Daniel Tobjörk

Low-Cost Hydrogen Sulfide Gas Sensor on Paper Substrates: Fabrication and Demonstration

Drop-cast deprotonated emeraldine base (poly)aniline (PANI)-copper chloride films on paper substrates containing ink-jet printed silver electrodes have been prepared and are shown to be promising low-cost gas-sensors for H2S at room temperature. These films showed large changes in the conductivity (three to four orders of magnitude) upon exposure to low concentrations of H2S (10 ppm) due to the formation of CuS and concurrent protonation of PANI. This large response of the sensor can be explained by the relatively large roughness and porosity of this paper substrate. Furthermore, the minimum resistances are low enough to allow light emitting diode lamps to be switched on using a low-voltage battery, thus serving as a proof-of-concept for mass-produced H2S-sensors for, for example, the food packaging industry.

Absence of substrate roughness effects on an all-printed organic transistor operating at one volt

A hygroscopic insulator transistor (HIFET) operating at 1V was manufactured using roll-to-roll techniques on a rough, low-cost plastic substrate. The effects of the substrate roughness on the active channel were studied by using two different plastic substrates and comparing HIFETs and organic field-effect transistors (OFETs). We found that the HIFET, as opposed to OFETs, is rather insensitive to changes in the roughness of plastic substrates. Hence, a robust feature of ion modulated transistors is shown.

Roll-to-Roll Fabrication of Bulk Heterojunction Plastic Solar Cells using the Reverse Gravure Coating Technique

The roll-to-roll reverse gravure (RG) coating technique was used to produce thin homogeneous films (∼100 nm) for organic bulk heterojunction solar cells. The conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and the active layer regioregular poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C 61 -butyric acid methyl ester (P3HT:PCBM) were successfully subsequently RG coated on an ITO covered plastic substrate in ambient air. Working solar cells were achieved after annealing and thermal evaporation of the top contact. The AM1.5 power conversion efficiency (PCE) of the RG coated organic solar cells was determined to 0.74% (at 100 mW/cm 2 ). This was very similar to the results of a reference device that was spin coated on a glass substrate in a nitrogen glove box.

Towards printed magnetic sensors based on organic diodes

We report a study of magnetotransport properties of regio-regular poly(3-hexyl thiophene) (RRP3HT)-based organic diodes. The devices were fabricated using two different techniques namely spin coating and inkjet printing. Positive magnetoresistance (MR) effect was observed at room temperature in all the devices. The highest MR magnitude reached up to 16% for some spin-coated devices and up to 10% in inkjet printed devices. The MR magnitude and line shapes were found to depend strongly on the measuring current. We observed deviation from the theoretically predicted Lorentzian or non-Lorentzian line shape of the MR traces, which is discussed in detail in the article. Although, the printed devices exhibit MR response as high as for the spin-coated ones, they still need to be optimised in terms of performance and yield for large scale applications as magnetic sensors.

Low-cost hydrogen sulfide gas sensor on paper substrates; fabrication and demonstration

Drop-casted deprotonated Emeraldine base (poly)aniline (PANI) - copper chloride films on paper substrates containing ink-jet printed silver electrodes have been prepared and are shown to be promising low-cost gas-sensors for H2S at room temperature. These films showed large changes in the conductivity (three to four orders of magnitude) upon exposure to low concentrations of H2S (10ppm) due to the formation of CuS and concurrent protonation of PANI. This large response of the sensor can be explained by the relatively large roughness and porosity of the paper substrate. Furthermore, the minimum resistances are low enough to allow LED lamps to be switched on using a low-voltage battery, thus serving as a proof-of-concept for mass-produced H2S-sensors for, for example, the food packaging industry.

Imaging and elemental analysis of polymer/fullerene nanocomposite memory devices

In this report we study the morphology and chemical composition of a nanocomposite memory device where the active device layer is sandwiched between two aluminum electrodes and consists of a nanocomposite of polystyrene (PS) and [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM). The morphology of the active layer is imaged both in plan-view and cross-sectional view by using transmission electron microscopy (TEM). We introduce two techniques to prepare the cross-sections from the active layer, namely, a conventional technique based on microtoming and secondly nanostructural processing with focused ion beam (FIB). Based on the morphology studies we deduce that within the used concentrations the PCBM forms spherical nanoscale clusters within the continuous PS matrix. The chemical composition of the device is determined by using X-ray photoelectron spectroscopy (XPS) and it shows that the thermal evaporation of the aluminum electrodes does not lead to observable inclusion of the aluminum into the active material layer.