Existing liquid crystal (LC) smart window technologies are yet to make inroads into the consumer market largely due to more than 50% of the cost-share by the tin-doped indium oxide...
Fabrication
protocols of transparent conducting electrodes (TCEs),
including those which produce TCEs of high values of figure of merit,
often fail to address issues of scalability, stability, and cost.
When it comes to working with high-temperature stable electrodes,
one is left with only one and that too, an expensive choice, namely,
fluorine-doped SnO2 (FTO). It is rather difficult to replace
FTO with a low-cost TCE due to stability issues. In the present work,
we have shown that an Al nanomesh fabricated employing the crack template
method exhibits extreme thermal stability in air even at 500 °C,
compared with that of FTO. In order to fill in the non-conducting
island regions present in between the mesh wires, a moderately conducting
material SnO2 layer was found adequate. The innovative
step employed in the present work relates to the SnO2 deposition
without damaging the underneath Al, which is a challenge in itself,
as the commonly used precursor, SnCl2 solution, is quite
corrosive toward Al. Optimization of spray coating of the precursor
while the Al mesh on a glass substrate held at an appropriate temperature
was the key to form a stable hybrid electrode. The resulting Al/SnO2 electrode exhibited an excellent transparency of ∼83%
at 550 nm and a low sheet resistance of 5.5 Ω/□. SnO2 coating additionally made the TCE scratch-proof and mechanically
stable, as the adhesion tape test showed only 8% change in sheet resistance
after 1000 cycles. Further, to give FTO-like surface finish, the SnO2 surface was fluorinated by treating with a Selectfluor solution.
As a result, the Al/F–SnO2 hybrid film exhibited
one order higher surface conductivity with negligible sensitivity
toward humidity and volatile organics, while becoming robust toward
neutral electrochemical environments. Finally, a custom-designed projection
lithography technique was used to pixelate the Al/SnO2 hybrid
film for optoelectronic device applications.
Fabrication of large‐area transparent conducting electrodes (TCEs) of high performance through cost‐effective high throughput methods has been an area of intensive research. In this context, the fabrication of flexible, 25 cm2 wide TCEs with high figure of merit (FoM) (≈494 Ω−1 ) is achieved by two roll‐to‐roll compatible processes, namely screen printing and spray coating, by suitably modifying crackle lithography in a cost‐effective manner. The fabricated TCEs exhibit low sheet resistance (<10 Ω □−1) and high transmittance (≈86–90%) in the visible region. The TCEs are shown to be highly bendable, the change in the sheet resistance is only ≈2% up on 6000 bending cycles. The application of these TCEs as transparent bendable uniform Joule heaters and surface capacitive touchscreens has also been demonstrated. The TCEs are, thus, just as good as any TCE produced using spin‐coating or similar small area coating techniques.
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