Formation of a conductive overcoating layer based on hybrid composites to improve the stability of flexible transparent conductive films

Abstract

A protective layer that can be applied on a flat flexible transparent conductive film was prepared by combining silica sol and organic polymer. (3-Glycidyloxypropyl)trimethoxysilane (GPTMS) was used as a precursor for the silica sol, which hydrolyzed under moisture to form silanol groups and selfcondensed to form a sol under acidic conditions. Therefore, the organic polymer used was poly(4styrenesulfonic acid) (PSSA), which is acidic and water-soluble; thus, the silica precursor can form a sol and can cause chemical condensation with the silica sol under thermal conditions. However, as this protective layer was insulating, there was difficulty in conducting electricity to the lower portion through the upper contact. Therefore, a small amount of conductive polymer, poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), was added to the protective layer to make the overcoating layer itself conductive, thereby enabling electrical conduction to the underlying conductive film. The network structure of the overcoating layer surface could block oxygen and moisture, thus improving chemical stability. Therefore, under high-temperature and high-humidity conditions for 500 h, the sheet resistance increased by 145% before overcoating but increased by 33% after the overcoating layer was formed with appropriate thickness. In addition, the bonding strength of the surface was further improved. Peel-off occurred after applying a pencil having hardness of 5B or more before the overcoating treatment; however, after the overcoating treatment, no damage was caused by a pencil having hardness of 5H or less. Consequently, the overcoated conductive film maintained flexibility and transparency; it also exhibited desirable electrical characteristics, improved chemical stability, and excellent scratch resistance.

Effects of Cationic Species in Salts on the Electrical Conductivity of Doped PEDOT:PSS Films

“…As shown in Figure 2d, the broad absorption band near 850 nm is attributed to oxidation state of PEDOT, i.e., the single polaron with a positive charge. [42][43][44] By referring to this peak, we found that PEDOT:PSS/salts films showed a much stronger absorption than PEDOT:PSS, corresponding to an enhanced oxidation level (i.e., higher p-doping density) of PEDOT chains. 29 The PEDOT conductivity is primarily dependent on the positive charges located along the polymer backbone.…”

Synthesis of Stretchable, Environmentally Stable, Conducting Polymer PEDOT Using a Modified Acid Template Random Copolymer

“…With PEGMA as an additive, PEDOT:PSS has flexible properties even after 400% elongation and does not lose the electrical conductivity. However, this electrical conductivity does not last long under ambient conditions because it does not have sufficient environmental stability 31. In the case of PEDOT:P(SS‐ co ‐PEGMA), the relatively hydrophobic PEGMA component is fixed in the P(SS‐ co ‐PEGMA) chain; hence, the polymer is more stable than with PEGMA as an mere additive, as per contact angle analysis (Section S5, Supporting Information).…”

Revealing the improved sensitivity of PEDOT:PSS/PVA thin films through secondary doping and their strain sensors application

“…As far as we have a concern, there is no complete and sufficient mechanism explained on the crystallinity, stretchability and conductivity effects upon secondary doping of PEDOT:PSS. [19][20][21][22] To date, it is still a challenge to fabricate polymer-based strain sensors with desired mechanical properties and sensing performance by intoxicated materials and facile preparation methods.…”