**5.6 Slot-die coating**

It is an effective process for printing one-dimensional structures. Slot-die coating is typically integrated with the R2R system for rapid production of soft electronic devices. As shown in **Figure 7a** and **b**, the solution is pushed out of the slot-die using a pneumatic scheme, and the solution is printed laterally in the

#### **Figure 7.**

*(a) Schematic illustration of the slot-die coating technique. Reproduced with permission from Ref. [37] (b) photograph of the slot-die coating system. Reproduced with permission from Ref. [133] (c) photographs of the large-area soft OCSs having PEDOT:PSS TEs fabricated by slot-die coating. Reproduced with permission from Ref. [134] (d) photographs of the OCSs with high geometric fill factor. The employed PEDOT:PSS TEs are fabricated by slot-die coating. Reproduced with permission from Ref. [135].*

**293**

*Vacuum-Free Fabrication of Transparent Electrodes for Soft Electronics*

direction of the moving head. The thickness of the printed structure is typically determined through the solution's concentration and it's flow rate, while the head speed controls the speed of printing. PEDOT:PSS is the most commonly processed TE material for slot-die coating. **Figure 7c** and **d** display flexible large-area OSCs, where, the PEDOT:PSS TEs and the organic active material were both printed by slot-die coating. [134] Key benefit of using slot-die coating is its capability to print on large-area substrates, as in slot-die coated films the center-to-edge thickness difference is negligible. Therefore, large-area OSCs having a high geometric fill factor (98.5%) were realized through integrating laser patterning with slot-die coating. [135] Besides PEDOT:PSS, slot-die coating has been effectively utilized for other conductive inks including silver NWs, [136] CNTs, [137] and graphene. [138] Similar to other processes, slot-die coating has also few limitations including, the harsh requirements regarding inks rheology for high quality coatings [139] and the

existence of high density printing defects such as ribbing and rivulet. [140]

Recent progress of the development of vacuum-free TEs for soft electronics has been promising. This chapter presents a detailed overview on the latest advances of the vacuum-free soft TEs, comprising the introduction of electrode materials classes, the optical, electrical, mechanical, and surface features of the soft TEs. The chapter summarizes the vacuum-free techniques for the fabrication of soft TEs. Regardless of all the shortcomings discussed, we are optimistic that the vacuum-free TEs be going to play vital roles in soft electronic industries in

This work was supported by the Qatar National Research Fund (a member of Qatar Foundation) under grant NPRP11S-0110-180246. The findings herein reflect

the work and are solely the responsibility of the authors.

Authors declare no conflict of interests.

*DOI: http://dx.doi.org/10.5772/intechopen.96311*

**6. Conclusions**

the future.

**Acknowledgements**

**Conflict of interest**

*Vacuum-Free Fabrication of Transparent Electrodes for Soft Electronics DOI: http://dx.doi.org/10.5772/intechopen.96311*

direction of the moving head. The thickness of the printed structure is typically determined through the solution's concentration and it's flow rate, while the head speed controls the speed of printing. PEDOT:PSS is the most commonly processed TE material for slot-die coating. **Figure 7c** and **d** display flexible large-area OSCs, where, the PEDOT:PSS TEs and the organic active material were both printed by slot-die coating. [134] Key benefit of using slot-die coating is its capability to print on large-area substrates, as in slot-die coated films the center-to-edge thickness difference is negligible. Therefore, large-area OSCs having a high geometric fill factor (98.5%) were realized through integrating laser patterning with slot-die coating. [135] Besides PEDOT:PSS, slot-die coating has been effectively utilized for other conductive inks including silver NWs, [136] CNTs, [137] and graphene. [138] Similar to other processes, slot-die coating has also few limitations including, the harsh requirements regarding inks rheology for high quality coatings [139] and the existence of high density printing defects such as ribbing and rivulet. [140]
