Fully Printed Sensors for In Situ Temperature, Heat Flow, and Thermal Conductivity Measurements in Flexible Devices.

Flexible temperature sensors allow temperature monitoring in wearable healthcare devices. A temperature sensor, which can be printed on flexible substrates, is designed and fabricated using a low-cost silver particle ink and a fast and scalable screen-printing process. A high temperature resolution of 10 m°C is reached. The versatility of this temperature sensor design is demonstrated for various applications, including in situ heat flux measurements, where a 2 mW cm-2 resolution is reached, and thermal conductivity measurements on polymer films as thin as 25 µm, with a wide range of accessible values from ∼0.1 to 0.8 W K-1 m-1.

An Alternative Anionic Polyelectrolyte for Aqueous PEDOT Dispersions: Toward Printable Transparent Electrodes.

Organic conducting polymers are promising electrode materials for printable organic electronics. One of the most studied conducting polymers is PEDOT: PSS, which is sufficiently conductive and transparent, but which shows some drawbacks, such as hygroscopicity and acidity. A new approach to stabilize PEDOT in aqueous dispersions involves the replacement of PSS with a basic polyanion based on a polystyrene backbone with (trifluoromethylsulfonyl)imide (TSFI) side groups. The PEDOT: PSTFSIK dispersions were obtained by oxidative polymerization of EDOT in an aqueous PSTFSIK solution and were characterized with regard to their composition, morphology, doping, rheological behavior, and optoelectronic performance. The PEDOT: PSTFSIK dispersions showed excellent printability and good optoelectronic performance (238 Ohm sq(-1) at 91% transmittance, σ>260 S cm(-1)) and were successfully integrated as flexible electrodes in OLED and OPV devices.

Electric field confinement effect on charge transport in organic field-effect transistors.

While it is known that the charge-carrier mobility in organic semiconductors is only weakly dependent on the electric field at low fields, the experimental mobility in organic field-effect transistors using silylethynyl-substituted pentacene is found to be surprisingly field dependent at low source-drain fields. Corroborated by scanning Kelvin probe measurements, we explain this observation by the severe difference between local conductivities within grains and at grain boundaries. Redistribution of accumulated charges creates very strong local lateral fields in the latter regions. We further confirm this picture by verifying that the charge mobility in channels having no grain boundaries, made from the same organic semiconductor, is not significantly field dependent. We show that our model allows us to quantitatively model the source-drain field dependence of the mobility in polycrystalline organic transistors.

Thin-film morphology of inkjet-printed single-droplet organic transistors using polarized Raman spectroscopy: effect of blending TIPS-pentacene with insulating polymer.

We report thin-film morphology studies of inkjet-printed single-droplet organic thin-film transistors (OTFTs) using angle-dependent polarized Raman spectroscopy. We show this to be an effective technique to determine the degree of molecular order as well as to spatially resolve the orientation of the conjugated backbones of the 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene) molecules. The addition of an insulating polymer, polystyrene (PS), does not disrupt the π-π stacking of the TIPS-Pentacene molecules. Blending in fact improves the uniformity of the molecular morphology and the active layer coverage within the device and reduces the variation in molecular orientation between polycrystalline domains. For OTFT performance, blending enhances the saturation mobility from 0.22 ± 0.05 cm(2)/(V·s) (TIPS-Pentacene) to 0.72 ± 0.17 cm(2)/(V·s) (TIPS-Pentacene:PS) in addition to improving the quality of the interface between TIPS-Pentacene and the gate dielectric in the channel, resulting in threshold voltages of ∼0 V and steep subthreshold slopes.