posted on 2024-02-20, 03:29authored byJonathan
D. Nguyen, Satish Kumar, C. Daniel Frisbie, Lorraine F. Francis
Liquid-applied coating and printing
methods are attractive
options
for the production of large-area, low-cost flexible electronics. However,
controlling the deposited functional layer thickness and uniformity,
particularly at submicrometer thicknesses, is challenging. This study
focuses on thickness uniformity and control in Schottky diodes made
by self-aligned capillarity-assisted lithography for electronics (SCALE).
SCALE combines UV imprinting to structure a substrate surface and
inkjet printing of functional inks to make flexible electronic devices.
In the diode described here, the key functional layer is the poly(3-hexylthiophene-2,5-diyl)
(P3HT) semiconductor, which was deposited from a 1,2-dichlorobenzene
solution. Thin, uniform P3HT layers with no shorts are required for
optimal diode performance. Thickness nonuniformities in the P3HT layer,
including the coffee-ring effect and lack of planarization over adjacent
electrode channels, occurred during drying. These nonuniformities
were most severe when drying was carried out at elevated temperatures
(≥50 °C). By drying P3HT layers at 23 °C, the film
uniformity and planarization improved significantly, and the device
yield was nearly 8× higher. P3HT layers less than 300 nm thick
were demonstrated. The improvements in uniformity and planarization
are discussed in terms of the competition between solvent evaporation
and P3HT diffusion. Self-aligned, printed Schottky diodes demonstrated
up to 4.0 × 104 rectification ratio at ±1 V,
minimal hysteresis, and ∼0.3 V turn-on voltage.