FTO Darkening Rate as a Qualitative, High-Throughput Mapping Method for Screening Li-Ionic Conduction in Thin Solid Electrolytes

Shay Tirosh, Niv Aloni, Simcha Meir, Arie Zaban, David Cahen, Diana Golodnitsky

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


We present a high-throughput (combinatorial) method to screen thin ceramic films as Li-ion conductors by mapping an optical effect of Li-ion conduction. The method, while qualitative, is fast and simple to implement, provides a planar (XY) map of Li-ion conductivity through different parts of the film. The effect, FTO darkening, is an optoelectrochemical one that relies on darkening of the FTO (F-doped tin oxide) substrate, onto which the investigated film is deposited. The rate of color change of the FTO reflects the rate of Li-ion migration through the film. The method is validated by testing two model systems, a Li-La-S-O film with uniform composition and varying thickness, and a Li-La-P-O film with varying thickness and lateral composition. The darkening rate, obtained from optical transmission, correlates linearly with inverse film thickness. The darkening rate map can be compared with a resistance map obtained by impedance measurements, showing that only Li conduction is measured. We discuss the conditions required to distinguish between areas with pure ion conductivity and those with mixed conductivity, the reversibility of the darkening effect and artifacts.

Original languageEnglish
Pages (from-to)18-24
Number of pages7
JournalACS Combinatorial Science
Issue number1
StatePublished - 13 Jan 2020

Bibliographical note

Funding Information:
We thank Eli Rosh Hodesh for technical assistance, Adi Kama, and Anat Izhak for analytical assistance and fruitful discussions. We acknowledge partial support of the Prime Minister’s Fuel-Choice Initiative, within the framework of the “ Israel National Research Center for Electrochemical Propulsion ” (INREP), funded by the Planning & Budgeting Committee of the Israel Council for Higher Education (CHE), and from the Israeli Ministry of Science and Technology (grant 53886).

Publisher Copyright:
© 2019 American Chemical Society.


  • FTO darkening rate
  • combinatorial science
  • high-throughput
  • impedance of thin film electrolytes
  • optoelectrochemical
  • qualitative screening
  • thin-film solid electrolyte


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