Some typical transparent conductive films (TCFs) are ITO, AZO, and CNT. They have advantages in transparency and conductivity. The combination of the two properties make TCFs important. Therefore, they are widely used in the electronic equipment industry as electrodes on light emitting diodes (as shown in Figure 3.1) and photovoltaic devices. For instance, TCFs can be made into transparent electrodes to detect touch and quickly switch colours, and this product can be used on smartphone touch screens and flat panel televisions [11].

Figure 3.1. A flexible device with a transparent electrode [12].

ITO is an important type of TCFs. It contributes to both research and industry. Most of today’s transparent electrodes are made of ITO due to its high transparency [11]. And transparent means that when it appears on the glass screen, it is invisible. Conductivity is the reason why the touch screen can work. ITO performs better in transparency, conductivity, high temperature resistance than similar conductive materials (e.g. fluorine-doped tin oxide) [20]. The material can be applied in many fields such as smart window, thin film photovoltaics, optical coatings, and so on. By applying a voltage to the film, it can produce heat, hence, ITO film can be used to defrost aircraft windshields (as shown in Figure 3.2).

Figure 3.2. Thin film interference caused by ITO coating on the window [13].

Aluminium doped zinc oxide (AZO) thin films are attracting more and more attention on the application in thin film devices as an alternative to ITO. Compared with ITO, AZO is less expensive, and this is one of the reasons that AZO can replace ITO. Besides that, AZO has advantages in non-toxic, resource availability and stability. They are widely applied because of their good electrical and optical properties. AZO is usually doped with some metal elements, for example, Al doped ZnO have higher transparency and lower resistivity [19], and these characteristics make AZO perform better in various specific applications. Some applications of AZO are solar cells, gas sensor, thin film transistors and so on [14]. As shown in Figure 3.3, AZO is often used as a coating material.

Figure 3.3. AZO coated glass slides [15].

Thin films composed of carbon nanotubes (CNTs) are new alternative to ITO films. Compared with other alternatives, CNT exhibit high electrical conductivity and high optical transparency. More importantly, CNT provides easier manufacture process and more stretchable and flexible platform with stronger mechanical strength [21]. A typical example of CNT-based TCFs is organic light emitting diode device.

Nowadays, transparent conductive films begin to swing into success territory. More opportunities are opening up for ITO and its alternatives. The efficiency of manufacturing and the quality of TCFs will be developed further. It is predicted that the total market for transparent conducting layer (glass and film) will double by 2028 compared to its 2017 value [16]. In conclusion, due to the excellent properties in optical and electrical, TCFs will have a promising future in many fields.

References

[11] Transparent, conductive films promising for developing flexible screens. (2020). Retrieved 7 June 2020, from https://phys.org/news/2018-06-transparent-flexible-screens.html

[12] A flexible device with a transparent electrode. (2020). [Image]. Retrieved from https://www.spiedigitallibrary.org/ContentImages/Journals/JPEOBV/4/1/040990/WebImages/JPE_4_1_040990_f005.png

[13] Transparent, conductive films promising for developing flexible screens. (2020). Retrieved 7 June 2020, from https://phys.org/news/2018-06-transparent-flexible-screens.html

[14] A flexible device with a transparent electrode. (2020). [Image]. Retrieved from https://www.spiedigitallibrary.org/ContentImages/Journals/JPEOBV/4/1/040990/WebImages/JPE_4_1_040990_f005.png

[15] Etan J. Tal. (2013). Thin film interference caused by ITO coating on the window [Image]. Retrieved from https://www.aps.org/publications/capitolhillquarterly/201607/thin-films.cfm

[16] Subramanyam, T. (2018). Optimization of Sputtered AZO Thin Films for Device Application. Elsevier. Retrieved from https://doi.org/10.1016/j.matpr.2017.12.373

[17] Techinstro. (2020). AZO coated glass slides [Image]. Retrieved from https://www.amazon.ae/Techinstro-Aluminium-coated-slides-Resistivity/dp/B07WW19VX6?th=1

[18] Ghaffarzadeh, D. (2020). Transparent conductive films and materials: past, present and future. Retrieved 7 June 2020, from https://www.idtechex.com/en/research-article/transparent-conductive-films-and-materials-past-present-and-future/14052

[19] Sukee, A., Kantarak, E., & Singjai, P. (2017). Preparation of Aluminum doped Zinc Oxide Thin Films on Glass Substrate by Sparking Process and Their Optical and Electrical Properties. Retrieved from https://iopscience.iop.org/article/10.1088/1742-6596/901/1/012153/pdf

[20] Difference between ITO and FTO coated glass. (2020). Retrieved from https://www.techinstro.com/difference-ito-fto-coated-glass/

[21] Carbon nanotube based transparent conductive films: progress, challenges, and perspectives. (2020). Retrieved 9 June 2020, from https://www.tandfonline.com/doi/full/10.1080/14686996.2016.1214526#:~:text=One%20of%20the%20most%20promising,which%20use%20indium%20tin%20oxide.&text=The%20challenges%20of%20current%20CNT,with%20other%20TCFs%2C%20are%20considered.