Integrating sphere charge coupled device-based measurement method for organic light-emitting devices

An integrating sphere charge coupled device (CCD)-based measurement system has been developed to accurately characterize the optoelectronic performance of organic polymer light-emitting devices (PLEDs). By theoretically analyzing a previously developed lens-coupled method and comparing it with the integrating sphere CCD-based method, we have found that the integrating sphere-based measurement method provides more stable reliable optical data in comparison with the lens-coupled measurement method. In addition, we demonstrate that inappropriate calibration of the PLED measurement system can greatly exaggerate device performance. © 2003 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71158/2/RSINAK-74-7-3572-1.pd

Optoelectrical properties of four amorphous silicon thin-film transistors 200 dpi active-matrix organic polymer light-emitting display

We report on opto-electrical properties of a current-driven 200 dpi active-matrix organic polymer red light-emitting display (AM–PLED) based on four hydrogenated amorphous silicon thin-film transistor pixel electrode circuits. The AM–PLED luminance and effective light-emission efficiency were 30 cd/m230cd/m2 and 0.3 cd/A, respectively, at the data current equal to 25 mA. The display electroluminescent spectrum has a peak located at and the full width at half maximum value of 644 and 95 nm, respectively, and Commission Internationale de l’Eclairage color coordinates of (0.66,0.33). © 2003 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70464/2/APPLAB-83-16-3233-1.pd

Distortion-Free Stretchable Light-Emitting Diodes via Imperceptible Microwrinkles

Stretchable organic light-emitting diodes (OLEDs) have been considered as a promising technology for next-generation free-form and wearable displays. However, an approach to ensure both high device performance and high resolution has not yet been suggested. While introducing a wrinkled structure in the active pixel areas is a decent method, the formation of out-of-plane macroscopic wrinkles having a wavelength of a few hundred mu m has caused distortion in the shape of the pixel, which is a critical drawback for a matrix-configured display demanding a sharp pixel definition. Herein, microwrinkled OLEDs are fabricated to define a distortion-free pixel by direct deposition of OLEDs on biaxially prestretched elastomeric substrate, being feasible by a low-temperature-based solution process. The total thickness of the device can be significantly reduced up to 350 nm, producing the imperceptible microwrinkles having a wavelength under 20 mu m. The microwrinkled OLEDs show a luminance over 8000 cd m(-2) and maximum current efficiency of 7.76 cd A(-1), which is comparable to the device without wrinkled structure. Finally, a stretchable 4 x 4 OLED pixel array with a microwrinkled structure is demonstrated showing sharply defined square-patterned emission, proving the potential in the future high-resolution stretchable display.N

Active‐matrix organic light‐emitting displays employing two thin‐film‐transistor a‐Si:H pixels on flexible stainless‐steel foil

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92136/1/1.2759547.pd

Selective crack formation on stretchable silver nano-particle based thin films for customized and integrated strain-sensing system

Wrinkle structure effectively suppresses the crack formation in a material under tensile strain, thus enabling intrinsically brittle material to be strain-tolerant. If the brittle nature of the material can be selectively engineered on the wrinkle structure, combination of mechanically different structures can be obtained within the same material. In this work, we introduce a simple and facile approach to effectively turn strain-tolerant conductive metal thin film with wrinkle structure into crack-rich thin film. The intended phenomenon was controlled by additionally inkjet-printing Ag thin film onto the wrinkle structure, and the structure and performance were also systematically optimized to enhance sensitivity and stability of the sensor. Our strategy to induce intended cracks on corrugated metal thin film enables not only to stably combine stretchable interconnectors and strain sensors but also to fabricate an integrated strain sensor system that can be custom-tailored to the subject's hand size. We believe the facile strategy will be a good step to realize an integrated strain sensor system.N

Substrate thermal conductivity effect on heat dissipation and lifetime improvement of organic light-emitting diodes

We report substrate thermal conductivity effect on heat dissipation and lifetime improvement of organic light-emitting diodes (OLEDs). Heat dissipation behavior of top-emission OLEDs fabricated on silicon, glass, and planarized stainless steel substrates was measured by using an infrared camera. Peak temperature measured from the backside of each substrate was saturated to be 21.4, 64.5, and 40.5 °C, 180 s after the OLED was operated at luminance of 10 000 cd/m2 and 80% luminance lifetime was about 198, 31, and 96 h, respectively. Efficient heat dissipation through the highly thermally conductive substrates reduced temperature increase, resulting in much improved OLED lifetime.This work supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD, Basic Research Promotion Fund) (Grant No. KRF-2008-331-D00216)

Optoelectronic properties of poly(fluorene) co‐polymer light‐emitting devices on a plastic substrate *

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92131/1/1.2150379.pd

Multidipping Technique for Fabrication Time Reduction and Performance Improvement of Solution-Processed Single-Walled Carbon Nanotube Thin-Film Transistors

Herein, a simple and effective technique, "multidipping technique," is implemented to rapidly form random networks of single-walled carbon nanotubes (SWCNTs) used as a channel material in solution-processed thin-film transistors (TFTs). The multidipping process consists of repetition of dipping a substrate into a dispersed semiconducting SWCNT solution and rinsing the substrate between each dipping process. Compared with the conventional dipping method, this technique reduces total deposition time required to form high-quality SWCNT networks by more than half and simultaneously improves the electrical performances of SWCNT TFTs. These phenomena are also comprehensively analyzed with experiments and microscopic images of the channel region, which well show morphology of the SWCNT networks. It is believed that the low-temperature process and facile deposition method of SWCNT networks can provide a guideline for high-throughput fabrication of high-performance SWCNT TFT arrays in flexible active matrix sensor array and display applications.N

Inkjet-Printed Silver Gate Electrode and Organic Dielectric Materials for Bottom-Gate Pentacene Thin-Film Transistors

An inkjet-printed silver electrode and a spin-coated cross-linked poly(4-vinylphenol)(PVP) dielectric layer were used as a gate electrode and a gate insulator for a bottom-gate pentacene thin-film transistor (TFT), respectively. The printing and the curing conditions of the printed silver electrode were optimized and tested on various substrates, such as glass, silicon, silicon dioxide, polyethersulfone, polyethyleneterephthalate, polyimide and polyarylate, to produce a good sheet resistance of 0.2 $\sim$ 0.4 $\Omega$/$\square$ and a good surface roughness of 2.38 nm in RMS value and 20.14 nm in peak-to-valley (P2V) value, which are very similar to those of conventionally-sputtered indium-tin-oxide (ITO) or thermally-evaporated silver electrodes. The coated PVP layer of metal/PVP/metal devices showed a good insulation property of 10.4 nA/$\rm cm^{2}$ at 0.5 MV/cm. The PVP layer further reduced the surface roughness of the gate electrode to provide a good interface to the pentance layer. The pentacene TFT with a structure of glass/printed silver/PVP/pentacene/Au showed a good saturation region mobility of 0.13 $\rm cm^{2}$/Vs and a good on/off ratio of larger than 10$^{5}$, which are similar to the performance of a pentacene TFT with a conventional ITO gate electrode.This work was supported by \SystemIC2010" project of Korea Ministry of Knowledge Economy and by the Seoul R&BD Program (CRO70048)