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Seiti, et al.
Table 1. Details of the experimental campaigns performed on the AJ P of a PEDOT: PSS ink. The first campaign is related to the study
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of line quality by varying the focusing ratio and the platen temperature. The second one deals with the study of electrical resistance and
thickness of printed samples, by varying the number of deposited layers (Platen temperature, T=40°C)
1 experimental campaign on the quality of printed lines as a function of key process parameters
st
Parameters Values
Substrate Glass slides, VWR Superfrost Plus Micro Slide
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Nozzle diameter Ø (μm) 300
Stand-off distance z (mm) 3
Printing speed s (mm/s) 25
Number of layers n (#) 10
Sample 1 printed line of length, l=10 mm
Focusing ratio R (#) 1 1.5 2
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S (sccm) 10 20 30 40 50 15 30 45 60 75 20 40 60 80 100
A (sccm) 10 20 30 40 50 10 20 30 40 50 10 20 30 40 50
Platen temp. T (°C) 25 40 60
Response Line quality q
2 experimental campaign on printing electrodes and interconnects as a function of the layer #
nd
Parameters Values
Sample Interconnect Electrode
Layer n (#) 5 10 50 100 150 1 5 10 15 20 30 40 50
R (S/A [sccm]) 1 (40 – 40) 2 (80 – 40) 1 (40 – 40) 2 (80 – 40) 2 (80 – 40)
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Substrate Glass Glass NTE substrate
Response Electrical resistance R Thickness t

ratio between the sheath gas flow, S = (0 – 200) sccm, 40, 60)°C. Each experiment was repeated 3 times. Based
and carrier gas flow, A = (0 – 50) sccm, along with the on the knowledge acquired, suitable combinations of
single contribution of these parameters, is a critical factor printing parameters for quality printing were identified,
in AJ P to ensure quality printing and high resolution. and a second experimental work was designed to study
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For a given nozzle diameter, it determines the size and the effect of the number of deposited layers, n, and platen
shape quality of the aerosol beam, along with its particle temperature, T, on the average electrical resistance, R
avg
distribution across the beam diameter. In particular, a (Ω), and average thickness, t (μm), of interconnects
avg
convergent R (R ≥ 1) is necessary to obtain a focused and electrodes. An interconnect is defined as a (single)
f
f
aerosol mist, with minimum presence of out of trajectory track connecting two contact pads, while an electrode is
droplets depositing on the edges of the printed lines, and a rectangular pad (e.g., 22 × 1 mm ), realized by printing
2
being responsible for the overspray phenomena. The consecutive layers of adjacent lines which overlap each
platen temperature, T (°C), and the number of deposited other of a given quantity. When T = 25°C, we instantly
layers, n (#), are also important to build up thickness, observed that the aerosol beam was too wet to support
achieve high conductivity and ensure print efficiency; the thick printing; on the contrary, when T = 60°C, we
platen temperature, in particular, initiates the evaporation noticed a significant shrinkage of the printed lines due
of the ink (co-) solvents (drying effect), and influences to fast drying of the ink solvent, which compromised
the ink behavior on deposition. Accordingly, a first the printing stability, especially with increased n. For
experimental work was conducted to study the effect of these reasons, the printing investigation was eventually
the printing parameter focusing ratio, R , and the platen implemented at 40°C only. The print strategy was
f
temperature, T, on the quality of single printed lines, q, eventually transferred to the NTE substrate of interest
as primary building element for electrical applications. according to the methodology described in section 2.3.
The concept of the q parameter and its determination is At least three printing repetitions were taken for each
explained in details in Section 2.2 (1). The focusing ratio combination. Electrical resistances, R, of the printed
was varied over three levels, R = (1, 1.5, 2); each of them elements were recorded by a two-point probe method
f
exploded into five sub-combinations of S and A, and then (Digital Multimeter 73 III, Fluke). Four repetitions were
combined with three levels of platen temperature T = (25, taken for each sample. Eventually, an optical microscope

International Journal of Bioprinting (2022)–Volume 8, Issue 1 53