Gong Gu

High-external-quantum-efficiency organic light-emitting devices

We study the internal and external quantum efficiencies of vacuum-deposited organic light-emitting devices (OLEDs). The internal quantum efficiency of OLEDs based on tris-(8-hydroxyquinoline) aluminum is calculated to be 5.7 times the observed external quantum efficiency ?(e), consistent with measurements. We demonstrate a shaped substrate that increases ?(e) by a factor of 1.9+/-0.2 over similar OLEDs fabricated upon flat glass substrates and leads to a 100%-emissive aperture, i.e., the emitting area completely occupies the display area even in the presence of metal interconnects. We also discuss a substrate structure that increases ?(e) by an additional factor of 2. The high device efficiencies are promising for developing OLED-based displays with extremely low power consumption and increased operational lifetime.

Achieving full-color organic light-emitting devices for lightweight, flat-panel displays

We review recent results in the field of organic light-emitting devices (OLEDs), with particular attention to the application of organic light-emitting devices to ultra-lightweight, full color, flat-panel displays. We show that OLED brightness, efficiency, operating voltage, and lifetime is sufficient to compete with other flat-panel display technologies such as backlit liquid crystal displays. We describe a novel, tunable OLED consisting of vertically stacked, transparent light-emitting devices which can serve as a color-tunable element in high-resolution full-color display., In addition, the unique physical properties of organic thin films allow for flexible, conformable, or foldable displays which are unobtainable with conventional, inorganic semiconductor technologies.

Design of flat-panel displays based on organic light-emitting devices

We provide a systematic and quantitative analysis of the design of flat-panel displays (FPDs) based on organic light-emitting devices (OLEDs). Key performance parameters are estimated for OLED-based displays; system issues, including addressing schemes and strategies required to achieve full-color displays, are treated quantitatively. Furthermore, addressing schemes for recently demonstrated, full-color high-resolution stacked OLEDs are discussed. Our analysis shows that OLED technology is suitable for many FPD applications, and can provide performance superior to that achieved using alternative display technologies.

Semitransparent cathodes for organic light emitting devices

We optimize transparent organic light emitting devices (TOLEDs) using compound cathodes consisting of a thermally evaporated metal contact layer capped with indium–tin–oxide (ITO). The ITO is sputtered at rates of up to 1.6 A/s using a high power radio frequency magnetron process. With a Mg:Ag contact layer, we demonstrate a TOLED with 50% transparency and an operating voltage within 0.3 V of a device with identical organic layers and a conventional Mg:Ag cathode. The operational lifetime of the TOLED is shown to be equal to that of a similar, nontransparent device. We also study the effects of using different contact metals, including Ca, Al and LiF, on the operating characteristics of the TOLEDs. With a thin Ca contact layer, undoped TOLEDs with >80% peak transparency operating at (5.9±0.1) V at a brightness of >100 cd/m2 are demonstrated. These devices have application to transparent, head-up displays and to full color, stacked organic light emitting devices.

A METAL-FREE, FULL-COLOR STACKED ORGANIC LIGHT-EMITTING DEVICE

We report the demonstration of a transparent, completely metal-free, full-color stacked organic light-emitting device (SOLED). The SOLED emits light from both top and bottom (substrate) surfaces with total external quantum efficiencies of 0.65%, 1.3%, and 2.2% for the green, blue, and red stacked subpixels, respectively. The respective top emission quantum efficiencies for the three subpixels are 0.23%, 0.63%, and 1.6%. The angular dependence of emission colors due to microcavity effects is weak when viewed from the top device surface. This metal-free SOLED is from 21% to 50% transparent over the entire visible spectral range. Capability for top emission makes this device suitable for integration with electronic components in active matrix display backplanes.

High-efficiency, low-drive-voltage, semitransparent stacked organic light-emitting device

We report a semitransparent, two-color, stacked organic light-emitting device (SOLED) with high efficiency, low drive voltage, and minimal color distortion. The SOLED emits light from both device surfaces. The external quantum efficiencies of the green and red stacked elements are 1% and 0.4%, respectively, where only the photons emitted from the substrate surface are collected. The drive voltage for the top stack element is decreased to ∼12 V by using a modified indium tin oxide thin film deposition process. Color distortion and angular dependence of the emission spectra are minimal.

The stacked OLED (SOLED): a new type of organic device for achieving high-resolution full-color displays

Abstract We describe a novel organic light-emitting device (OLED) in which color, grey scale and intensity can be independently achieved. The device consists of three separately contacted, red-, green-and blue-emitting OLEDs placed in a vertical stack and separated by transparent, conducting electrodes. The stacked OLED (or SOLED) is shown to efficiently generate a high-intensity optical output whose color is a linear superposition of spectra of the individual emitting elements in the device. Optical microcavity effects are found to distort the output spectrum in non-optimized SOLEDs. To our knowledge, the SOLED architecture provides the highest efficiency and resolution, as well as the simplest means for fabricating full-color displays based on small molecular weight organic materials demonstrated to date.

Control of microcavity effects in full color stacked organic light emitting devices

We model a three-color stacked organic light emitting device (SOLED) and determine the influence of microcavity effects on the color saturation of the layered, light emitting elements. Using the model, we design and demonstrate a SOLED with good color saturation and minimal viewing angle effects. The Commission Internationale de L’Eclairage chromaticity coordinates for the red, green, and blue subpixels of the SOLED are (0.68, 0.32), (0.32, 0.53), and (0.14, 0.19), respectively. The full color SOLED opens a path to full color, lightweight displays utilizing vertically stacked color elements to maximize the resolution and aperture ratio of the display.

Transparent stacked organic light emitting devices. II. Device performance and applications to displays

Vertical stacking of organic light emitting devices (OLEDs) that emit the three primary colors is shown to be a means for achieving efficient and bright full-color displays. In Paper I, we addressed stacked OLED (SOLED) design and fabrication principles to optimize emission colors, operating voltage, and efficiency. Here, we present results on two different (metal-containing and metal-free cathode) SOLED structures that exhibit performance suitable for many full-color display applications. The operating voltages at 10 mA/cm2 (corresponding to video display brightnesses) are 6.8, 8.5, and 12.1 V for the red (R), green (G), and blue (B) elements of the metal-containing SOLED, respectively. The respective subpixel luminous efficiencies are 0.53, 1.44, and 1.52 cd/A, and the Commission Internationale de L’Eclairage (CIE) chromaticity coordinates are (0.72, 0.28), (0.42, 0.56), and (0.20, 0.22). In the high transparency metal-free SOLED, an insulating layer was inserted between the two upper subpixels to allow...

Light emitting devices using vacuum deposited organic thin films

We review some recent results from novel light emitting heterostructures made from vacuum deposited organic semiconductors. The ability to grow these materials in amorphous or quasi epitaxial thin films on a variety of substrates, and their unique optoelectronic properties, create device applications unobtainable with conventional inorganic materials.