Transparent conductive film is a kind of basic photoelectric material with high conductivity and high transparency in visible light band.[1]There are four kinds of transparent conductive film : ITO(1960s) , FTO, AZO(1980s) and CNT(1991s).

ITO films, types of transparent films Geomatec began technological development of in the 1970s. These transparent-yet-conductive thin films are now crucial components of the high-resolution liquid crystal displays and touch sensor functions in the smartphones people use in their daily lives. ITO stands for Indium Tin Oxide. ITO - an inorganic mixture of indium(III) oxide (In2O3) and tin(IV) oxide (SnO2)-ranges from yellow to gray in powder form, but is transparent and colorless as a thin film. This makes it widely useful as a transparent-yet-conductive thin film.[2]

Aluminum-doped ZnO (AZO) has huge prospects in the field of conductive electrodes, due to its low price, high transparency, and pro-environment. However, enhancing the conductivity of AZO and realizing ohmic contact between the semiconductor and AZO source/drain (S/D) electrodes without thermal annealing remains a challenge.[3]

Carbon nanotubes (CNTs) have received increasing attention due to their outstanding mechanical, thermal, and electrical properties. In particular, research has focused on realizing in macroscopic objects the properties of single CNT molecules. CNTs have been formed into neat fibers as well as thin conductive films. In particular, transparent CNT films could replace indium tin oxide (ITO) because of their flexibility, resistance to flexural fatigue, and ease of manufacturing compared to the brittle ITO films, which must be fabricated by sputtering at low pressure or chemical vapor deposition at high temperature. Moreover, CNT films may enable new applications in flexible electronics, because of their ability to bend repeatedly without cracking.[4]

There are only ITO and FTO transparent conductive films which have been commercialized on a large scale. The transparent conductive films with the best comprehensive properties occupy about market share 94% .[1]

There are many preparation methods of ITO, including physical vapor deposition (PVD) includes vacuum thermal evaporation, electron beam thermal evaporation, magnetic controlled splash. Laser, ion beam sputtering, spraying, pulsed laser deposition (PLD) and so on. Chemical vapor deposition (CVD) includes molecular beam epitaxy. Atomic layer epitaxy, ion implantation, spray pyrolysis, sol gel Method, PECVD, etc.[1]

At present, the commercialized products of transparent conductive films are single, only ITO and FTO, which can not meet the market demand; the research of ITO alternative materials is under way, and there is no practical alternative materials.[1]

There are three main research directions in the future

(1) preparation of new transparent and conductive thin films to meet the needs of flat panel display devices, thin film solar cells, touch screens and other photoelectric devices, including the improvement of work function, surface roughness, environmental stability and other performance.

(2) starting from the materials, we should develop transparent conductive oxide films without indium or with less indium to reduce the dependence of the films on the metal indium.

(3) starting from the preparation technology, the wet deposition technology which can be prepared in the atmosphere and low temperature is developed in order to form a large area of film and reduce the cost of film preparation.[1]

Transparent conductive film has a wide range of applications. Transparent conductive film is mainly used as window material for photoelectric devices (such as LED, thin film solar cell). Transparent conductive films are also part of many devices, including electrochromic glass, solar panels, LCD and OLED displays. The common transparent conductive films are ITO (tin doped indium trioxide), AZO(aluminum doped zinc oxide), etc. They have a wide band gap and only absorb ultraviolet light, not visible light, so they are called "transparent". It can also be used in touch screens and solar panel.[5]

Transparent conductive film is the key electrode material for optoelectronic devices, not only now, but also in the future in the plane display, touch screen, film solar cell and other fields have a huge market demand.

[1]Liao Yaqin, Status and Development Tendency of Transparent conductive film, Dongfang Electric Review, 03/25/2014, Volume 28, 13-18

[2]Our ITO & Transparent Conductive Films, https://www.geomatec.com/products-and-solutions/electricity-control/our-ito-and-transparent-conductive-films/.

[3]Highly Conductive and Transparent AZO Films Fabricated by PLD as Source/Drain Electrodes for TFTs, Hongke Zhang,1 Xiaoqing Li,1 Zhiqiang Fang,2 Rihui Yao,1,* Xiaochen Zhang,1 Yuxi Deng,1 Xubing Lu,3 Hong Tao,4 Honglong Ning,1,* and Junbiao Peng1, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6317027/.

[4]High-Performance Carbon Nanotube Transparent Conductive Films by Scalable Dip Coating, Francesca Mirri, Anson W. K. Ma, Tienyi T. Hsu, Natnael Behabtu, Shannon L. Eichmann, Colin C. Young, Dmitri E. Tsentalovich, Matteo Pasquali, ACS Nano 2012, 6, 11, 9737–9744, Publication Date:October 6, 2012，https://doi.org/10.1021/nn303201g.

[5]"NBC Flex- The Transparent Film Transforms Any Surface Into Flexible 3D Touchscreen". Technocrazed.Com, 2020, http://www.technocrazed.com/stretchable-film-can-make-touchscreen-any-surface.

[6] S. Taylor， S. McLennan. The geochemical evolution of the continental crust［J］. Ｒeviews of Geophysics，1995，33( 2) : 241 －265

[7]Jonathan K. Wassei，Ｒichard B. Kaner et al . Graphene，a promising transparent conductor［J］. Materials Today，2010，13 ( 3) : 52－59

[8]Cui， JiWang， Anchuan， Edleman et al. Indium Tin Oxide Alternatives—High Work Function Transparent Conducting Oxides as Anodes for Organic Light ‐ Emitting Diodes［J］. Advanced materials，2001，13( 19) : 1476－1480

[9]Eda，Goki Fanchini，Giovanni Chhowalla，Manish et al. Large-area ultrathin films of reduced graphene oxide as a transparent and flexible electronic material［J］. Nature nanotechnology，2008，3 ( 5) : 270－274

[10]http: / /www. displaysearch. com. cn /press _ releases/20130827 － QMPD. php