Facile and Customizable Selective Patterning of Silver Nanowires Via Solution Process for Stretchable Electrodes
Authors: Shim Jinbo , Yoon Jinsu , Dahyun Kim , Park Jong Ho , Jeong Yeeun , Hong Yongtaek 
Published: December 2024

In stretchable electronics such as wearable devices or electronic skin (E-skin) [1], silver nanowires (AgNWs) have been receiving significant attention owing to their compatibility with solution-based processes, high electrical conductivity, and excellent optoelectronic properties, all while exhibiting superior mechanical flexibility. [2]
Many researches of patterning methods have been studied to achieve AgNW patterns including photolithography [3], laser ablation [4], stamp contact printing [5], and spray coating [6]. However, these methods have encountered high-costs, damages to substrate, and limits toward large-area mass production. Furthermore, challenges remain in the patterning of AgNWs, such as process complexity and limited design freedom.
In this study, we introduce a straightforward and adaptable method for mask-less selectively patterning AgNWs, employing a drop-on-demand inkjet printing or dispensing process with the elastomer poly(vinylidene fluoride-co-hexafluoropropylene) (e-PVDF-HFP) to achieve facile and customizable electrode designs. When AgNWs are dispersed on stretchable substrates such as polydimethylsiloxane (PDMS), they are anchored on the elastomer e-PVDF-HFP. Utilizing this property, we have developed a selective patterning method to fabricate AgNW electrodes where AgNWs are confined only to the e-PVDF-HFP layer on the top of PDMS substrate. Additionally, e-PVDF-HFP ensures compatibility with a variety of stretchable electronic applications due to its excellent flexibility.
Fig. 1 shows the schematic of selective patterning of AgNW using e-PVDF-HFP. First, e-PVDF-HFP is inkjet-printed or dispensed onto a surface-treated carrier substrate to form the desired pattern. PDMS is then poured over the patterned e-PVDF-HFP and cured to embed the patterned e-PVDF-HFP into the PDMS. Once the PDMS is separated from the carrier substrate, the printed e-PVDF-HFP pattern appears on the surface of the PDMS substrate and the PDMS occupies the remaining area. Subsequently, AgNW is spray-coated on the PDMS substrate. During the sonication of the IPA solution, the e-PVDF-HFP maintains the AgNW to form an electrical path while the AgNW on the PDMS surface is removed.
We have studied that achieving an appropriate balance of wetting properties is needed to achieve optimal results in pattern formation on a carrier substrate and embedding into PDMS. The wetting properties of e-PVDF-HFP have a significant influence not only on the pattern morphology but also on the adhesion and embedding between e-PVDF-HFP and PDMS. Therefore, it is important for the material to exhibit favorable wetting properties in order to successfully form e-PVDF-HFP patterns on carrier substrates. In addition, embedding e-PVDF-HFP in PDMS requires optimizing the adhesion balance through surface treatments. This balance must be maintained between the carrier substrate – e-PVDF-HFP, and PDMS – e-PVDF-HFP. For instance, it is crucial for e-PVDF-HFP to have stronger adhesion to PDMS than to the carrier substrate for embedding e-PVDF-HFP into PDMS.
In the results, solution-processed e-PVDF-HFP on the carrier glass (Fig. 2. (a)) was effectively embedded into the PDMS substrate as shown in Fig. 2. (b). We note that 0.01wt% red dye was added to better identify the e-PVDF-HFP patterns. Next, AgNWs were deposited onto the patterned e-PVDF-HFP embedded within the PDMS and then ultrasonicated. Finally, selective patterning of AgNWs is achieved only in the e-PVDF-HFP region, and the AgNWs on the PDMS substrate are removed as shown in Fig. 2. (c).
In conclusion, we fabricated stretchable AgNW electrodes by facile and customizable selective patterning using a drop-on-demand inkjet printing or dispensing process and optimizing the adhesion balance. This method presents a promising alternative to address the challenges related with AgNW patterning, including process complexity, limited design freedom, and cost considerations. Moreover, its potential can extend to encompass a wide range of stretchable electronics applications including wearable devices.

ACKNOWLEDGEMENTS

This work was supported by the Display Center of Samsung Display and Seoul National University.

REFERENCES

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Figure 1