18 May 2015 Congratulations to New ICFO PhD graduate

Dr. Nadia Formica


Thesis Committee

Dr. Nadia Formica graduated with a thesis in \'Mechanically Flexible Transparent Conductors based on Ultrathin Metallic Layers\' Dr. Nadia Formica received her Master Degree in Physics from the University of Catania, Italy, before joining the Optoelectronics research group led by ICREA Prof. at ICFO Valerio Pruneri. At ICFO, she centered her doctoral work on studying and understanding the properties of transparent conductors to improve their capacities for optoelectronic applications. Dr. Formica’s thesis, entitled ‘Mechanically Flexible Transparent Conductors based on Ultrathin Metallic Layers’, was co-supervised by Prof. Valerio Pruneri and Prof. Uli Lemmer.

Abstract

Transparent Conductors (TCs) are essential components in many applications, such as light emitting diodes, solar cells, rigid and tactile displays and smart windows, since they allow efficient light transmission while electric signals are applied or collected. To date, Indium doped Tin Oxide (ITO) exhibits the best trade-off between high optical transparency and low electrical resistance, making it the first choice as TC for the most optoelectronics applications. However, ITO has several important drawbacks such as high cost, poor mechanical flexibility and incompatibility with organic compounds, all of which prevent its use in future flexible and cost-effective high-performance devices.

A potential alternative avoiding these restrictions are Ultrathin Metal Films (UTMFs), thanks to their large mechanical flexibility, the possibility of low temperature-processing, and their low cost. Their low potential durability under oxidizing and corrosive conditions maybe a major concern for several applications. In this Thesis, various combinations of UTMFs have been investigated and optimized, to demonstrate that they can serve as an effective alternative to conventional ITO. Most importantly, several designs and methods have been developed for improving the stability of UTMFs, while at the same time still maintaining high optical and electrical characteristics. Aiming at flexible devices, the newly developed TC structures have also been deposited on flexible substrates, namely Polyetheylene therephtalate (PET) and the recently developed Corning Willow ultrathin glass, and their high transparency, electrical conductivity, and stability have been demonstrated.

Furthermore, to obtain improved UTMFs, the proposed UTMFs have been combined with several indium-free transparent conductive oxides, e.g. Aluminum doped Zinc Oxide (AZO). Also, two different approaches have been proposed to improve the stability of UTMFs and AZO layers at high temperature and in harsh ambient conditions. In first approach, an ultrathin oxidized Ti layer was found to greatly enhance the stability of AZO film without affecting the electro-optical properties. In a second approach, it was demonstrated that a single sheet of Graphene works as protection layer against degradation both for AZO and UTMFs. The search of proper barrier layers for TCs against oxygen and water vapour was thus addressed without compromising the mechanical flexibility, demonstrating the superior mechanical strength of UTMFs unlike the ITO. Finally, the Thesis demonstrates potential for technological applications by incorporating UTMF based TCs in organic solar cells with efficiencies comparable to those with state-of-the-art ITO. The research and results of the thesis open new routes for low cost and large scale manufacturing of flexible optoelectronic devices.


Thesis Committee

Prof. Arben Merkoçi
, ICN2- Universitat Autònoma de Barcelona
Prof. David Artigas, UPC-ICFO
Dr. Prantik Mazumder, Corning Inc., USA

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