Ultrasonic Spray Coating for Transparent Conductive Films

 Deposition of materials such as silver nanowires, carbon nanotubes, and PEDOT:PSS

In today’s era of rapid development in flexible electronics, optoelectronic displays, and new energy industries, transparent conductive films, as a key functional material, directly determine the performance of related devices through their performance and fabrication processes. Traditional film-forming methods, such as spin coating, blade coating, or vapor deposition, are either limited by material utilization or struggle to achieve uniform coverage on large-area substrates, and are inadequate for flexible and irregularly shaped substrates. Ultrasonic spray coating technology, as an emerging precision deposition process, offers a highly promising technological path for the fabrication of high-performance transparent conductive films due to its unique advantages.

Core Technology: The Working Principle and Essence of Ultrasonic Spray Coating

The core of ultrasonic spray coating technology lies in its “ultrasonic atomization” mechanism. Unlike traditional pneumatic spraying that relies on high-pressure gas to break up liquids, ultrasonic spraying equipment converts high-frequency electrical energy into mechanical vibration through piezoelectric transducers. This high-frequency vibration is transmitted to the nozzle tip, causing the flowing spray liquid (such as a nanomaterial dispersion) to form extremely fine capillary waves on the surface. Ultimately, due to immense acceleration, it is “torn” into uniform droplets at the micron or even nanometer scale.

This principle brings several fundamental advantages:

1. Uniform and controllable droplet size: The generated droplet size distribution range is extremely narrow, ensuring a highly consistent material quantity at every “point” during the deposition process. This is the foundation for achieving high film uniformity.

2. Low velocity and weak impact: The droplets rely solely on their own inertia and a slight carrier gas to guide them towards the substrate, resulting in kinetic energy far lower than that of pneumatic spraying. This means that it has minimal impact on the formed underlying film or structurally complex substrates (such as nanowire networks), effectively avoiding the “scouring effect” and structural damage.

3. Extremely High Material Utilization: The spraying path and range can be precisely controlled by the program, ensuring that almost all atomized material is guided to the effective area of ​​the substrate, achieving a utilization rate of over 90%. This is crucial for expensive nanomaterials (such as silver nanowires).

Material System: An Ideal Deposition Platform for Diverse Transparent Conductive Materials

The gentle and uniform characteristics of ultrasonic spraying make it an ideal choice for depositing a variety of emerging transparent conductive materials, perfectly suited to diverse material systems that surpass traditional indium tin oxide (ITO).

1. Silver Nanowires: As the most promising ITO alternative, silver nanowires achieve conductivity through an interwoven network, while the porosity between the networks ensures high light transmittance. However, spin coating is prone to uneven nanowire orientation and stacking due to centrifugal force; blade coating is more sensitive to wire length and easily causes agglomeration. Ultrasonic spraying, with its low-energy droplets, can uniformly “spray” a silver nanowire dispersion onto a substrate. Under the surface tension of the solvent, the nanowires naturally settle and overlap, forming a conductive network with better connectivity and fewer defects. This results in higher transmittance for the same sheet resistance, or lower resistance for the same transmittance.

2. Carbon Nanotubes (CNTs): Single-walled or multi-walled carbon nanotubes also rely on forming a percolation network to conduct electricity. Ultrasonic spraying not only achieves uniform CNT distribution but also helps to orient the carbon nanotubes to a certain extent during deposition, reducing high contact resistance caused by disordered entanglement. Simultaneously, layer-by-layer spraying or blending with other materials can effectively fill network gaps, improving the film’s density and conductive uniformity.

3. PEDOT:PSS (Aqueous Conductive Polymer Dispersion): These materials are known for their excellent flexibility, solution processability, and high transmittance. However, during film formation, the conductivity of PEDOT:PSS is highly susceptible to influences from film morphology and phase separation. Ultrasonic spraying, by precisely controlling the droplet drying process, can promote the formation of microstructures in PEDOT and PSS that are more conducive to charge transport. Furthermore, researchers often utilize ultrasonic spraying for secondary processing, such as spraying a post-treatment solution containing trace amounts of solvent (e.g., ethylene glycol, dimethyl sulfoxide) onto the PEDOT:PSS film. Precise dosage control allows for “optimization” of the film, significantly improving its conductivity without compromising its integrity.

More importantly, ultrasonic spraying technology provides unprecedented convenience for the composite and stacking of these materials. It facilitates the sequential deposition of “sandwich” structures (such as CNT/PEDOT:PSS/AgNW) or the direct mixing and single-pass spraying of dispersions of different materials, utilizing synergistic effects to prepare composite transparent electrodes with superior overall performance (conductivity, light transmittance, flexibility, and stability).

Process Advantages: A Key to Industrialized Production

From the laboratory to large-scale production, ultrasonic spraying technology demonstrates its powerful process adaptability.

* Exceptional Uniformity and Consistency: Whether on small silicon wafers or large glass substrates with diagonal lengths exceeding one meter, ultrasonic spraying ensures remarkable consistency in film thickness and sheet resistance, with intra-wafer and inter-wafer variations controlled to extremely low levels.

* Unparalleled Patterning Capability: Combined with a mask or directly linked to a motion platform, ultrasonic spraying can easily achieve complex and precise patterned deposition without subsequent subtractive processes such as laser etching, avoiding material waste and potential structural damage. This is crucial for applications such as electrode circuits for touchscreens and fine metal meshes for OLEDs.

* Wide Substrate Adaptability: Its gentle deposition characteristics enable it to handle rigid glass, flexible PET/PC/PEN plastic films, and even special substrates such as paper and textiles that are not heat-resistant or impact-resistant, greatly expanding the application scenarios for transparent electrodes.

* Precisely Adjustable Process Parameters: Numerous parameters, such as atomization frequency, flow rate, nozzle-substrate distance, moving speed, and substrate temperature, can be independently and precisely controlled. This provides a vast “parameter space” for thin film optimization under different materials and application scenarios, facilitating the development of thin film products with extreme performance limits.

Application Prospects and Future Outlook

Based on the above advantages, transparent conductive films prepared using ultrasonic spraying technology have demonstrated great potential in many cutting-edge fields:

* Flexible Displays and Touchscreens: Providing bend-resistant and highly reliable transparent electrodes for foldable and rollable display devices.

* Organic Photovoltaics and Perovskite Solar Cells: Serving as top or bottom electrodes for cells, enabling high-efficiency, low-cost solution-based preparation, especially suitable for future large-scale roll-to-roll production processes.

* Transparent Heating Films: Capable of fabricating fast-response, uniformly heated automotive windshields, aircraft windows, or smart home panels.

* Electromagnetic Shielding Layers: Providing lightweight, transparent electromagnetic interference protection within flexible electronic devices.

Looking ahead, with advancements in nanomaterial dispersion technology and further improvements in the automation and intelligence of ultrasonic spraying equipment, this technology is expected to become the mainstream process in the manufacture of transparent conductive films. It will be more than just a deposition tool; it will be a comprehensive platform integrating material synthesis, structural control, and performance optimization, continuously driving innovation and transformation in next-generation optoelectronic devices.

About Cheersonic

Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.

Our coating solutions are environmentally-friendly, efficient and highly reliable, and enable dramatic reductions in overspray, savings in raw material, water and energy usage and provide improved process repeatability, transfer efficiency, high uniformity and reduced emissions.

Email: market2@cheersonic.com