Transparent Conductive Material (TCM) films play a crucial role in energy and electronic domains since they are used in various devices such as for solar cells, organic light-emitting diodes, liquid crystal display panels or transparent heaters. In the field of photovoltaics, TCM thin films are used as front electrodes in solar cells and, therefore, should be as transparent and conductive as possible. Such TCM thin films have received increasing interest in recent decades thanks to their importance and the need to improve their properties. The most successful and commonly used TCM has been Indium Tin Oxide (ITO), but Indium is likely to become a commodity in short supply in the near future. Therefore research has been focused lately on Ag nanowire (AgNW) networks showing that AgNW networks are an extremely promising TCM [1].

However, despite considerable research efforts on AgNW networks, a better understanding of several problems is still required to better control and/or optimize their deposition, to shed light on the role of key parameters such as network density and silver nanowire morphology and that of post-treatment such as thermal annealing [2] on their physical properties. Furthermore, additional efforts should also be focused on more fundamental aspects. For instance, we need to understand the percolation mechanisms occurring in these networks, particularly in relation to the non-perfect networks associated with AgNW length distribution, non-isotropic orientations, nanowire curvature.

This PhD project will use a general approach, with the aim of contributing from both experimental and modelling aspects. For the simulation part, a range of algorithms have already been developed between the two partner laboratories during a previous thesis [1,2] and can serve as templates for new numerical calculations on non-ideal Ag NW networks for instance. Among important problems is the stability of such networks (either thermal, chemical or electrical) which should be thoroughly investigated experimentally. For instance, the nanowire network stability could be improved by an adequate coating by using a transparent semiconductor material such as ZnO or TiO2 which is expected to modify the work function.

Technological aspects will concern a better integration of AgNW networks as transparent electrodes in devices in close collaboration with the industrial partner Polymage. The applied domains will concern: solar cells, transparent heaters and electromagnetic devices (flexible and transparent antennas, electromagnetic shielding) for which one should take advantage of key features such as low fabrication cost, transparency, up-scaling and low-temperature methods (spray), and polymeric or glass substrates.

[1] “Flexible transparent conductive materials based on silver nanowire networks: a review”, D.P. Langley, G. Giusti, C. Mayousse, C. Celle, D. Bellet, J.-P. Simonato, Nanotechnology 24 (2013) 452001.
[2] “Metallic Nanowire Networks: Effects of Thermal Annealing on Electrical Resistance”, D.P. Langley, M. Lagrange, G. Giusti, C. Jimenez, Y. Bréchet, N.D. Nguyen, D. Bellet, Nanoscale 6 (2014) 13535.

Project Partners

Laboratoire des Matériaux et du Génie Physique, Grenoble INP, France: thin film synthesis with spray pyrolysis, spin-coating (and soon spatial atomic layer deposition); structural, electrical and optical characterization; physical modelling

Laboratoire de Physique des Solides, Interfaces et Nanostructures, Département de Physique, Liège University, Belgium: Admittance spectroscopy; Physical modelling

Industry Partner: Polymage, France: Integration of functional materials into devices within applications domains such as optics

Host Country (employment): France

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