The principle of anti-reflective conductive film (AR conductive film)
When light enters an uncoated glass substrate from the air, each interface reflects about 4% of the light, resulting in only 92% of the light passing through. Coating an anti-reflective film can make the light 180° out of phase at the upper and lower boundaries of the film, that is, the reflected light beam undergoes destructive interference, thereby achieving the anti-reflective effect while maintaining good light transmittance.
When light enters an uncoated glass substrate from the air, about 4% of the light is reflected at each interface, resulting in only 92% of the light passing through. Coating an anti-reflective film can make the phase difference of light at the upper and lower boundaries of the film 180°, that is, the reflected light beam undergoes destructive interference, thereby achieving the anti-reflective effect (as shown in Figure 1), and at the same time has good light transmittance .
Conductive films have a wide range of applications. In addition to general conductivity, they can be used as heating films, antistatic films, or even electromagnetic shielding films. However, in the optical fields such as displays, smart glass, or lenses, the use of metal conductive films will affect optical specifications. Therefore, considering price and effect, transparent conductive oxide (TCO) is a better choice. As for why TCO has the two properties of "transparency" and "conductivity", the reason why metals conduct electricity is because the conduction band and valence band overlap in the energy band[2], so electrons can move freely (as shown in Figure 2), which means there is no band gap, that is, it cannot transmit light. The band gap of TCO is about 2~4.5eV. When energy is applied to the transparent conductive film from the outside, electrons can be easily excited from the valence band to the conduction band. The existence of the band gap means that the material is likely to be transparent. Therefore, transparent conductive films can transmit light in the visible light (VIS) and near-infrared (NIR) bands and have a certain conductivity.
TCO is defined as having a light transmittance of over 80% and a resistivity of less than 1×10-3Ω-cm in the visible light wavelength range (400~700nm). The transmittance and conductivity of TCO are slightly inversely proportional, meaning that the higher the transmittance of the thin film, the worse the conductivity . Moreover, TCO is usually a high refractive index material. If TCO is deposited on glass, about 9.6% reflection will occur at a single interface. Therefore, it is a major challenge to apply TCO to high-end optical products.
Through optical multilayer film simulation and design, different materials are stacked to cause destructive interference of reflected light, thus achieving both anti-reflection and conductive film performance.
Applications of Anti-reflective conductive film (AR conductive film)
The excellent optical and electrical properties of AR conductive films allow them to be used as transparent heaters, quickly and effectively heating glass and plastic components (such as windshields or lampshades) in outdoor surveillance lenses, automobiles, or other vehicles, providing them with defogging and/or de-icing functions in harsh environments to maintain component performance.
