D. Metzdorf

Inverted top-emitting organic light-emitting diodes using sputter-deposited anodes

We demonstrate vacuum-sublimed topside-emitting inverted organic light-emitting diodes (IOLEDs) employing low-power radio-frequency magnetron sputter-deposited indium tin oxide (ITO) anodes. The device introduces a two-step sputtering sequence to reduce damage incurred by the sputtering process, paired with a buffer- and hole-transporting material Pentacene. Systematic optimization of the organic growth sequence focused on device performance characterized by current and luminous efficiencies, suggest the incorporation of rather thick Pentacene layers. The optimized thickness is obtained as a trade-off between light absorption and protective properties of Pentacene. The optically and electrically undoped organic multilayer devices capped with 90-nm ITO exhibit high current efficiencies of 3.9 cd/A at a raised luminance level of 1.500 cd/m2, combined with luminous efficiencies of 0.7 lm/W. The inverted configuration allows for integration of organic light-emitting diodes (OLEDs) with preferentially used n-c...

Vertical channel all-organic thin-film transistors

Technologically simple and cost-effective processes are essential for the fabrication of organic electronic devices. In this letter, we present a concept for making vertical channel all-organic thin-film transistors on glass substrate. This concept avoids the need for patterning processes with high lateral resolution by defining the channel length through the thickness of an insulating layer. Our devices are based on commercially available poly(ethylene dioxythiophene)/poly(styrene sulfonate) dispersion for source, drain, and gate electrodes, photoresist as the insulating layer and photosensitized poly(vinyl alcohol) as the gate insulator. Pentacene was used as the organic semiconductor. Functional devices with channel length of 2.4 μm and width of 1 mm have been realized, and we report electrical characteristics of these devices.

All-organic thin-film transistors patterned by means of selective electropolymerization

We have fabricated fully patterned all-organic thin-film transistors on polyimide substrates using selectively electropolymerized poly (3,4-ethylenedioxythiophene) doped with poly (styrene sulfonate) (PEDOT:PSS) for the source and drain contacts, PEDOT:PSS Baytron P dispersion for the gate electrodes, poly (4-vinyl phenol) or polyvinyl alcohol for the gate dielectric layers, and pentacene or poly (3-butylthiophene) for the organic active layers. We have built top-gate structures with gates printed on top of the gate dielectric layer. Carrier mobilities as large as 0.01 cm2/V s were measured. Functional all-organic transistors have been realized using a simple and potentially inexpensive technology that does not depend on photolithographical processes and that allows the preparation of feature sizes on the micrometer scale.

OLED matrix displays: in-line process technology and fundamentals

Abstract For more than a decade considerable effort has been put into the development of light emitting devices based on evaporated layers of organic semiconductors. To date, the properties of matrix displays consisting of organic light emitting diodes (OLEDs) basically meet automotive and consumer product requirements. OLED matrix displays offer high contrast, wide viewing angle and a broad temperature range at low power consumption. Due to the sensitivity of organic thin films, device structuring by conventional etching techniques is not feasible and alternative structuring techniques were developed. To meet industrial demands for device fabrication an in-line-OMBD was developed. For the first time ever, a fully in-line processed OLED is presented. Electrical current in organic devices is limited by the low conductivity of organic semiconductors and by energy barriers at the metal–organic semiconductor interface. Photoelectric measurements facilitate the determination of barrier height differences between various electrode setups. Further insight in the energy band alignment at organic heterointerfaces is gained by ultraviolet photoelectron spectroscopy (UPS). In addition to widely employed electrical ( I – V , C – V ) and optical ( P – I ) measurements, thermally stimulated current (TSC) and luminescence (TSL) allow the characterization and a more detailed understanding of carrier traps and charge transport in organic devices. Energy transfer in a doped OLED emitting layer can be investigated by time-resolved photoluminescence measurements.

OLED matrix displays: technology and fundamentals

For more than a decade, considerable effort has been put into the development of light emitting devices based on evaporated layers of organic semiconductors. To date, the properties of matrix displays consisting of organic light emitting diodes (OLEDs) basically meet automotive and consumer product requirements. OLED matrix displays offer high contrast, wide viewing angle and a broad temperature range at low power consumption. In contrast to polymer devices, OLEDs are processed in ultrahigh vacuum systems. The organic source materials are sublimated from effusion cells. Due to the sensitivity of organic thin films, device structuring by conventional etching techniques is not feasible and alternative structuring techniques were developed. Electrical current in organic devices is limited by the low conductivity of organic semiconductors and by energy barriers at the metal-organic semiconductor interface. Photoelectric measurements facilitate the determination of barrier height differences between various electrode set-ups. Further insights into the energy band alignment at organic heterointerfaces are gained by ultraviolet photoelectron spectroscopy (UPS). In addition to widely employed electrical (I-V, C-V) and optical (PI) measurements, thermally stimulated current (TSC) and luminescence (TSL) allow the characterization and a more detailed understanding of carrier traps and charge transport in organic devices. Energy transfer in a doped OLED emitting layer can be investigated by time-resolved photoluminescence measurements.

Spatially selective flash sublimation of small organic molecules for organic light-emitting diodes and display applications

A flash-sublimation technique for the spatially selective deposition of small organic molecules is presented. Single-pulse electrically heated copper stripes (width 100 μm) serve as heating elements. The relevant time scale of our technique is on the order of milliseconds. Under high vacuum conditions, the heating elements are used to locally flash-sublimate small-molecule material from a previously coated polyimide foil onto a (ITO-)glass substrate, positioned at a vertical distance of 60 μm. The spatial resolution in our nonoptimized experiments was 250 μm. Organic light-emitting diode (OLED) devices with flash-deposited tris-(8-hydroxyquinoline)aluminum (Alq3) as the active material are demonstrated with satisfying electrical and optical properties. Flash sublimation of a stacked nonintermixed Alq3 (30 nm) [2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5Hbenzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene]propane-dinitrile (DCM2) (1 nm)/Alq3 (30 nm) layer is shown to yield a red-emitting (λ=624 nm) DCM2-doped ...