PhD Project by Eduard Llorens Balada

Project: Metal oxide thin films for optoelectronic applications
Group: Plasma Aided Nanotechnology
Supervisor: Eugen Stamate

Project description
Metal oxide thin films are widely used in optoelectronic applications, such as smart windows, displays, solar cells, thin film transistors (TFT), Internet of Things (IoT) and semiconductor devices. Among all the possible applications, we are interested in renewable energies and more precisely, in solar cells. Solar cells need to possess one transparent conductive layer that enables light to pass through while it works as a transparent front electrode.

As a front electrode material, different Transparent Conductive Oxides (TCO) can be used: Indium-doped Tin Oxide (ITO), Al-doped Zinc Oxide (AZO), and Gallium-doped Zinc Oxide (GZO). Although the material that offers the lowest conductivity is ITO, it is costly, therefore, a cheaper material that could offer the same benefits as ITO is wanted. One of the best candidates to replace ITO is AZO due to its low resistivity, high transmittance in the visible spectra, and low cost both for manufacturing and raw materials.

To fabricate metal oxide thin films, several techniques could be employed, nevertheless, magnetron sputtering is chosen as the manufacturing method since it can be used for large area applications due to its high deposition rate, good adhesion on substrates, film uniformity, and relative ease of controlling process parameters.

The main aim of this PhD project is to fabricate AZO thin films by means of magnetron sputtering, for a better growth mechanism understanding and to use them in solar cells applications.

Perspective
The main drawback to deposit a metal oxide layer using this method is the formation of oxygen negative ions within the plasma due to the high electronegativity of the oxygen and the presence of low-energy electrons either emitted from the target by secondary emission or produced by the plasma. These ions contribute significantly to the crystal quality, thickness, and composition uniformity; therefore, it is a must to study their influence on the growth mechanism to obtain the sought properties.

The hypothesis of this project is if we can tune the target-plasma-substrate sputtering system to obtain an AZO thin film layer that could replace ITO in optoelectronic devices.