Transparent conductive films are the ‘secret superpower’ of the smartglass sector. They enable the electrical connection of auto-tinting, privacy, or photovoltaic layers, while maximizing daylighting for sustainable green architecture.
C.Eng CITP LEED Green Associate
Last Updated on: 19th August 2026
When we look through a smart window and discover internal layers that conduct electricity, we might ask ourselves:
Where are the electrical conductors?
The answer lies in internal films of electrically-conductive materials which are transparent enough to transmit daylight.
The following diagram shows the typical structure of an auto-tinting smartglass panel with a switchable interlayer sandwiched between transparent conductive films.
The top and bottom layers of glass complete the laminated structure.
This format is typical of dye-doped liquid crystal, PDLC and SPD smart glass, but we can also find transparent conductors in electrochromic and transparent photovoltaic glass.
Transparent conductive thin films find uses not only as electrodes in smart glass and in photovoltaic solar panels, but also in the following applications:-
In this article, we learn why transparency and electrical conductivity are actually opposing trade-offs.
First, let’s look at the most prevalent transparent conductive material in use today, Indium Tin Oxide.
The most common transparent conductive material at the moment is Indium Tin Oxide (called ITO in the industry), a compound of indium oxide (which is transparent in thin films) and tin oxide, which increases the overall electrical conductivity of the material.
Currently, ITO offers the best combination of:
Typically, we deposit ITO on glass by either magnetron sputtering or pulsed-laser deposition (PLD).
Unfortunately, ITO suffers from volatile market price fluctuations due to its sparse distribution in the earth’s crust and is mechanically fragile, which makes it unsuitable for very large area displays.
Indium is not officially one of the 17 rare earth elements but is considered ‘rare’ due to its relative difficulty and cost of mining. Indium is in fact more abundant than silver, gold and platinum (but less abundant than copper or aluminium).
The current (March 2026) price of Indium is between USD 500-600 per kg which represents a 50% increase since Jan 2018 but a substantial drop since its peak price in 2014 (see the graph below).
Indium is mined across Japan, Canada, Peru and Mexico, with approximately 70% coming from China, and about 50% of all indium being refined globally for manufacture of ITO.
For many years now, the industry has been looking for alternatives to ITO, including both inorganic and organic materials. Below we can find some of the most promising technologies.
Inorganic:
Organic:
Fundamentally important to the functioning of any transparent conductive film is the bandgap, which is the ‘energy gap’ between:
The separation between the conduction and valence bands is the bandgap and represents the energy that electrons need to absorb from incoming light photons in order to ‘jump up’ to the conduction band and become ‘free electrons’.
For a material to be transparent, photons of light must not be absorbed or reflected but rather transmitted unimpeded through a material.
For this light transmission to happen, the energy of each photon must be less than the bandgap of that material, measured in electron-Volts (eV).
This means that the incoming photon will not have the energy needed to excite electrons from the valence band up to the conduction band. The photon therefore does not interact with free electrons and is not reflected or absorbed.
It is transmitted.
And since visible light has wavelengths of 380 nm to 760 nm, this corresponds to photon energies of 1.6 eV to 3.2 eV.
Therefore, the bandgap (in the visible region) must be greater than 3.2 eV in order for the material to transmit photons of visible light.
ITO has a bandgap of 4.0 eV which explains why it is transparent to visible light.
This does not yet explain why ITO reflects infrared, when infrared photons have less energy than visible light. Surely the same applies to infrared photons?
The explanation is simple:
ITO actually reflects infrared due to the (small amount of) ‘free electrons’ already present in the material (thanks to the tin oxide), which oscillate in response to the incident infrared waves, leading to absorption and reflection of infrared only (but not visible light).
Net result:
ITO transmits visible daylight into a building beautifully, but rejects the solar heat that can cause overheating and excessive air conditioning costs.
How cool is that?
Furthermore, researchers can engineer a variety of optical properties (e.g. transmittance, heat rejection, haze), based on the requirements of each application.
This results in products that companies can ‘fine-tune’ according to individual market needs by altering the proportions of the constituent elements
So, we see that transparency and conductivity are actually at odds, since transparency to visible light requires a large bandgap but conductors imply a small bandgap.
ITO does both, by having a large bandgap in the visible range but (thanks to the tin oxide) having a higher electrical conductivity than the indium oxide alone, turning the material from an insulator to a semiconductor.
Just as an aside, metals have no bandgap (their valence and conduction bands actually overlap), allowing for their high conductivity.
ITO is not a metal, but a metal oxide (classified as a semiconductor), having an electrical conductivity between that of metals and insulators.
In fact transparent conductive films in general occupy a strange niche, seemingly giving them ‘superpowers’, without which smartglass would simply not exist.
The smartglass industry is heavily invested in Indium Tin Oxide at the moment but research is advancing in alternatives that exhibit better light transmittance, electrical conductivity and mechanical stability.
We should remember that any transparent conductive layer represents only a small section of the overall smartglass stack. Even drastic improvements may be thwarted by the limitations of the other material layers present in the stack.
Having said that, it is unlikely that indium tin oxide will be completely replaced any time soon. Despite the volatile market prices, indium may still be a pretty good commodity to invest in for the time being.
C.Eng CITP LEED Green Associate
Manoj’s first experience with glass was in 1990 fabricating optical waveguides as a student engineer sponsored by Ferranti Semiconductors. After two decades working on hardware-software projects across telecom and automotive sectors, Manoj founded ArtRatio, a manufacturer of smart glass display cases, with clients such as the National Museum of Sweden and Harvard University. Manoj is a UK Chartered Engineer with degrees in Software & Electronics Engineering from Oxford and Southampton Universities, and holds a European patent for the sustainable display of art & luxury collections using smart glass. Through Smartglass World, Manoj now offers consultancy to ESG investors, property developers, architects, facade engineers and OEM manufacturers.
