Fabrication of a Highly Transparent Conductive Thin Filmfor Deicing and EMI Shielding Applications
Creators: name: Hosseini, Ehsan
Publisher: name: Graduate Studies
Year: 2020
Subjects: subject: Conductive Polymers
subject: Electromagnetic Shielding
subject: De-icing
subject: Transparent Thin Film
subject: Thin Film Heater Electrode
subject: Health And Environmental Sciences
subject: Energy
subject: Engineering--Chemical
subject: Chemistry--Polymer
subject: Chemistry--Organic
subject: Engineering--Materials Science

description: Transparent conducting films (TCFs) market has been continuously evolving and becoming available in a wide variety of applications, including touch screen panels, organic light-emitting diodes (OLEDs), photovoltaic solar cells, heaters and very recently, electromagnetic interference (EMI) shields. A majority of research and development (R&amp;D) on TCFs have been focused on materials that could replace the commonly-used indium tin oxide (ITO) – the substance that is not as favorable as before. Nevertheless, despite its drawbacks such as limited availability, brittleness, toxicity, and high cost, industry has not been persuaded to completely put an end to the ITO’s era. The underlying reasons for this include: (i) some of the proposed alternatives could not even reach the ITO’s unique properties of the optical transparency of &gt; 90% and sheet resistance of &lt; 10 ? sq–1, (ii) some reported materials excel only in one of the ITO’s property, either the transmission or sheet resistance, and (iii) new materials with similar or better properties than ITO, end up creating new challenges such as higher production cost, complex processing with more energy consumption, use of specialized, expensive methods, and the inferior mechanical stability of the end product. On the other hand, for transparent EMI shielding applications, in particular, metals as the most widely-used materials are not desirable anymore due to being corrosive, having low optical transmission and heavyweight. In this thesis, two novel fabrication techniques are introduced for making high performance (i) filler-free and (ii) hybrid TCFs. The ~ 50 nm filler-free highly conducting film is made of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), also known as PEDOT:PSS. To the best of our knowledge, it is the first all-plastic transparent EMI shield developed to date, which is only based on an intrinsically conductive polymer (ICP). The ultra-thin shield offered the total shielding effectiveness of 15 dB in the X-band frequency range (8.2–12.4 GHz) with an appreciable transparency of 97.1%. The shield also has a record thickness-specific shielding figure-of-merit of 300 dB µm–1 – far exceeding the best values for micron-thick metal-based, as well as carbon- and MXene-based composite materials shields. The other fabricated hybrid TCF, not only outperforms both the ITO and other reported TCFs to date but also circumvents the shortcomings of the previously-developed technologies and offers unprecedented new properties. The developed TCF presents the optical transparency of 91%, the sheet resistance as low as 6.4 ? sq–1 and the total EMI shielding of 23 dB in the X-band frequency range. The TCF owes its remarkable features partly to the outstanding qualities of its constituents: PEDOT:PSS, and silver nanowires (AgNWs), the most electrically-conductive material. The next critical part, contributing to the advanced attributes of the TCF, is its layer-by-layer (LBL) structure in which AgNWs are sandwiched in between PEDOT:PSS ultra-thin layers. Last but not least, the sandwich assembly of the TCF in between glass substrates in targeted applications such as deicing vehicles windshields and EMI shielding, makes the thin film electrode protected against harsh environmental conditions in winters, oxidation and scratches – a feature most current TCFs lack of. In addition to the two aforementioned significant applications, being identified and experimented, other functionality features of our fabricated TCF have been under ongoing research in collaboration with other groups, such as in biosensors and Li–S batteries applications, to name a few.