ITO vs FTO Glass: Differences and How to Choose a Transparent Conductive Substrate

ITO vs FTO Glass: Differences and How to Choose a Transparent Conductive Substrate

Thin-film solar cells, OLEDs, electrochemical sensors and many spectroscopy experiments start with a piece of glass that conducts electricity yet lets light through. The two most common choices are ITO glass (indium tin oxide) and FTO glass (fluorine-doped tin oxide). They look alike, but picking the wrong one can leave you with an electrode that degrades during annealing or devices that are hard to reproduce.

This article compares ITO and FTO on resistance, smoothness, heat and chemical resistance and typical uses, and explains how to prepare the substrates before use.

The short version

  • ITO is tin-doped indium oxide. The coating is thin and very smooth, with high transparency in the visible range.
  • FTO is fluorine-doped tin oxide. The coating is thicker and rougher, but much more resistant to heat and chemicals.

Comparison based on product data

For reference, here are the specifications of Ossila substrates commonly used in research labs:

  • ITO glass: 100 nm ± 20 nm ITO on 1.1 mm polished soda lime glass. Quoted sheet resistance 20 Ω/sq, measured 14 – 20 Ω/sq with a four point probe. ITO surface roughness 1.8 nm RMS (AFM).
  • FTO glass: 200 – 300 nm FTO on 1.6 – 2.2 mm soda lime glass. Sheet resistance 6 – 9, 7 – 10 or 10 – 15 Ω/sq depending on grade; for the 7 – 10 Ω/sq grade, measured 7.49 ± 0.30 Ω/sq with 70% transmission from the front and 73% from the rear.

In these examples FTO has the lower sheet resistance but a rougher surface. ITO wins on smoothness, which matters for very thin active layers.

Heat resistance: the main reason to choose FTO

ITO can lose conductivity when heated strongly in air, so it is a poor fit for processes that need annealing at around 450 – 500 °C. FTO is stable at those temperatures. That is why FTO is the standard for stacks with sintered mesoporous or compact TiO2, such as dye-sensitized solar cells (DSSCs) and mesoporous n-i-p perovskite cells.

When to choose ITO, when to choose FTO

  • Choose ITO for OLEDs, OPV, planar and inverted (p-i-n) perovskite cells processed at moderate temperature, and experiments that need a very smooth surface such as STM and conductive AFM.
  • Choose FTO for DSSCs, mesoporous perovskite cells, photoelectrochemistry and water splitting, and any process involving high-temperature annealing or harsh chemicals.

Patterned or unpatterned

Patterned substrates come with electrodes already defined, so one substrate gives several pixels of known area. In the Ossila 20 x 15 mm system, for example, patterned FTO substrates give 8 pixels with the multi-electrode mask; in the 25 x 25 mm system, patterned ITO substrates hold four 48 mm² pixels or one large 255 mm² pixel. This saves etching time and makes batch-to-batch comparisons fairer.

Unpatterned substrates suit work that needs a continuous conductive layer (STM, conductive AFM, spectroscopy, electropolymerization, working electrodes) or your own patterning.

Preparing substrates before use

  1. Find the conductive side. Use a multimeter or a four point probe; the bare glass side does not conduct.
  2. Clean in stages. Sonicate in detergent solution, DI water, acetone and isopropanol, then dry with a nitrogen stream.
  3. UV ozone treatment. Removes organic residue and raises surface energy so solutions wet better during spin coating.
  4. Etch if needed. Unwanted areas of unpatterned substrates can be etched. FTO is more acid-resistant and needs a stronger etching treatment than ITO.
  5. Measure sheet resistance. Recording a baseline helps you spot electrode damage during processing.

ITO and FTO glass at AMI Scientific

Ossila ITO and FTO glass substrates, patterned and unpatterned in several sizes (usually packs of 100), plus deposition and aperture masks, are listed in our ITO, FTO Substrates & Masks collection. For the next steps, see spin coaters, the UV Ozone Cleaner, PEDOT:PSS and our guide to perovskite solar cell materials and equipment.

Tell us which devices you are making and the substrate size you need via WhatsApp and our team will help you choose and prepare a formal quotation for your institution.

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