Recent development of 3D printing technologies would provide the variety of electronic devices including environmental sensors and bio-applications. Polymer-based sensors are compatible with human-body parts or prostheses to monitor the body status of surfaces or surroundings such as temperature, humidity, and pressure. Conventional 1D or 2D fabrication processes are effective for mass production. However, specific shapes such as curvy or 3D pathways would require the 3D printed sensors to expand the possible applications.
In this study, organic temperature sensors fabricated on 3D printed surfaces are investigated to improve the device properties. 3D structures were fabricated using a DLP (direct light processing) 3D printer with photo-polymers. Sensor electrodes based on conductive carbon materials were printed on 3D shape structures. The resistances of organic temperature sensors were measured by the temperature variations. As the environmental temperature increased from 29 to 54℃, the resistance was decreased from 8.57 to 8.23 kΩ with the certain linearity, respectively. To further improvements, polymer composites comprising the inorganic nanoparticles were introduced to control the interfacial properties and the conductivity of composite carbons were improved.
Selective energy transfer from triplet states of the fluorescent blue emission layer to a red phosphorescent dye in a
neighbored triplet harvesting layer has been achieved, which has provided improved efficiency with emissions from
fluorescent and phosphorescent dyes. First of all, it is crucial to find a wide band gap host for a fluorescent blue emission
layer which has larger triplet state band gap than green or red phosphorescent dye. It was found that TcTa is a good wide
band gap host for fluorescent blue dopant(BD) and a efficient blue device was obtained. A phosphorescent red dopant
(RD) was introduced into a neighboring electron transporting layer to harvest triplet states in the fluorescent blue
emission layer and by optimizing the distance between the blue emission layer and the red triplet harvesting layer, we
have succeeded in obtaining the balanced emission of the blue and the red emissions with high efficiency from the
device structure of NPB/TcTa:BD/BAlq/BAlq:RD/BAlq/LiF/Al. The device showed maximum external quantum
efficiency of 16 % at 0.1 mA/cm2 and 13 % of external quantum efficiency, (0.29, 0.23) of CIE coordinates and 920
cd/m2 at 10 mA/cm2. To realize RGB WOLED, a fluorescent green dopant was introduced into the blue emission layer.
The RGB WOLED was successfully obtained through optimization of doping concentration for green dopant and it
showed 10 % of external quantum efficiency, (0.36, 0.36) of CIE coordinates and 1400 cd/m2 at 10 mA/cm2.
Organic thin-film transistors (TFTs) using the pentacene as an active electronic material have shown the mobility of 0.8 cm2Vs and the grains larger than 1 micrometers . Deep level transient spectroscopy (DLTS) measurements have been carried out on metal/insulator/organic-semiconductor (MIS) structure devices that have a depletion region at the insulator/organic-semiconductor interface. The very long capacitance transients were measured by the trapping of electronic charge carriers distributed in energy. Based on the DLTS characteristics, the energy levels of hole and electron traps in the obtained pentacene films were approximately Ev+0.24eV, Ev+0.31eV, and Ec- 0.69eV.
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