METAL NANOWIRE NETWORKS AS TRANSPARENT CONTACTS
Husnu Emrah Unalan
1,2,3
1
Micro and Nanotechnology Department, METU, Ankara 06800, Turkey
2
Center for Solar Energy Research and Applications (GUNAM), METU, Ankara 06800,
Turkey
3
Department of Metallurgical and Materials Engineering, METU, Ankara 06800, Turkey
E-mail:
Figure of merit transparency and sheet resistance values of the metal nanowire networks are
very close, if not better, than those of commercially available transparent and conducting thin
films. In addition, nanowire networks carry the prominent advantage of solution
processability and flexibility. In this presentation, our efforts on the utilization of silver (Ag)
and copper (Cu) nanowire networks as transparent contacts for polymeric light emitting
diodes, solar cells, transparent heaters and supercapacitors will be presented. Following their
synthesis and purification, nanowires are deposited onto various substrates in the form of
networks through spray coating. Surface roughness and long-term stability of the networks
are carefully monitored, where the latter is a particularly important problem for Cu
nanowires. Infiltration of a conducting polymer decreased the roughness associated with the
networks so that they can be used as anodes in polymeric light emitting diodes. When used as
transparent heaters, reproducible heating characteristics and uniform temperature distribution
are obtained from the networks. The effect of nanowire density on the temperature profile,
applied voltage, contact geometry, incremental bias application as well as turn on/off
characteristics are investigated. Ag NW network based transparent heaters with a sheet
resistance, percent transmittance of 4.3 Ω/sq and 83.3% with a nanowire density of 1.6
NW/μm
2
reached to a maximum temperature of 275°C under incremental bias application up
to 5V. The demonstration of metal nanowire networks in
supercapacitors is very limited.
With this motivation,
nanocomposite electrochromic supercapacitor electrodes with silver
nanowire network electrodes and a novel conducting polymer are fabricated. High
transparency and conductivity of the silver nanowire network contacts allowed the fabrication
of electrochromic supercapacitors and investigation of the spectroelectrochemical and
electrochemical properties of the conducting polymer. Specific capacitance of the fabricated
nanocomposite electrodes is calculated as 61.5 F g
-1
and noticeable capacity retention is
obtained upon 20000 galvanostatic charge-discharge cycles. Investigated electrochromic
supercapacitors changed their colors from green to transparent, which might be used to
communicate with the users in smart electronic devices.
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