with an extrapolated T80 lifetime of ≈10000 h.

P‐124: Efficiency Enhanced Top Emitting OLED‐on‐Silicon Microdisplay with Aluminum Anode

A top emitting organic light emitting diode‐on‐silicon (OLEDoS) panel with aluminum (Al) anode for high‐resolution microdisplays was proposed and fabricated. The low work function of the Al anode increases the energy barrier of the interface between the anode and hole injection layer (HIL), and has poor hole‐injection properties, which causes the low efficiency of the device. To enhance the hole‐injection characteristics of the Al anode, we applied optimized HIL and hole transportation layer (HTL) materials. The proposed single stack structure white OLED display panel with Al anode was fabricated on CMOS backplane and the white OLED device improved efficiency by up to 20 cd/A at 1000 nit, which is 90% of the level of conventional OLEDs with indium tin oxide (ITO) anode.

The Effect of the Interface Layer on the Electronic Parameters of the Light Emitting Electrochemical Cell (LEC) Device Based on Iridium (III) Complex that Calculated by Different Methods

We report a calculation of the electronic parameters and some optical measurement results of a light-emitting electrochemical cell (LEC), one of the most basic forms of electroluminescent films by modifying 4-(4-methoxy-N-naphthalen-1-ylanilino) benzoic acid (MA) as hole injection layer doped with an emissive layer that is ionic transition metal complex (Ir[dF(CF3)ppy]2(dtbpy))PF6-(Ir-iTMC). The electronic parameters of LEC device were computed using three different methods; Cheung and Cheung’s, Conventional Schottky and Norde, to evaluate the ideality factor (n), the barrier height () and the series resistance (Rs) of the LEC device. The formation on indium tin oxide (ITO) substrate was analyzed by Atomic Force Microscopy (AFM). The HOMO-LUMO energy level and electronic charge distribution of the MA molecule were computed theoretically using Chemissian software. The MA’s HOMO-LUMO energy level is determined to be EHOMO = −5.27 eV and ELUMO = −1.40 eV. The ITO surface has been modified with the Self-Assembled Monolayers (SAM) technique as an interlayer to improve the surface working function by simplifying hole injection from the ITO anode to the Hole Transport Layer (HTL) in the LEC. The Ir- iTMC complexes containing Π-conjugated bridging ligand shown better external quantum efficiency (EQE), reaching to 1.49%. The max luminance values of the bare-LEC and LEC-MA are measured as 145 cd m−2 and 1240 cd m−2, respectively.

The effect of terminal group of hole injection self-assembled monolayers on the performance of optoelectronic devices on ITO anodes

We demonstrate the effect on the performance of conventional (Indium tin oxide (ITO)/N,Nj-Di (1- naphthyl)-N,Nj-diphenyl-(1,1-biphenyl)-4,4-diamine (NPB)/Tris-(8-hydroxyquinoline)aluminum (Alq3)/LiF/Al) optoelectronic devices when the ITO surface is modified with various types of self-assembled monolayer (SAM)s such as 3-(trimethoxysilyl)propylamine (NH2SAM), Trimethoxy (propyl)silane CH3SAM, and Trimethoxy (3,3,3-trifluoropropyl)silane (F3SAM). The head functional group and chain configuration are trimethoxysilylpropyl (-(CH3O)3Si(CH2)2) and the tail groups distinguished SAMs (-NH2, -CH3, and -CF3). The contact angles of NH2SAM, CH3SAM, and F3SAM deposited on ITO and ITO were 70.7°, 81.42°, 68.23°, and 30.85°, respectively. The SAM-modified ITO's surface morphology Rpv and Rq parameters were reduced from 31.02 nm to 2.0 nm and 1.18 nm–0.26 nm. The work functions values of ITO, ITO/NH2SAM, ITO/CH3SAM and ITO/F3SAM measured by UPS were 4.99eV, 4.39, 5.09 and 5.69eV, respectively. The maximum luminance of the SAM-modified device increased to 166-fold, and the current density 105-fold, compared to the unmodified device when the operating voltage is set to 11 V. Current and power efficiency increased by 1.9 and 2-fold, respectively. The hole injection conditions are enhanced and the hole injection barrier height between ITO/NPB is reduced.

A three-stage engineered deposition rate profile in evaporation processes for ultra-thin metallic transparent conductors

Transparent conductors are employed in many optoelectronic components such as liquid crystal displays, light-emitting diodes, and solar cells. Indium-tin-oxide (ITO) is the most common transparent conductor, which suffers from difficulties such as high annealing temperature and brittleness. One of the attractive alternative solutions is to use ultra-thin metal films (UTMFs). In this study, the electrical and optical properties of ultra-thin composite metal films have been studied in terms of the effect of simultaneous controlling of the deposition rate and the doping. A three-stage deposition process using electron-beam and thermal evaporation was purposed for the fabrication of UTMFs. The three steps are: (I) deposition of an ultra-thin seed layer, (II) a co-deposition process with a precisely engineered deposition rate during the transition of the two layers, and (III) an accelerated deposition of the metallic layer at the end. A chromium ultra-thin layer was used as a seed layer, and gold or silver metal was studied in the subsequent deposition stages. The results showed that the three-deposition process could effectively improve the percolation threshold, leading to high average transparency of ≥71% over 400–700 nm, the sheet resistance of ≤22Ω/□, and roughness of ≤0.6 nm root mean square in UTMFs samples employing gold as the metal layer, where the UTMF total thickness was ≈8.3 nm. As a proof of concept, organic light-emitting diodes (OLEDs) were fabricated employing an optimized chromium-gold UTMF and also with a witness ITO. According to the results, UTMFs based on the three-stage process, provide acceptable performance in OLEDs compared to the ones exploiting the ITO anode, indicating that such UTMFs are applicable in various optoelectronic devices.

High-performance copper nanowire electrode for efficient flexible organic light-emitting diode

Highly conductive and robust polyvinyl alcohol/copper nanowire (PVA/CuNW) flexible transparent conductive electrode (FTCE) is fabricated via a simple and low-cost process at room temperature. The CuNW film is formed on a mixed cellulose ester (MCE) membrane by vacuum filtration. Subsequently, the flowing glacial acetic acid (GAA)-toluene solution passes through them to remove the oxide layer without damaging nanowires. The final PVA/CuNW FTCE is constructed by embedding the treated CuNWs into a pre-prepared PVA binding layer on the polyethylene terephthalate (PET) substrate, which presents excellent conductivity with a low sheet resistance of 46.2 Ω / s q and a high transparency of 90.5% at 550 nm. Meanwhile, the chemical and mechanical stability have been significantly enhanced compared with the bare CuNW FTCE attributed to the protective effect of the PVA binding layer. A flexible phosphorescent OLED device using such PVA/CuNW FTCE as the anode exhibits a current efficiency of 26.4 cd/A at 1000 cd/m 2 , which is comparable to that of the reference device (27.1 cd/A) based on indium tin oxide anode on glass, indicating its high potential for application in flexible optoelectronics. • Highly conductive PVA/CuNW electrodes are fabricated at room temperature. • The electrode shows excellent optoelectronic properties. • Low roughness as well as significantly enhanced chemical and mechanical stability has been achieved. • The flexible OLED device using PVA/CuNW exhibits high luminance and efficiency.

A Direct surface modification strategy of ITO anodes enables high-performance organic photodetectors

A direct modification strategy of indium tin oxide (ITO) for high-performance organic photodetectors (OPDs) is developed. By using chlorinated ITO (ITO-Cl) as the anode, the OPD device exhibits superior performance than ITO/PEDOT:PSS-based device.

Enhancement Performance of Organic Light‐Emitting Diodes Through Self‐Assembled Monolayer‐Modified ITO Anode

Herein, three self‐assembling materials (SAMs), (pyridine‐4‐ylmethyl)phosphonic acid (PyPA), benzylphosphonic acid (BnPA), and pentafluorobenzyl phosphonic acid (F5BnPA), are selected as hole‐injecting layers in organic light‐emitting diodes (OLEDs) and the effects of the aromatic ring of SAMs on indium tin oxide (ITO) work function (WF), hole injection, and device performances are investigated. After assembling them on ITO, the X‐ray photoemission spectroscopy data suggest that three samples have a similar binding mode, and the ultraviolet photoemission spectroscopy shows the effective change of ITO WF gradually enlarged along the order of PyPA, BnPA, and F5BnPA, resulting in increase in hole‐injecting capability in turn. The calculated molecule dipole of pyridine is 2.65 Debye, clearly larger than that of phenyl (0.32 Debye) and pentafluorophenyl (1.88 Debye), but PyPA presents minimum ITO WF change. Such differentiated WF changes are not only contributed by the molecular dipole of aromatic ring but also their titling angles. In OLEDs based on tris(8‐hydroxyquinoline) aluminum (III) (Alq3), the device modified by PyPA affords the highest external quantum efficiency (EQE) of 1.45% and current efficiency (CE) of 4.62 cd A−1. However, in the device using 9‐[4‐(4,6‐diphenyl‐1,3,5‐triazine‐2‐yll)phenyl]‐N,N,N′,N′‐tetraphenyl‐9H‐carbazole‐3,6‐diamine as emitters, the OLEDs modified by F5BnPA show the best EQE of 24.85% and CE of 81.88 cd A−1.

Enhancing hole-injection efficiency of top-emitting organic light-emitting diodes based on Al/MoNx anodes

High reflectivity bottom anodes are essential for high luminance efficiency top-emitting organic light-emitting diodes (TOLEDs). Although the element Al has high optical reflectivity, its poor hole-injection property severely hinders the realization of high efficient TOLED due to its low work function. In this letter, a high work function MoNx layer with different growth time was deposited on Al layers for enhancing the hole-injection efficiency of TOLEDs. Compared with the bottom-emitting OLED (BOLED) using indium-tin oxide (ITO) anode, the TOLED with Al/MoNx (8 s) anode shows a lower driving voltage of 3.1 eV than that (3.4 eV) of the BOLED at 20 mA/cm2, which may attribute to higher work function of MoNx leading to a stronger hole-injection. Moreover, the TOLED with Al/MoNx (8 s) anode exhibits higher brightness (11800 cd/m2) at 20 mA/cm2, higher maximum current efficiency (64.6 cd/A) and narrower electroluminescence spectra. These results indicate that the Al/MoNx layers could be effective hole-injection anodes for achieving high-performance TOLEDs.

UV-ozone treated Ti3C2Tx-MXene nanosheets as hole injection layer for organic light-emitting diodes

In this work, we successfully synthesized Ti3C2Tx-MXene nanosheets with a lateral dimension of 1 ∼ 2 μm by using wet-chemical etchant and sonication-assisted liquid-phase exfoliation method. After UV-ozone treatment, the work function for Ti3C2Tx-MXene nanosheets was adjusted to 5.14 eV well matching to indium tin oxide (ITO) anode (4.80 eV). Using Ti3C2Tx-MXene nanosheets as hole injection layer (HIL), Ir(ppy)3-based green organic light-emitting diodes (OLEDs) were fabricated, and the resulting devices exhibit a low turn-on voltage of 3.0 V and the high current efficiency, power efficiency and external quantum efficiency of 72.79 cd/A, 54.44 lm/W and 20.34 %, which are obviously better than these of 67.38 cd/A, 50.38 lm/W and 18.65 % for PEDOT:PSS-based reference device. Further, FIrpic- and Ir(pq)2acac-based blue and red OLEDs with Ti3C2Tx-MXene nanosheets HIL were demonstrated, which also show the significantly improved device efficiency of 44.56 cd/A, 32.44 lm/W and 22.07 % for blue device and 39.17 cd/A, 38.54 lm/W and 21.90 % for red device than these for corresponding PEDOT:PSS-based devices, proving the universal applicability of Ti3C2Tx-MXene nanosheets as HIL in OLEDs. The higher performance for Ti3C2Tx-MXene nanosheets-based devices can be attributed to the appropriate work function, high transmittance, high carrier mobility and good film forming property for Ti3C2Tx-MXene nanosheets. This is the first report about the MXene using as HIL in OLEDs, which opens up a new way to develop high-performance holes injection materials for solution-processed OLEDs.

Van der Waals Epitaxy of Thin Gold Films on 2D Material Surfaces for Transparent Electrodes: All-Solution-Processed Quantum Dot Light-Emitting Diodes on Flexible Substrates.

With the assistance of van der Waals (vdW) epitaxy, nanometer-thick and highly conductive gold films are deposited onto MoS2 surfaces for use as transparent anode electrodes in quantum dot light-emitting diodes (QLEDs) on poly(ethylene terephthalate) (PET) substrates. After transferring wafer-scale and monolayer MoS2 to PET substrates, 10 nm thick gold (Au) films are deposited onto the two-dimensional (2D) material surfaces as anode electrodes. Bounded only by weak vdW forces on 2D material surfaces, the diffusive Au adatoms tend to facilitate lateral growth and lead to the formation of continuous and highly conductive thin metal films in the nanometer regime. The Au film exhibits excellent tensile bending stability for its sheet resistance, which is superior to that of rigid indium-tin oxide (ITO) films on PET substrates. Thermally stable CdSe@CdZnS/ZnS QLEDs are fabricated on the PET substrate. Compared with devices fabricated on sapphire substrates, the phenomenon of sub-bandgap turn-on is observed for the flexible device. Based on our demonstrations, the high conductivity and robust durability toward substrate bending make the nanometer-thick Au film grown on 2D material surfaces a promising candidate to replace current ITO anode electrodes for flexible device applications.