Transparent Metal Electrode Research Articles

Revealing the Polarizations of Molecular Ferroelectrics via SHG Polarimetry at the Nanoscale.

Multifarious molecular ferroelectrics with multipolar axial characteristics have emerged in recent years, enriching the scenarios for energy harvesting, sensing, and information processing. The increased polar axes have enhanced the urgency of distinguishing different polarization states in material design, mechanism exploration, etc. However, conventional methods hardly meet the requirements of in situ, fast, microscale, contactless, and nondestructive features due to their inherent limitations. Herein, SHG polarimetry is introduced to probe the multioriented polarizations on a nanosized multiaxial molecular ferroelectric, i.e., TMCM-CdCl3 nanoplates, as an example. Combined with the analysis of the second-order susceptibility tensor, SHG polarimetry could serve as an effective method to detect the polarization orders and domain distributions of molecular ferroelectrics. Profiting from the full-optical feature, SHG polarimetry can even be performed on samples covered by transparent mediums, 2D materials, or thin metal electrodes. Our research might spark further fundamental studies and expand the application boundaries of next-generation ferroelectric materials.

Carbon-Based Electrodes for Organic Solar Cells.

Organic solar cells (OSCs) are a promising low-cost thin-film photovoltaic technology while the fabrication of transparent conductive oxide (TCO) and metal electrodes still remains a factor that hinders the scaling-up and commercialization of OSCs. Carbon-based materials are regarded as potential alternatives due to their excellent properties, such as low cost, solution processibility, high conductance, and good chemical stability. In this mini-review, the recent progress of carbon-based materials such as graphite, carbon nanosheets, graphene, and carbon nanotubes to replace the TCO and metal electrodes of OSCs is surveyed. The preparation methods of different carbon-based materials are also discussed. Based on current progress, we summarize the outlooks and challenges of carbon-based electrodes. We anticipate this mini-review will inspire more research efforts to develop high-performance and OSC-matched carbon materials for more efficient and stable carbon-electrode-based OSCs.

Stable Ultrathin Ag Electrodes by Tailoring the Surface of Plastic Substrates for Flexible Organic Light-Emitting Devices.

Flexible transparent metal electrodes (FTMEs) have significant application potentials in the fields of flexible optoelectronic devices due to their outstanding optical transmittance and electrical conductivity. However, obtaining excellent optoelectrical properties and mechanical flexibility of FTMEs is challenging because ultrathin metal layers usually follow an island growth mode. In this paper, flexible transparent ultrathin Ag electrodes with high mechanical stability and good optoelectrical properties were exploited by tailoring the surface properties of plastic substrates with ultraviolet-ozone (UVO) treatment for regulating the nucleation and growth kinetics of Ag films. The composite transparent electrodes of Ag (9 nm)/MoO3 (20 nm) fabricated on the UVO-treated polyethylene terephthalate (PET) substrates possess a low sheet resistance of ∼7.9 Ω/sq, a high optical transmittance of ∼87.2% at 550 nm, a long-period environmental stability of 30 days (∼65 °C, ∼80% humidity), and excellent mechanical flexibility of 100,000 bending cycles at a bending radius of 1.5 mm. These properties are derived from the surface treatment of PET substrates by UVO, which increases substrate surface energy and produces chemical nucleation sites of the phenolic hydroxyl groups. The phenolic hydroxyl groups generated on the PET surface not only provided efficient nucleation sites for subsequent Ag film growth but also formed C-O-Ag bonds between the substrate surface and the Ag layer, which act as "anchor chains" to fix firmly the Ag atoms on the substrate surface. As a universal applicability strategy, the composite electrodes on the UVO-treated polyethylene naphthalate (PEN) and norland optical adhesive 63 (NOA63) substrates also possess excellent optoelectrical properties and mechanical flexibility. Based on the ultrathin Ag composite electrodes, the flexible white organic light-emitting devices with PET, PEN, and NOA63 as substrates present the maximum current efficiencies of 53.0, 77.0, and 65.2 cd/A, respectively.

Solution process formation of high performance, stable nanostructured transparent metal electrodes via displacement-diffusion-etch process

Transparent electrodes (TEs) with high chemical stability and excellent flexibility are critical for flexible optoelectronic devices, such as photodetectors, solar cells, and light-emitting diodes. Ultrathin metal electrode (thickness less than 20 nm) has been a promising TE candidate, but the fabrication can only be realized by vacuum-based technologies to date, and require tedious surface engineering of the substrates, which are neither ideal for polymeric based flexible applications nor suitable for roll-to-roll large-scale manufacture. This paper presents high-performance nanostructured transparent metal electrodes formation via displacement–diffusion-etch (DDE) process, which enables the solution-processed sub-20-nm-thick ultrathin gold electrodes (UTAuEs) on a wide variety of hard and soft substrates. UTAuEs fabricated on flexible polyethylene terephthalate (PET) substrates show a high chemical/environmental stability and superior bendability to commercial flexible indium–tin-oxide (ITO) electrodes. Moreover, flexible organic solar cells made with UTAuEs show similar power conversion efficiency but much enhanced flexibility, in comparison to that of ITO-based devices.

Recent Progress on Emerging Transparent Metallic Electrodes for Flexible Organic and Perovskite Photovoltaics

The rapid development of smart and wearable electronics calls for revolutionizing optoelectronics to become flexible, lightweight, and affordable. To meet these demands in photovoltaic devices, that is, solar cells, it is essential to develop mechanically flexible transparent electrodes over the conventional rigid ones while features such as low‐temperature procedures, stability, solution process, and/or low cost are highly desired and often required. Moreover, the optoelectronic properties of an electrode must not be compromised in an operational flexible cell. Despite the considerable challenges, various bendable transparent electrodes for solar cells have emerged in recent years. Particularly, transparent electrodes based on metallic materials are especially attractive as metal offers excellent conductivity and their formation processing is generally mature and commercially viable. This work aims to provide an overview of the recent development of metal‐based transparent electrodes for flexible organic and perovskite photovoltaics. After the introduction, metallic materials for the transparent electrodes including nanowires, meshes/grids, and films are discussed. The procedures and protocols for cell flexibility testing are summarized, before highlighting recent progress on fully functional, high‐efficiency flexible organic and perovskite solar cells using these transparent metallic electrodes. Finally, the challenges and outlook of the research field are discussed.

Simulation of AlGaN MSM detector for investigating the effect varying absorber layer thickness

For detecting feeble Ultra-Violet (UV) signals it is essential that front-illuminated photodetector (PD) should havethick photo-absorbing layer with thin transparent metal electrodes and antireflective coating (ARC) so as to getmore photocurrent and low dark current.Since detector geometry influences its performance, so it is very important to optimize layer thickness parameters. In proposed work fixed area Al0.5Ga0.5N/AlN/ Sapphire based Metal-Semiconductor-Metal (MSM)PDbased has been analyzed for optimum value of active layer thickness and inter-electrode thickness.In addition to take benefit of large Schottky barrierGold material has beenutilized for electrodes. It has been illustrated in past research studies that with the increase in thickness of AlGaN layer, more incident energy can be absorbed for large EHPs generation which lead to increased responsivity.However, few research papers have related the effect of variations inthickness of active layerwith electron velocity which has significant effect on dark current density, recombination rateand additionally on efficiency.So for further development and widespread implementation of AlGaN/GaN based detectors there is need to study the effect of variation in photo-absorber layer thickness on closely related performance parameters so as to select its optimum value.Current Voltage (IV)-characteristics,recombination rate, current density plots and spectral response have been investigated using Atlas-Silvaco simulation tool.In addition for electrode thickness variation,transmission and absorptionplots are alsoinvestigated. For the proposed MSM structure, it has been observed that dark current density tends to increase
 
 beyond the optimum value of thickness of AlGaN layerwith specific absorption coefficient. Good transmission of light with high spectral response can be obtained with optimum value of electrode thickness.These observations can be suitable for improving the detectivity in support of various UV detection applications requiring good sensitivity and high signal to noise ratio.

An unexpected role of atomic oxygen dopants in Au evolution from clusters to a layer

Structure engineering is essential for manipulating the chemical, electrical, and optical properties of Au. However, it is challenging to design nanoscopic structures because no effective method is available to deviate from the intrinsic evolution behavior during and after synthesis via vapor deposition. Here, we propose an approach that utilizes the oxidation-induced clustering and layering of Au due to the strong O interference at the outmost surfaces of nanoscopic Au geometries. This promotes the evolution of Au clusters and layers that are highly wetted on their oxide supports. A 4-nm-thick epitaxial Au layer eventually evolved from the proposed growth mode, simultaneously exhibiting higher optical transparency than Ag, a near-bulk resistivity of 8 × 10−8 Ω m, and extreme resilience to chemical corrosion and mechanical deformation. This result provides a definite solution to transparent metal electrodes that are highly vulnerable to degradation in ambient and working environments.

Embedded Nickel-Mesh Transparent Electrodes for Highly Efficient and Mechanically Stable Flexible Perovskite Photovoltaics: Toward a Portable Mobile Energy Source.

The rapid development of Internet of Things mobile terminals has accelerated the market's demand for portable mobile power supplies and flexible wearable devices. Here, an embedded metal-mesh transparent conductive electrode (TCE) is prepared on poly(ethylene terephthalate) (PET) using a novel selective electrodeposition process combined with inverted film-processing methods. This embedded nickel (Ni)-mesh flexible TCE shows excellent photoelectric performance (sheet resistance of ≈0.2-0.5 Ω sq-1 at high transmittance of ≈85-87%) and mechanical durability. The PET/Ni-mesh/polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS PH1000) hybrid electrode is used as a transparent electrode for perovskite solar cells (PSCs), which exhibit excellent electric properties and remarkable environmental and mechanical stability. A power conversion efficiency of 17.3% is obtained, which is the highest efficiency for a PSC based on flexible transparent metal electrodes to date. For perovskite crystals that require harsh growth conditions, their mechanical stability and environmental stability on flexible transparent embedded metal substrates are studied and improved. The resulting flexible device retains 76% of the original efficiency after 2000 bending cycles. The results of this work provide a step improvement in flexible PSCs.

Broad spectral responsivity in highly photoconductive InZnO/MoS2 heterojunction phototransistor with ultrathin transparent metal electrode

An amorphous InZnO/MoS2 heterojunction-based phototransistor with excellent photoconductive gain and responsivity over the entire visible range has been demonstrated. The photogenerated current of the InZnO phototransistor at long light wavelength (>600 nm) was significantly improved by utilizing narrow bandgap MoS2 as the capping layer (1.3 eV). At lower wavelength, photocarriers are generated due to the optical absorption of both InZnO and MoS2 layers, whereas the latter ensures significant photocarrier generation even at the higher wavelength region of the visible spectrum. The photogenerated carriers subsequently transfer to the underlying InZnO layer of superior carrier mobility that has a high channel conduction of additional electrons from the optically-induced doubly positively charged oxygen vacancies (Vo++) where the gate field is screening, thereby leading to the higher photoconductive gain of the InZnO/MoS2 phototransistors. The dynamic photosensitivity behaviour of the aforesaid phototransistor reveals the presence of persistent photoconductivity (PPC) due to the oxygen vacancy associated with InZnO which can be removed by applying a reset gate pulse from −15 to +5 V. The optical properties of these phototransistors were further enhanced by replacing the opaque Ti/Au electrode by an ultrathin transparent Ti/Au electrode. Utilization of the transparent electrode results in enhanced electron injection from source to channel due to a reduced barrier height under illumination giving rise to a ten-fold improvement in the photocurrent and responsivity of the phototransistors. A position-dependent study of the photocurrent w.r.t beam position also reveals that the enhancement in photocurrent is strongly dependent on the position and is at its maximum when the beam is placed near the source region.

Toward wearable electronics: A lightweight all-solid-state supercapacitor with outstanding transparency, foldability and breathability

Wide applications of smart wearable electronics have triggered tremendous needs for energy storage devices featuring lightweight, transparency, foldability and breathability. However, conventional supercapacitor electrodes are always substrate-supported with a compact film structure, which strongly limits their air permeability, flexibility and transparency. In this report, we demonstrate the use of a freestanding, ultrathin (∼ 6 μm), highly conductive (4 × 105 S/m), highly transparent (> 91%), air permeable (2600 mm/s at 10 Pa) and foldable metallic mesh electrode, decorated with active MnO2 microstructures, as a breathable, transparent and foldable supercapacitor electrode. By introducing Au nanoparticles as the “nanoglue” between Ni and MnO2, excellent electrochemical performances including large areal capacitance (268 mF/cm2) and high cycling stability (90.1% capacitance retention after 10000 cycles) are obtained in the MnO2-Au-Ni mesh electrode. Furthermore, the assembled all-solid-state supercapacitor device delivers high optical transparency (∼83.6%), high air permeability (45.4 mm/s at 100 Pa), superior electrochemical performances and can withstand various deformations including bending, folding, and crumpling. The present freestanding mesh structure electrode could be further explored and applied in more potential applications, such as ion batteries, wearable sensors, and conformal healthcare devices.

Flexible devices fabricated by a plate-to-roll nanoimprint lithography system

A plate-to-roll nanoimprint lithography (P2RNIL) system has been developed to realize a high-speed, large-scale and high-resolution nanoimprint process. Imprinted patterns have been achieved with a linewidth of less than 75 nm at a speed of 22 cm2 s−1 on flexible substrate. To improve the quality of the imprinted patterns, we have proposed a compliant mechanism which can realize passive alignment and minimize the lateral displacement between template and substrate. Finite element analysis of this compliant mechanism was carried out. By using the P2RNIL system, wire-grid polarizers (up to a 10 030:1 extinction ratio and up to 88% transmittance) and transparent metal electrodes whose performance is in good accordance with simulated results were successfully fabricated.

마이크로/나노 패터닝 공정 생산성 향상 기술 동향

The purpose of this review paper is to highlight recent efforts and achievements to realize high productivity of micro/nano structure fabrication processes and feasible applications. Due to development in micro/nano fabrication processes, demands on micro/nano related applications are increasing rapidly in various fields. To meet requirements, fabrication process must have high production yield and be automated. Also, fabricated micro/nano structures are expressed on large area substrate. So, it is timely and appropriate to move forward to a new epoch by researching more robust and high throughput fabrication methods, large area fabrication techniques, and new applications. In this review paper, we present a series of recent achievements to overcome some of the limitations in productivity and product size of current fabrication processes, such as photolithography and imprinting lithography. For potential applications, transparent metal electrode, large size optical film, bus wire for narrow bezel, and water collecting surface, are briefly described to expand the application field from the well-known.

Efficient Semitransparent Perovskite Solar Cells Using a Transparent Silver Electrode and Four-Terminal Perovskite/Silicon Tandem Device Exploration

Four-terminal tandem solar cells employing a perovskite top cell and crystalline silicon (Si) bottom cell offer a simpler pathway to surpass the efficiency limit of market-leading single-junction silicon solar cells. To obtain cost-effective top cells, it is crucial to develop transparent conductive electrodes with low parasitic absorption and manufacturing cost. The commonly used indium tin oxide (ITO) shows some drawbacks, like the increasing prices and high-energy magnetron sputtering process. Transparent metal electrodes are promising candidates owing to the simple evaporation process, facile process conditions, and high conductivity, and the cheaper silver (Ag) electrode with lower parasitic absorption than gold may be the better choice. In this work, efficient semitransparent perovskite solar cells (PSCs) were firstly developed by adopting the composite cathode of an ultrathin Ag electrode at its percolation threshold thickness (11 nm), a molybdenum oxide optical coupling layer, and a bathocuproine interfacial layer. The resulting power conversion efficiency (PCE) is 13.38% when the PSC is illuminated from the ITO side and the PCE is 8.34% from the Ag side, and no obvious current hysteresis can be observed. Furthermore, by stacking an industrial Si bottom cell (PCE = 14.2%) to build a four-terminal architecture, the overall PCEs of 17.03% (ITO side) and 11.60% (Ag side) can be obtained, which are 27% and 39% higher, respectively, than those of the perovskite top cell. Also, the PCE of the tandem cell has exceeded that of the reference Si solar cell by about 20%. This work provides an outlook to fabricate high-performance solar cells via the cost-effective pathway.

Highly transparent metal electrodes via direct printing processes

Transparent platinum electrodes are prepared using nanoimprint lithography of a newly developed molecular platinum complex. Thermal decomposition at moderate temperature of this complex gives rise to elemental platinum line and grid pattern with linewidths down to 40nm. These electrodes exhibit transmittances of 90% and resistances below 100Ω. Thus, for the first time, highly transparent electrodes are prepared by a direct soft lithographical printing process.

Freestanding transparent metallic network based ultrathin, foldable and designable supercapacitors

A freestanding transparent metallic network electrode is designed, fabricated and integrated for ultrathin, foldable and designable supercapacitor devices.

Shape Control of Periodic Metallic Nanostructures for Transparent Conductive Films

The transmittance limitations of metallic nanomeshes with hexagonally ordered perforations that are typically prepared by conventional nanosphere lithography (NSL) were demonstrated. Specially, the optoelectronic properties of perforated metallic films with continuously varying morphologies, ranging from spherical apertures to egg-shaped apertures, zigzag wires and approximate straight wires to metallic crosswire grids, are investigated, shedding light on the dependence of the optoelectronic properties on subtle changes of the film morphology especially on its periodicity. Further, to exploit both the high transmittance of these nanowires and the low sheet resistance of the nanomesh, we have developed a novel transparent metal electrode composed of two overlapping nanowire arrays via a stepwise ARNSL method. This sophisticated electrode has an increased optoelectronic performance with a sheet resistance of 100 ω sq and an average optical transmittance of 80% and is hopeful to be further improved. The stepwise ARNSL method addresses the challenges of fabricating intercrossed pattern from parallelly aligned conductive wires arrays, which are significant in constructing nanowire devices. These findings provide useful insights in the design and fabrication of unique 2D metallic electrodes for potential high-performance transparent electrode application in the transparent electronics.

Transmission enhancement based on strong interference in metal-semiconductor layered film for energy harvesting.

A fundamental strategy to enhance optical transmission through a continuous metallic film based on strong interference dominated by interface phase shift is developed. In a metallic film coated with a thin semiconductor film, both transmission and absorption are simultaneously enhanced as a result of dramatically reduced reflection. For a 50-nm-thick Ag film, experimental transmission enhancement factors of 4.5 and 9.5 are realized by exploiting Ag/Si non-symmetric and Si/Ag/Si symmetric geometries, respectively. These planar layered films for transmission enhancement feature ultrathin thickness, broadband and wide-angle operation, and reduced resistance. Considering one of their potential applications as transparent metal electrodes in solar cells, a calculated 182% enhancement in the total transmission efficiency relative to a single metallic film is expected. This strategy relies on no patterned nanostructures and thereby may power up a wide spectrum of energy-harvesting applications such as thin-film photovoltaics and surface photocatalysis.

Degradation of Flexible, ITO-Free Oligothiophene Organic Solar Cells.

We investigate the degradation of organic solar cells based on an oligothiophene (DCV5T-Me) small molecule donor and the acceptor C60. Two different flexible, transparent bottom electrode types are employed: a transparent metal electrode (TME) and silver nanowires (AgNWs). They exhibit high optical transparency up to 86% and a sheet resistance as low as 12Ω/□. Power conversion efficiencies of 7.0%, 5.7%, and 7.2% on TME, AgNWs, and indium tin oxide (ITO, reference) are reached, respectively. The solar cells are protected against moisture ingress utilizing a flexible alumina thin-film, exhibiting water vapor transmission rates down to 3 × 10(-5) g m(-2) day(-1) at 38 °C and 90% relative humidity (RH). Implementation of this ultrabarrier as top and bottom encapsulation enables fabrication of fully flexible devices. A decrease in PCE to 80% of initial values is observed after 1000 ± 50 h on flexible, encapsulated TME but only 20 ± 5 h on AgNWs in a climate of 38 °C/50% RH. Degradation in AgNW-based devices is attributed to electrode decomposition.

Working from Both Sides: Composite Metallic Semitransparent Top Electrode for High Performance Perovskite Solar Cells.

We report herein perovskite solar cells using solution-processed silver nanowires (AgNWs) as transparent top electrode with markedly enhanced device performance, as well as stability by evaporating an ultrathin transparent Au (UTA) layer beneath the spin-coated AgNWs forming a composite transparent metallic electrode. The interlayer serves as a physical separation sandwiched in between the perovskite/hole transporting material (HTM) active layer and the halide-reactive AgNWs top-electrode to prevent undesired electrode degradation and simultaneously functions to significantly promote ohmic contact. The as-fabricated semitransparent PSCs feature a Voc of 0.96 V, a Jsc of 20.47 mA cm(-2), with an overall PCE of over 11% when measured with front illumination and a Voc of 0.92 V, a Jsc of 14.29 mA cm(-2), and an overall PCE of 7.53% with back illumination, corresponding to approximately 70% of the value under normal illumination conditions. The devices also demonstrate exceptional fabrication repeatability and air stability.

Interfacial adhesion enhancement of ink-jet printed transparent metallic grid electrodes induced by the coffee-ring effect

An effective strategy was developed to regulate the surface characteristics of silver nanoparticles and enormously enhance interfacial adhesion between transparent metal grids and substrates based on the coffee-ring effect.