Abstract
Conductive nano-composites have the potential to replace traditional conductive materials due to the enhanced mechanical, electrical and chemical properties that lend themselves to a plethora of applications. In this work, conductive nano-composites of poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate) with multi-walled carbon nanotubes (PEDOT:PSS/MWCNT) and PEDOT:PSS with silver nanowires (PEDOT:PSS/Ag NW) were prepared, characterized and tested for gas sensing and lighting applications. Carbon nanotubes were functionalized covalently with carboxylic acid and non-covalently with surfactant and polymer molecules. The functionalized nanotubes were mixed with PEDOT:PSS at different concentrations and printed using inkjet printing techniques. The effect of the concentration of these nanotubes on the electrical properties of the nano-composite samples was investigated. The results show that the electrical conductivity of the printed structures strongly depends on the concentration of the nanotubes in the sample. Furthermore, the electrical properties strongly depend on the wetting of the substrate and by controlling the wettability, the conductivity of the nanocomposite samples can be improved. Based on polymer conductivity, the electrical conductivity of the composite film can be improved or degraded by orders of magnitude with the incorporation of the MWCNT. Moreover, electrical measurements show strong correlation between the conductivity of the carbon nanotube network and the resulting nano-composite films. Excellent alignment of the nanotubes with improvement in the conductivity of the printed sample was also achieved using a novel and simple methodology. Carbon nanotube gas sensors were fully printed on flexible substrates and tested as ethanol sensors. The performance shows significant enhancement in the sensitivity of the PEDOT:PSS/MWCNT based sensor, in comparison to the pristine nanotubes and pristine polymer based sensors with enhancement factor greater than 2. 5. Moreover, a remarkable improvement in the response and recovery time of the sensor after polymer functionalization is also reported. Silver nanowires with a high aspect ratio and high conductivity were synthesised via polyol reduction of silver nitrate in the presence of metal salt and a capping agent. Conductive PEDOT:PSS/Ag NW composites were prepared using film transfer techniques and spray/inkjet printing techniques. The SEM images show excellent percolated networks of nanowires in the samples. The influence of thermal treatment on the electrical properties of the nanowire samples was investigated and found to improve the electrical conductivity. Moreover, the results revealed that the properties of the nano-composite films depend on the density of the nanowires in the samples. High conductivity with good optical transparency was achieved by controlling the concentration of the nanowires in the films. The Ag NW based samples exhibit high figure of merit values higher than those reported for graphene and carbon nanotubes based films, and better than industrial requirements for transparent conductor electrodes. The highly conductive and transparent PEDOT:PSS/Ag NW electrode was utilized to fabricate organic light emitting diodes. The device exhibited good performance with maximum luminance of about 2000 (cd/m2). The results show that the combination of the nano-composite materials together with the solution based technique could pave the way towards flexible, solution processable, low cost and large area device applications.