I. Core Characteristics: The Art of Balancing Transparency and Conductivity

• Optical Transparency: Generally, the transmittance in the visible light band (400-760nm) is required to be ≥85%, and some high-end applications (such as flexible OLED screens) need to reach more than 90%. The lower the transmittance, the darker the display effect of the device, and the lower the energy utilization efficiency (e.g., photovoltaic modules).
• Sheet Resistance (Rs): A key indicator to measure the conductivity of the film, with the unit of “ohms per square (Ω/□)”. Mainstream applications require Rs ≤100Ω/□. Among them, scenarios such as touch screens and OLEDs need to be as low as 10-50Ω/□, while scenarios such as electrostatic discharge (ESD) protection can be relaxed to 10³-10⁵Ω/□.

II. Mainstream Types: Iteration from Traditional Materials to New Technologies

1. Indium Tin Oxide (ITO) Film: The “Performance Benchmark” in Traditional Fields

• Core Composition: An n-type semiconductor film formed by using indium oxide (In₂O₃) as the matrix and doping with 5%-10% tin oxide (SnO₂).
• Performance Advantages: Optimal comprehensive performance – the visible light transmittance can reach 90%-95%, the sheet resistance can be as low as 5-10Ω/□, and it has strong chemical stability.
• Application Scenarios: Mainstream display devices (such as LCD, OLED TV/mobile phone screens), touch panels, transparent electrodes of solar cells, anti-fog glass, etc.
• Limitations: Indium (In) is a rare metal with high price and uneven resource distribution; ITO films are brittle (with an elongation at break of only about 0.5%) and cannot meet the bending requirements of flexible devices; the preparation process requires high temperatures (300-500℃), resulting in high energy consumption.

2. Fluorine-Doped Tin Oxide (FTO) Film: The “Cost-Effective Choice” in the New Energy Field

• Core Composition: A transparent conductive film formed by using tin oxide (SnO₂) as the matrix and doping with fluorine (F).
• Performance Characteristics: The visible light transmittance is 80%-85%, and the sheet resistance is 10-50Ω/□. Although it is slightly inferior to ITO, its cost is only 1/3-1/2 of that of ITO; it is also resistant to high temperatures (can withstand annealing above 600℃), acid and alkali corrosion, and has high mechanical strength.
• Typical Applications: Solar cells (especially cadmium telluride and perovskite cells), dye-sensitized cells, transparent electrodes in high-temperature environments (such as observation windows of high-temperature furnaces).
• Disadvantages: The conductivity is greatly affected by the doping concentration, and the uniformity is poor; it has strong absorption in the low-frequency band (such as the infrared region) and is not suitable for infrared-related equipment.

3. Metal Mesh Film: The “Game-Changer” in Flexible Scenarios

• Structural Principle: Using photolithography, nanoimprinting, or inkjet printing technology, a micron-level (line width 5-20μm) metal mesh (mostly made of copper, silver, aluminum) is prepared on a transparent substrate (such as PET, PI). The mesh conducts current, and the substrate ensures transparency.
• Performance Advantages: Extremely high conductivity (sheet resistance can be as low as 0.1-5Ω/□), far superior to ITO; the metal mesh has good flexibility (the bending radius can be as small as 1mm, and the resistance change rate is less than 5% after 100,000 bends), suitable for flexible screens and wearable devices; the cost is controllable (less metal is used, and low-temperature processes can be adopted).
• Application Scenarios: Flexible OLED mobile phones/foldable screens, wearable devices (such as smart bracelets, AR glasses), large-size touch screens (such as conference tablets, in-vehicle central controls).
• Challenges: If the mesh line width is greater than 20μm, “visual moiré patterns” (interference patterns generated by superposition with display pixels) are likely to appear; metals are prone to oxidation, requiring additional coating of protective layers (such as silicon nitride, silicon oxide), which increases the complexity of the process.

4. Carbon-Based Transparent Conductive Film: A “New Direction” for Environmental Protection

• Main Types: Including graphene films, carbon nanotube (CNT) films, and conductive polymer (such as PEDOT:PSS) films.
  • Graphene Film: The transmittance of single-layer graphene is 97.7%, the conductivity is close to that of metals (carrier mobility reaches 2×10⁵ cm²/(V·s)), and it has excellent flexibility and thermal conductivity; however, large-area preparation is difficult, and the resistance of single-layer films is relatively high (3-5 layers need to be stacked to reduce it to below 50Ω/□), resulting in high cost.
  • Carbon Nanotube Film: The transmittance is 85%-90%, the sheet resistance is 50-200Ω/□, it has good flexibility (the resistance change rate is less than 10% after 10,000 bends), and it is resistant to chemical corrosion; however, carbon nanotubes are prone to agglomeration, and the dispersion process needs to be optimized to ensure uniformity.
  • PEDOT:PSS Film: An organic polymer material with a transmittance of 80%-85% and a resistance of 100-500Ω/□. It can be prepared by solution coating (such as spin coating, inkjet printing) with a simple process and low cost; however, it has poor resistance to moisture and heat (the resistance is prone to increase in high-temperature and high-humidity environments) and low mechanical strength.
• Application Exploration: At present, it is mainly focused on laboratory research and development and niche applications, such as flexible sensors, low-cost touch screens, and transparent heating films (such as defogging of car rearview mirrors). In the future, it is expected to play a role in degradable electronic devices and biocompatible devices.

III. Preparation Technology: Process Selection from Laboratory to Industrialization

Physical Vapor Deposition (PVD)

• Magnetron Sputtering: In a vacuum environment, argon ions are controlled by a magnetic field to bombard the target material (such as ITO target, FTO target), so that the target atoms are deposited on the surface of the substrate to form a film. It can realize large-area uniform coating and is the first choice for industrialization, but the equipment investment is high and the energy consumption is large.

Solution Method

• Advantages: The process is simple, the cost is low, low-temperature preparation (even room temperature) is possible, and patterned coating can be realized, which is suitable for flexible substrates.
• Disadvantages: The uniformity and density of the film layer are poor, and subsequent annealing treatment is required (some processes require high temperatures).

Photolithography/Nanoimprinting

• Photolithography: Patterns are formed through photoresist and masks, and then metal is electroplated or evaporated. It has high precision (line width can be less than 1μm), but the process is complex and the cost is high.
• Nanoimprinting: The substrate is imprinted using a prefabricated template, and then metal is deposited. It has high efficiency and low cost, suitable for mass production, but the template life is limited and the precision is affected by the template.

IV. Existing Challenges and Future Development Trends

1. Core Challenges

• Performance Balance: The contradiction between high transparency and high conductivity has not been completely resolved, especially for flexible materials, where the problem of performance degradation after bending is prominent.
• Cost Control: ITO relies on rare metal indium, and the large-area preparation cost of new materials such as graphene and carbon nanotubes is high.
• Environmental Adaptability: Some materials (such as PEDOT:PSS, metal mesh) have poor resistance to moisture, heat, and oxidation, and insufficient stability during long-term use.

2. Development Trends

• Material Diversification: Reduce dependence on ITO, develop low-cost and high-performance alternative materials, such as “ITO + metal mesh” composite films (balancing high transparency and flexibility) and doped zinc oxide (ZnO)-based films (abundant resources and low cost).
• Process Innovation: Promote low-temperature, low-energy consumption, and large-area preparation processes, such as roll-to-roll magnetron sputtering (suitable for mass production of flexible substrates) and inkjet printing (realizing personalized patterned coating).
• Function Integration: Combine transparent conductive films with other functions, such as “conductivity + antibacterial”, “conductivity + anti-glare”, and “conductivity + self-healing”, to expand applications in scenarios such as medical treatment, vehicle-mounted, and outdoor equipment.
• Greenization: Develop degradable substrates (such as cellulose, polylactic acid) and environmentally friendly materials (such as indium-free and fluorine-free oxides) to reduce pollution and energy consumption in the production process.

V. Summary