Inkjet Printed, High Mobility Inorganic-Oxide Field Effect Transistors Processed at Room Temperature

Printed electronics (PE) represents any electronic devices, components or circuits that can be processed using modern-day printing techniques. Field-effect transistors (FETs) and logics are being printed with intended applications requiring simple circuitry on large, flexible (e.g., polymer) substrates for low-cost and disposable electronics. Although organic materials have commonly been chosen for their easy printability and low temperature processability, high quality inorganic oxide-semiconductors are also being considered recently. The intrinsic mobility of the inorganic semiconductors are always by far superior than the organic ones; however, the commonly expressed reservations against the inorganic-based printed electronics are due to major issues, such as high processing temperatures and their incompatibility with solution-processing. Here we show a possibility to circumvent these difficulties and demonstrate a room-temperature processed and inkjet printed inorganic-oxide FET where the transistor channel is composed of an interconnected nanoparticle network and a solid polymer electrolyte serves as the dielectric. Even an extremely conservative estimation of the field-effect mobility of such a device yields a value of 0.8 cm2/(V s), which is still exceptionally large for a room temperature processed and printed transistor from inorganic materials

Ultraviolet photodetector arrays assembled by dielectrophoresis of ZnO nanoparticles

Sensitive and fast ultraviolet sensor arrays have been produced by dielectrophoretic assembling of ZnO nanoparticles. The sub-micron device dimensions induce low operating voltage and low power consumption. The devices are long-term stable and operate in air, oxygen and nitrogen. We have determined the absorption and desorption dynamics from the time-resolved photoresponse and conclude that oxygen or carbon dioxide are the photodesorbed species. We could derive the charge carrier concentration and mobility of the device from measurements of the low-bias and high-bias photocurrent. The presence of defects is discussed by comparing electroluminescence spectra from biased devices with photoluminescence spectral maps of ZnO dispersions

Investigation of Solution-Processed Ultrathin Electron Injection Layers for Organic Light-Emitting Diodes

We study two types of water/alcohol-soluble aliphatic amines, polyethylenimine (PEI) and polyethylenimine-ethoxylated (PEIE), for their suitability as electron injection layers in solution-processed blue fluorescent organic light-emitting diodes (OLEDs). X-ray photoelectron spectroscopy is used to determine the nominal thickness of the polymer layers while ultraviolet photoelectron spectroscopy is carried out to determine the induced work-function change of the silver cathode. The determined work-function shifts are as high as 1.5 eV for PEI and 1.3 eV for PEIE. Furthermore, atomic force microscopy images reveal that homogeneous PEI and PEIE layers are present at nominal thicknesses of about 11 nm. Finally, we solution prepare blue emitting polymer-based OLEDs using PEI/PEIE in combination with Ag as cathode layers. Luminous efficiency reaches 3 and 2.2 cd A^–1, whereas maximum luminance values are as high as 8000 and 3000 cd m^–2 for PEI and PEIE injection layers, respectively. The prepared devices show a comparable performance to Ca/Ag OLEDs and an improved shelf lifetime

Investigation of Solution-Processed Ultrathin Electron Injection Layers for Organic Light-Emitting Diodes

We study two types of water/alcohol-soluble aliphatic amines, polyethylenimine (PEI) and polyethyleni-mine-ethoxylated (PEIE), for their suitability as electron injection layers in solution-processed blue fluorescent organic light-emitting diodes (OLEDs). X-ray photoelectron spectroscopy is used to determine the nominal thickness of the polymer layers while ultraviolet photoelectron spectroscopy is carried out to determine the induced work-function change of the silver cathode. The determined work-function shifts are as high as 1.5 eV for PEI and 1.3 eV for PEIE. Furthermore, atomic force microscopy images reveal that homogeneous PEI and PEIE layers are present at nominal thicknesses of about 11 nm. Finally, we solution prepare blue emitting polymer-based OLEDs using PEI/PEIE in combination with Ag as cathode layers. Luminous efficiency reaches 3 and 2.2 cd A−1, whereas maximum luminance values are as high as 8000 and 3000 cd m−2for PEI and PEIE injection layers, respectively. The prepared devices show a comparable performance to Ca/Ag OLEDs and an improved shelf lifetime