Laser processing of transparent conducting films for use in flexible electronics

Eden, Jack

Abstract

Transparent conducting films based on novel materials have been laser processed on glass and flexible polyethylene terephthalate (PET) substrates in order to increase their electrical conductivity. The goal was to reduce the amount of indium used in display and photovoltaic applications by printing the indium containing compounds, hence only depositing material where it is required, or by using non indium-based materials. Two systems were considered: an ink containing indium tin oxide (ITO) nano particles with a polymer binder and organic solvent, and an ink containing aluminium doped zinc oxide (AZO) nanoparticles in a titanium dioxide solution.

The conductivity of the as-deposited material was thought to have been improved in two ways: UV-induced photopolymerization of binder material and the removal of non conductive material from within the inks. The first shrinks the polymer binder bringing the conductive particles closer together and the second decomposes or vapourizes the organic components. Consequently, laser sources covering the UV and the infrared were used. These were the argon fluoride, xenon chloride, and helium cadmium lasers (193nm, 308nm, and 325nm wavelengths respectively) and the Yb:YAG and CO₂ lasers (1030nm and 10.6μm wavelengths respectively).

Thermal measurements confirmed low temperature processing in the UV and each of the ultraviolet lasers increased the electrical conductivity of the films by at least 3 orders of magnitude. The XeCl laser gave the best result of ~1.5kΩ/sq. Higher temperature processing with the CO₂ laser gave~250Ω/sq but substrate damage occurred on temperature sensitive substrates. The current state of the art ITO films used in commercial devices are ~10Ω/sq. Absorption spectra were used to not only obtain evidence that polymerisation was occurring (even with the IR laser) but also to quantify the charge carrier density and band gap.

The intrinsic conductivity of the AZO compounds was found to be very poor and so fine silver grids were manufactured by laser ablation to provide additional current pathways. Carbon dioxide laser irradiation of the AZO films gave a lowest sheet resistance of 2.3MΩ/sq whereas the use of an underlying silver grid resulted in 3Ω/sq.

Citation

Eden, J. Laser processing of transparent conducting films for use in flexible electronics. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4222279

• Thesis Type: Thesis
• Deposit Date: Mar 9, 2020
• Publicly Available Date: Feb 23, 2023
• Keywords: Physics
• Public URL: https://hull-repository.worktribe.com/output/4222279
• Additional Information: Department of Physics and Mathematics, The University of Hull
• Award Date: Feb 1, 2020