In recent years, additive manufacturing has been evolving towards flexible substrates for the fabrication of printable electronic devices and circuits. Generally polymer-based, these emerging substrates suffer from their heat sensitivity and low glass-transition temperatures. As such they require new highly-localized sintering processes to treat the electronic inks without damaging the polymer-based substrate. Laser-based sintering techniques have shown great promises to achieve high-quality sintering locally, while controlling the heat penetration to preserve the polymer substrates integrity. In this report, we explore new optimization pathways for dynamic laser-based sintering of conductive silver inks. Multiple passes of a pulsed laser are first performed while varying pulse train frequencies and pulse energies as an attempt to optimize the properties of the silver inks. Then, time-domain pulse shaping is performed to alter the properties of the conductive inks. Together, these pathways allow for the careful control of the time-domain laser energy distribution in order to achieve the best electronic performances while preserving the substrate’s integrity. Sheet resistance values as low as 0.024Ω/□ are achieved, which is comparable to conventional 1-hour oven annealing, with the processing time dramatically reduced to the milisecond range. These results are supported by finite element modeling of the laser-induced thermal dynamics.
Active inkjet materials are invoked in the fabrication of optoelectronic devices. These types of multilayer assemblies contain a variety of commercially available ink formulations. It is envisioned that a dielectric SU-8 material can be used in a FET-like structure to form an interlayer between conductive silver and semi-conductive MWCNT-doped PEDOT:PSS ink layers. These printed structures may be fabricated onto a polyimide based flexible substrate, for instance. These structures are a starting point for offering valuable information on layer-on-layer printing interactions and interface problematics within a complete inkjet device fabrication.
The printing of an efficient thermistor temperature sensor by using self-doped conducting polymers has been achieved. The use of a water-soluble polymer as the active material allows printing and processing in green solvents. The sensor showed a good sensitivity to temperature variations, with a temperature coefficient of resistance (TCR) of -1.3%. The sensor also exhibited a better stability and reversibility towards humidity compared to the state-of-the-art PEDOT:PSS.
We show flexible bolometer devices produced entirely using digital inkjet printing on polymer substrates. The bolometers consist of a silver interdigital electrode thermistor covered with a methylammonium lead trihalide perovskite absorber layer which shows good absorber characteristics at visible wavelengths. Both the standalone thermistor and the complete bolometer devices show polymer PTC thermistor-like behavior over a temperature range of 17 to 36 °C, with a change in resistance up-to six orders of magnitude over this temperature range. The addition of the perovskite absorber to the thermistor structure provides the illumination-dependent behavior proper to bolometers.
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