Alternative materials for flexible transparent conductive electrodes

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Lordan, Daniel
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University College Cork
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This thesis investigates new alternative materials for flexible transparent electrodes: monolayer graphene and micron-scale metal mesh structures. Growth of graphene on copper foils by chemical vapour deposition (CVD) was investigated by commissioning and developing a CVD system in Tyndall. Initial growth runs resulted in poor graphene coverage. Several routes for growth improvement were examined: an acid pre-treatment, substrate geometry and growth pressure. Following this improvement, a continuous growth run was carried out displaying high monolayer graphene coverage. Graphene was transferred to Si/SiO2 (90 nm thermal oxide) and glass substrates using a wet chemical transfer process. This process involves the use of a polymer which acts as a support mechanism. However, polymer residue can have drastic effects on the electrical performance of CVD graphene films. Therefore an alternative method for polymer removal with the use of heated acetone (~ 60 oC) was investigated. Micron-scale platinum mesh structures were fabricated on rigid glass substrates using a range of metal deposition techniques; metal evaporation and lift-off; ALD and dry etching and sputter deposition and dry etching. Square, hexagonal, circular and a new asymmetric pentagonal tiling were utilised as metal meshes. Their performance were investigated along with the metal deposition technique. Evaporation and lift-off provided the most consistent technique in relation to transparency, haze and sheet resistance. Finally, asymmetric pentagonal platinum meshes were fabricated on flexible transparent substrates using metal evaporation and lift-off. All designs were bent around a radius of curvature (in air) of ~ 3.8 mm up to 1,000 bending cycles for both tension and compression and suggested good performance in comparison to literature. All three designs were used as transparent heaters via Joule heating. All heaters demonstrated good thermal characteristics such as low response times and high thermal resistances. Finally, a pentagonal metal mesh was used to de-ice a glass substrate.
Metal meshes , Transparent electrode , Flexible , Graphene transfer , CVD Graphene , Graphene , Pentagon , Asymmetric , Transparent heaters , Polyethylene terephthalate , Sputtering , Evaporation , Chemical vapour deposition , Atomic layer deposition
Lordan, D. 2017. Alternative materials for flexible transparent conductive electrodes. PhD Thesis, University College Cork.