Suppressed Interdiffusion and Degradation in Flexible and Transparent Metal Electrode-Based Perovskite Solar Cells with a Graphene Interlayer

Advances in solar energy harvesting integrated by van der Waals graphene heterojunctions

Graphene has garnered increasing attention for solar energy harvesting owing to its unique features. However, limitations hinder its widespread adoption in solar energy harvesting, comprising the band gapless in the molecular orbital of graphene lattice, its vulnerability to oxidation in oxidative environments, and specific toxic properties that require careful consideration during development. Beyond current challenges, researchers have explored doping graphene with ionic liquids to raise the lifespan of solar cells (SCs). Additionally, they have paid attention to optimizing graphene/Si Schottky junction or Schottky barrier SCs by enhancing the conductivity and work function of graphene, improving silicon's reflectivity, and addressing passivation issues at the surface/interface of graphene/Si, resulting in significant advancements in their power conversion efficiency. Increasing the functional area of graphene-based SCs and designing efficient grid electrodes are also crucial for enhancing carrier collection efficiency. Flaws and contaminants present at the interface between graphene and silicon pose significant challenges. Despite the progress of graphene/Si-based photovoltaic cells still needs to catch up to the efficiency achieved by commercially available Si p-n junction SCs. The low Schottky barrier height, design-related challenges associated with transfer techniques, and high lateral resistivity of graphene contribute to this performance gap. To maximize the effectiveness and robustness of graphene/Si-based photovoltaic cells, appropriate interlayers have been utilized to tune the interface and modulate graphene's functionality. This mini-review will address ongoing research and development endeavors using van der Waals graphene heterojunctions, aiming to overcome the existing limitations and unlock graphene's full potential in solar energy harvesting and smart storage systems.

Progress and Challenges Toward Effective Flexible Perovskite Solar Cells

The demand for building-integrated photovoltaics and portable energy systems based on flexible photovoltaic technology such as perovskite embedded with exceptional flexibility and a superior power-to-mass ratio is enormous. The photoactive layer, i.e., the perovskite thin film, as a critical component of flexible perovskite solar cells (F-PSCs), still faces long-term stability issues when deformation occurs due to encountering temperature changes that also affect intrinsic rigidity. This literature investigation summarizes the main factors responsible for the rapid destruction of F-PSCs. We focus on long-term mechanical stability of F-PSCs together with the recent research protocols for improving this performance. Furthermore, we specify the progress in F-PSCs concerning precise design strategies of the functional layer to enhance the flexural endurance of perovskite films, such as internal stress engineering, grain boundary modification, self-healing strategy, and crystallization regulation. The existing challenges of oxygen-moisture stability and advanced encapsulation technologies of F-PSCs are also discussed. As concluding remarks, we propose our viewpoints on the large-scale commercial application of F-PSCs.

Enhancing Light Extraction Efficiency in OLED Using Scattering Structure-Embedded DMD-Based Transparent Composite Electrodes

This study investigates the application of scattering structures to the metal layer in a DMD (Dielectric/Metal/Dielectric) configuration through plasma treatment. The purpose is to enhance the light extraction efficiency of organic light-emitting diodes (OLEDs). Different plasma conditions were explored to create scattering structures on the metal layer. The fabricated devices were characterized for their electrical and optical properties. The results demonstrate that the introduction of scattering structures through plasma treatment effectively improves the light extraction efficiency of OLEDs. Specifically, using O2-plasma treatment on the metal layer resulted in significant enhancements in the total transmittance, haze, and figure of merit. These findings suggest that incorporating scattering structures within the DMD configuration can effectively promote light extraction in OLEDs, leading to enhanced overall performance and light efficiency.

Highly Stable and Efficient Light-Emitting Diodes Based on Orthorhombic γ-CsPbI3 Nanocrystals

Orthorhombic γ-CsPbI₃ possesses the highest structural stability among the optically active (light-emissive) CsPbI₃ perovskites. Here, we make use of a seed-assisted heteroepitaxial growth to fabricate seed/core/shell CaI_x/γ-CsPbI₃/CaI₂ nanocrystals. Ultrasmall CaI_x nanoparticles serve as seeds to template the Pb-centered octahedral arrangement which enables the formation of the γ-CsPbI₃ phase and at the same time inhibit lattice strain by blocking the force transfer that otherwise leads to an octahedral twist and so improve the structural stability of the resulting nanocrystals. An outer shell composed from the same material, CaI₂, isolates the formed γ-CsPbI₃ nanocrystals from the environment, which also significantly improves their stability under ambient conditions. Optical and electrical studies indicate that the seed/core/shell CaI_x/γ-CsPbI₃/CaI₂ structure possesses a shallower set of trap states as compared to cubic α-CsPbI₃ nanocrystals. Light-emitting diodes utilizing these γ-CsPbI₃ nanocrystals show a record high external quantum efficiency of 25.3%, high brightness of over 13600 cd/m², and an operational lifetime of ∼14 h before reaching 50% of their initial luminance. These devices can repeatedly be illuminated over 650 times at ∼500 cd/m² with no decline of brightness, which indicates their great commercial potential.

Recent advances of two-dimensional material additives in hybrid perovskite solar cells

Perovskite solar cells (PSCs) have become one of the state-of-the-art photovoltaic technologies due to their facile solution-based fabrication processes combined with extremely high photovoltaic performance originating from excellent optoelectronic properties such as strong light absorption, high charge mobility, long free charge carrier diffusion length, and tunable direct bandgap. However, the poor intrinsic stability of hybrid perovskites under environmental stresses including light, heat, and moisture, which is often associated with high defect density in the perovskite, has limited the large-scale commercialization and deployment of PSCs. The use of process additives, which can be included in various subcomponent layers in the PSC, has been identified as one of the effective approaches that can address these issues and improve the photovoltaic performance. Among various additives that have been explored, two-dimensional (2D) materials have emerged recently due to their unique structures and properties that can enhance the photovoltaic performance and device stability by improving perovskite crystallization, defect passivation, and charge transport. Here, we provide a review of the recent progresses in 2D material additives for improving the PSC performance based on key representative 2D material systems, including graphene and its derivatives, transitional metal dichalcogenides, and black phosphorous, providing a useful guideline for further exploiting unique nanomaterial additives for more efficient and stable PSCs in the near future.

Double Layer Composite Electrode Strategy for Efficient Perovskite Solar Cells with Excellent Reverse-Bias Stability

Perovskite solar cells (PSCs) have become the representatives of next generation of photovoltaics; nevertheless, their stability is insufficient for large scale deployment, particularly the reverse bias stability. Here, we propose a transparent conducting oxide (TCO) and low-cost metal composite electrode to improve the stability of PSCs without sacrificing the efficiency. The TCO can block ion migrations and chemical reactions between the metal and perovskite, while the metal greatly enhances the conductivity of the composite electrode. As a result, composite electrode-PSCs achieved a power conversion efficiency (PCE) of 23.7% (certified 23.2%) and exhibited excellent stability, maintaining 95% of the initial PCE when applying a reverse bias of 4.0 V for 60 s and over 92% of the initial PCE after 1000 h continuous light soaking. This composite electrode strategy can be extended to different combinations of TCOs and metals. It opens a new avenue for improving the stability of PSCs.

Stabilization of Perovskite Solar Cells: Recent Developments and Future Perspectives

Exceptional power conversion efficiency (PCE) of 25.7% in perovskite solar cells (PSCs) has been achieved, which is comparable with their traditional rivals (Si-based solar cells). However, commercialization-worthy efficiency and long-term stability remain a challenge. In this regard, there are increasing studies focusing on the interface engineering in PSC devices to overcome their poor technical readiness. Herein, the roles of electrode materials and interfaces in PSCs are discussed in terms of their PCEs and perovskite stability. All the current knowledge on the factors responsible for the rapid intrinsic and external degradation of PSCs is presented. Then, the roles of carbonaceous materials as substitutes for noble metals are focused on, along with the recent research progress in carbon-based PSCs. Furthermore, a sub-category of PSCs, that is, flexible PSCs, is considered as a type of exceptional power source due to their high power-to-weight ratios and figures of merit for next-generation wearable electronics. Last, the future perspectives and directions for research in PSCs are discussed, with an emphasis on their commercialization.

Highly Efficient Self-Encapsulated Flexible Semitransparent Perovskite Solar Cells via Bifacial Cation Exchange

Flexible semitransparent perovskite solar cells (ST-PSCs) have great potential for use in high-density energy systems, such as building or vehicle integrated photovoltaics, considering the great features of PSC devices, including high performance, light weight, thin-film processability, and high near-infrared transmittance. Despite numerous efforts toward achieving efficiency and flexibility in ST-PSCs, the realization of high-performance and operational stability in ST-PSCs still require further development. Herein, we demonstrated the development of highly efficient, stable, and flexible ST-PSCs using polyimide-integrated graphene electrodes via a lamination-assisted bifacial cation exchange strategy. A high-quality perovskite layer was obtained through the cation exchange reaction using the lamination process, and ST-PSCs with 15.1% efficiency were developed. The proposed ST-PSC device also demonstrated excellent operational stability, mechanical durability, and moisture stability owing to the chemically inert and mechanically robust graphene electrodes. This study provides an effective strategy for developing highly functional ST-perovskite optoelectronic devices with high-performance and long-term operational stability.

Highly Crystalline Graphene as the Atomic 2D Blanket of a Perovskite Absorber for Enhanced Photovoltaic Performance

Perovskite solar cells (PSCs) have demonstrated enormous potential for next-generation low-cost photovoltaics. However, due to the intrinsically low bond energy of the perovskite lattice, the long-term stability is normally undermined by ion migration initiated by the electric field and atmospheric conditions. Therefore, ideal ion migration inhibition is important to achieve an enhanced stability of PSCs. Herein, we first introduce a chemical vapor deposition (CVD) fabricated highly crystalline graphene as an atomic 2D blanket directly for the perovskite absorber of PSCs. Iodine and lithium ion migration is effectively inhibited for perovskite solar cells under a continuous static electric field. The water and oxygen corrosion of the unencapsulated device has been dramatically mitigated with atomic graphene blanketing on the perovskite film. With triphenylamine (TPA) molecule modification, the photoconversion efficiencies (PCEs) of the blanketed devices reach 21.54%. The sample with blanket graphene maintains 85% of the initial efficiency, in comparison to 52% of the control sample under voltage bias. After 600 h of aging at 25 °C and 55 RH%, 86% in comparison to <30% of the PCE for the control device is obtained for the sample with a graphene blanket. Thus, we propose that crystalline graphene has an excellent and effective ion-blocking blanket potential for highly stable perovskite devices.

Effective hole conductivity in nitrogen-doped CVD-graphene by singlet oxygen treatment under photoactivation conditions

Nitrogen substitutional doping in the π-basal plane of graphene has been used to modulate the material properties and in particular the transition from hole to electron conduction, thus enlarging the field of potential applications. Depending on the doping procedure, nitrogen moieties mainly include graphitic-N, combined with pyrrolic-N and pyridinic-N. However, pyridine and pyrrole configurations of nitrogen are predominantly introduced in monolayer graphene:N lattice as prepared by CVD. In this study, we investigate the possibility of employing pyridinic-nitrogen as a reactive site as well as activate a reactive center at the adjacent carbon atoms in the functionalized C–N bonds, for additional post reaction like oxidation. Furthermore, the photocatalytic activity of the graphene:N surface in the production of singlet oxygen (¹O₂) is fully exploited for the oxidation of the graphene basal plane with the formation of pyridine N-oxide and pyridone structures, both having zwitterion forms with a strong p-doping effect. A sheet resistance value as low as 100 Ω/□ is reported for a 3-layer stacked graphene:N film.

Recent Progress of Electrode Materials for Flexible Perovskite Solar Cells

Flexible perovskite solar cells (FPSCs) have attracted enormous interest in wearable and portable electronics due to their high power-per-weight and low cost. Flexible and efficient perovskite solar cells require the development of flexible electrodes compatible with the optoelectronic properties of perovskite. In this review, the recent progress of flexible electrodes used in FPSCs is comprehensively reviewed. The major features of flexible transparent electrodes, including transparent conductive oxides, conductive polymer, carbon nanomaterials and nanostructured metallic materials are systematically compared. And the corresponding modification strategies and device performance are summarized. Moreover, flexible opaque electrodes including metal films, opaque carbon materials and metal foils are critically assessed. Finally, the development directions and difficulties of flexible electrodes are given.

Fullerene binding effects in Al(III)/Zn(II) Porphyrin/Phthalocyanine photophysical properties and charge transport

We evaluate the fullerene C₆₀ binding effect; through the metal (Al) and through the ligand (Pc,TPP), on the photophysical and charge transport properties of M-porphyrin(TPP)/phthalocyanine(Pc) (M = Al(III), Zn(II)). We perform density functional theory (DFT) and time-dependent DFT calculations for the macrocycle-C₆₀ dyads, showing that all systems studied are thermodynamically favorable. The C₆₀ binding effect on the absorption spectrum is a red-shift of the Q and Soret (B) bands of TPPs and Pcs. The Pc-dyads show longer λ for Q bands (673 nm) than those with TPP (568 nm). AlTPP-C₆₀ and ZnTPP-C₆₀ show a more favorable electron injection to TiO₂ than the analogs Pcs, and the regeneration of the dye is preferred in AlTPP-C₆₀ and AlPc-C₆₀. Zero-bias conductance is computed (10^-4-10^-7 G₀) for the dyads using molecular junctions with Au(111)-based electrodes. When a bias voltage of around 0.6 V up to 1 V is applied, an increase in current is obtained for AlTPP-C₆₀ (10^-7 A), ZnTPP-C₆₀ (10^-7 A), and AlPc-C₆₀ (10^-8 A). Although there is not a unique trend in the behavior of the dyads, Pcs have better photophysical properties than TPPs and the latter are better in the charge transport. We conclude that AlTPP(ZnTPP)-C₆₀ dyads are an excellent alternative for designing new materials for dye-sensitized solar cells or optoelectronic devices.

Biomimetic Hierarchically Silver Nanowire Interwoven MXene Mesh for Flexible Transparent Electrodes and Invisible Camouflage Electronics

Flexible transparent electrodes demand high transparency, low sheet resistance, as well as excellent mechanical flexibility simultaneously, however they still remain to be a great challenge due to"trade-off" effect. Herein, inspired by a hollow interconnected leaf vein, we developed robust transparent conductive mesh with biomimetic interwoven structure via hierarchically self-assembles silver nanowires interwoven metal carbide/nitride (MXene) sheets along directional microfibers. Strong interfacial interactions between plant fibers and conductive units facilitate hierarchically interwoven conductive mesh constructed orderly on flexible and lightweight veins while maintaining high transparency, effectively avoiding the trade-off effect between optoelectronic properties. The flexible transparent electrodes exhibit sheet resistance of 0.5 Ω sq^-1 and transparency of 81.6%, with a remarkably high figure of merit of 3523. In addition, invisible camouflage sensors are further successfully developed as a proof of concept that could monitor human body motion signals in an imperceptible state. The flexible transparent conductive mesh holds great potential in high-performance wearable optoelectronics and camouflage electronics.

Recent cutting-edge strategies for flexible perovskite solar cells toward commercialization

Flexible perovskite solar cells (f-PSCs) have attracted tremendous attention as a self-power supply for various electronic devices that require high power, various form-factors, and a light-weight power supply. In addition, many studies have investigated scalable and continuous roll-to-roll (R2R) processes, with the aim of mass production and commercialization of f-PSCs. In this review, we focus on the strategies developed in the last three years toward commercialization of high-efficiency, lightweight and ultra-flexible, and reliable perovskite solar modules (f-PSMs). Furthermore, the research perspectives of f-PSCs regarding their future development are addressed.

Cohesively Enhancing the Conductance, Mechanical Robustness, and Environmental Stability of Random Metallic Mesh Electrodes via Hot-Pressing-Induced In-Plane Configuration

Flexible transparent conductive electrode (FTCE) is highly desirable due to the fast-growing flexible optoelectronic devices. Several promising FTCEs based on metal material have been developed to replace conventional indium tin oxide (ITO). The random metal mesh is considered to be one of the competitive candidates. However, obtaining feasible random metal mesh with low sheet resistance, high transparency, good mechanical durability, and strong environmental stability is still a great challenge. Here, a random metal mesh-based FTCE with an in-plane structure, achieved by a facile hot-pressing process, is demonstrated. The hot-pressing process enables the fabrication of highly conductive FTCE with improved mechanical robustness and environmental stability. The in-plane FTCE shows a low sheet resistance of 1.63 Ω·sq^-1 with an 80.6% transmittance, low relative resistance increase (RRI) of 7.9% after 240 h 85 °C/85% RH test, and low RRI of 8.0% after 10⁵ cycles of bending test. Besides, various applications of the in-plane FTCE were demonstrated, including the flexible heater, flexible touch screen, and flexible electroluminescence. We anticipate that these results will spark interest in in-plane random metal mesh electrodes and enable the application of random metal mesh in flexible optoelectronic devices.

Application of Titanium-Carbide MXene-Based Transparent Conducting Electrodes in Flexible Smart Windows

Among various available materials used in transparent and flexible devices, MXenes are attracting attention as a brand-new candidate in this category. Ti₃C₂Tx MXene as a 2D material has exceptional properties, making it a potential material having numerous applications in different areas. Because of its high conductivity, it can be used in transparent conducting electrodes (TCEs). In this study, the MXenes etched by highly concentrated acid at 50 °C,were spin-coated on polyethylene terephthalate (PET) film and annealed at moderate temperatures up to 170 °C. The adhesion of MXene to PET was found to be remarkably improved by annealing. These TCEs exhibited a sheet resistance of ∼424 Ω/sq. and transmittance of ∼87%. The aging stability of MXene-coated PET films against oxidation under ambient conditions was studied up to 28 days and resistance change was found ∼30% during this period. The flexibility test showed low bending resistance change (∼1.5%) at 1000th cycle and cumulative resistance change of ∼20% at a bending radius of ∼3.9 mm after 1000 cycles. These transparent, flexible, and conducting electrodes were used to fabricate polymer dispersed liquid crystal (PDLC)-based flexible smart windows. The smart windows fabricated by curing PDLC mixture sandwiched between the MXene electrodes were also found flexible in ON/OFF states. The MXene-based flexible smart windows resulted in good opacity in the OFF state and high transparency in the ON state, exhibiting low threshold voltage <10 V and high transmittance ∼80% at 60 V. The flexible smart windows operated normally even at ∼4 mm bending radius.

Graphene Antiadhesion Layer for the Effective Peel-and-Pick Transfer of Metallic Electrodes toward Flexible Electronics

Owing to its exceptional physicochemical properties, graphene has demonstrated unprecedented potential in a wide array of scientific and industrial applications. By exploiting its chemically inert surface endowed with unique barrier functionalities, we herein demonstrate antiadhesive monolayer graphene films for realizing a peel-and-pick transfer process of target materials from the donor substrate. When the graphene antiadhesion layer (AAL) is inserted at the interface between the metal and the arbitrary donor substrate, the interfacial interactions can be effectively weakened by the weak interplanar van der Waals forces of graphene, enabling the effective release of the metallic electrode from the donor substrate. The flexible embedded metallic electrode with graphene AAL exhibited excellent electrical conductivity, mechanical durability, and chemical resistance, as well as excellent performance in flexible heater applications. This study afforded an effective strategy for fabricating high-performance and ultraflexible embedded metallic electrodes for applications in the field of highly functional flexible electronics.

Foldable Perovskite Solar Cells Using Carbon Nanotube-Embedded Ultrathin Polyimide Conductor

Recently, foldable electronics technology has become the focus of both academic and industrial research. The foldable device technology is distinct from flexible technology, as foldable devices have to withstand severe mechanical stresses such as those caused by an extremely small bending radius of 0.5 mm. To realize foldable devices, transparent conductors must exhibit outstanding mechanical resilience, for which they must be micrometer-thin, and the conducting material must be embedded into a substrate. Here, single-walled carbon nanotubes (CNTs)-polyimide (PI) composite film with a thickness of 7 µm is synthesized and used as a foldable transparent conductor in perovskite solar cells (PSCs). During the high-temperature curing of the CNTs-embedded PI conductor, the CNTs are stably and strongly p-doped using MoO x , resulting in enhanced conductivity and hole transportability. The ultrathin foldable transparent conductor exhibits a sheet resistance of 82 Ω sq.-1 and transmittance of 80% at 700 nm, with a maximum-power-point-tracking-output of 15.2% when made into a foldable solar cell. The foldable solar cells can withstand more than 10 000 folding cycles with a folding radius of 0.5 mm. Such mechanically resilient PSCs are unprecedented; further, they exhibit the best performance among the carbon-nanotube-transparent-electrode-based flexible solar cells.

Investigation of the Chemical Structure of Ultra-Thin Polyimide Substrate for the Xenon Flash Lamp Lift-off Technology

Lift-off is one of the last steps in the production of next-generation flexible electronics. It is important that this step is completed quickly to prevent damage to ultrathin manufactured electronics. This study investigated the chemical structure of polyimide most suitable for the Xe Flash lamp–Lift-Off process, a next-generation lift-off technology that will replace the current dominant laser lift-off process. Based on the characteristics of the peeled-off polyimide films, the Xe Flash lamp based lift-off mechanism was identified as photothermal decomposition. This occurs by thermal conduction via light-to-heat conversion. The synthesized polyimide films treated with the Xe Flash lamp–Lift-Off process exhibited various thermal, optical, dielectric, and surface characteristics depending on their chemical structures. The polyimide molecules with high concentrations of –CF₃ functional groups and kinked chemical structures demonstrated the most promising peeling properties, optical transparencies, and dielectric constants. In particular, an ultra-thin polyimide substrate (6 μm) was successfully fabricated and showed potential for use in next-generation flexible electronics.

Single-Step Direct Growth of Graphene on Cu Ink toward Flexible Hybrid Electronic Applications by Plasma-Enhanced Chemical Vapor Deposition

Highly customized and free-formed products in flexible hybrid electronics (FHE) require direct pattern creation such as inkjet printing (IJP) to accelerate product development. In this work, we demonstrate the direct growth of graphene on Cu ink deposited on polyimide (PI) by means of plasma-enhanced chemical vapor deposition (PECVD), which provides simultaneous reduction, sintering, and passivation of the Cu ink and further reduces its resistivity. We investigate the PECVD growth conditions for optimizing the graphene quality on Cu ink and find that the defect characteristics of graphene are sensitive to the H₂/CH₄ ratio at higher total gas pressure during the growth. The morphology of Cu ink after the PECVD process and the dependence of the graphene quality on the H₂/CH₄ ratio may be attributed to the difference in the corresponding electron temperature. Therefore, this study paves a new pathway toward efficient growth of high-quality graphene on Cu ink for applications in flexible electronics and Internet of Things (IoT).

Progress in Materials Development for Flexible Perovskite Solar Cells and Future Prospects

The perovskite solar cells (PSCs) have emerged as an established technology during the last decade, with the record efficiency of such solar cells having increased from 3.8 % to 25.5 %. Recently, flexible perovskite solar cells (fPSCs) have received much attention from the academic and the industrial communities, owing to their potential for various niche applications, including portable electronics, wearable power sources, electronic textiles, and large-scale industrial roofing. fPSCs are lightweight, bendable, and suitable for roll-to-roll industrial production and can be integrated easily over any surface. This Review discusses the recent development of materials for fPSCs based on various flexible substrates, including plastic, metal, and other flexible substrates, as well as fiber-shaped perovskite solar cells, with a focus on the device structure, material selection for each layer, mechanical flexibility and the environmental stability of the fPSC devices. Finally, future applications and the outlook for fPSCs are also discussed.

The bimetallic and the anchoring group effects on both optical and charge transport properties of hexaphyrin amethyrin

Bimetallic Cu(ii)-hexaphyrin amethyrin proposed as a molecular switch operated by the application of an external magnetic field.

Scalable Fabrication of Scratch-Proof Transparent Al/F-SnO2 Hybrid Electrodes with Unusual Thermal and Environmental Stability

Fabrication protocols of transparent conducting electrodes (TCEs), including those which produce TCEs of high values of figure of merit, often fail to address issues of scalability, stability, and cost. When it comes to working with high-temperature stable electrodes, one is left with only one and that too, an expensive choice, namely, fluorine-doped SnO₂ (FTO). It is rather difficult to replace FTO with a low-cost TCE due to stability issues. In the present work, we have shown that an Al nanomesh fabricated employing the crack template method exhibits extreme thermal stability in air even at 500 °C, compared with that of FTO. In order to fill in the non-conducting island regions present in between the mesh wires, a moderately conducting material SnO₂ layer was found adequate. The innovative step employed in the present work relates to the SnO₂ deposition without damaging the underneath Al, which is a challenge in itself, as the commonly used precursor, SnCl₂ solution, is quite corrosive toward Al. Optimization of spray coating of the precursor while the Al mesh on a glass substrate held at an appropriate temperature was the key to form a stable hybrid electrode. The resulting Al/SnO₂ electrode exhibited an excellent transparency of ∼83% at 550 nm and a low sheet resistance of 5.5 Ω/□. SnO₂ coating additionally made the TCE scratch-proof and mechanically stable, as the adhesion tape test showed only 8% change in sheet resistance after 1000 cycles. Further, to give FTO-like surface finish, the SnO₂ surface was fluorinated by treating with a Selectfluor solution. As a result, the Al/F-SnO₂ hybrid film exhibited one order higher surface conductivity with negligible sensitivity toward humidity and volatile organics, while becoming robust toward neutral electrochemical environments. Finally, a custom-designed projection lithography technique was used to pixelate the Al/SnO₂ hybrid film for optoelectronic device applications.

Review of fabrication methods of large-area transparent graphene electrodes for industry

Graphene is a two-dimensional material showing excellent properties for utilization in transparent electrodes; it has low sheet resistance, high optical transmission and is flexible. Whereas the most common transparent electrode material, tin-doped indium-oxide (ITO) is brittle, less transparent and expensive, which limit its compatibility in flexible electronics as well as in low-cost devices. Here we review two large-area fabrication methods for graphene based transparent electrodes for industry: liquid exfoliation and low-pressure chemical vapor deposition (CVD). We discuss the basic methodologies behind the technologies with an emphasis on optical and electrical properties of recent results. State-of-the-art methods for liquid exfoliation have as a figure of merit an electrical and optical conductivity ratio of 43.5, slightly over the minimum required for industry of 35, while CVD reaches as high as 419.