Abstract
In recent years, the organic light-emitting diode (OLED) technology has been a rapidly evolving field of research, successfully making the transition to commercial applications such as mobile phones and other small portable devices. OLEDs provide efficient generation of light, excellent color quality, and allow for innovative display designs, e.g., curved shapes, mechanically flexible and/or transparent devices. Especially their self emissive nature is a highly desirable feature for display applications. In this work, we demonstrate an approach for full-color OLED pixels that are fabricated by vertical stacking of a red-, green-, and blue-emitting unit. Each unit can be addressed separately which allows for efficient generation of every color that is accessible by superpositioning the spectra of the individual emission units. Here, we use a combination of time division multiplexing and pulse width modulation to achieve efficient color mixing. The presented device design requires only three independently addressable electrodes, simplifying both fabrication and electrical driving. The device is built in a top-emission geometry, which is highly desirable for display fabrication as the pixel can be directly deposited onto back-plane electronics. Despite the top-emission design and the application of three silver layers within the device, there is only a minor color shift even for large viewing angles. The color space spanned by the three emission sub-units exceeds the sRGB space, providing more saturated green/yellow/red colors. Furthermore, the electrical performance of each individual unit is on par with standard single emission unit OLEDs, showing very low leakage currents and achieving brightness levels above 1000 cd/m2 at moderate voltages of around 3–4 V.
Highlights
Displays based on organic light-emitting diodes (OLEDs) are rapidly evolving into serious competitors to the current state-of-the-art liquid crystal display (LCD) technology and can already be found in mobile phones and television screens
The n-side of the blue-emitting unit is connected to a positive potential and the p-side of the green unit is on a negative potential
A more preferable state-of-the-art driving scheme based on current instead of voltage can be applied to our design as well
Summary
Displays based on organic light-emitting diodes (OLEDs) are rapidly evolving into serious competitors to the current state-of-the-art liquid crystal display (LCD) technology and can already be found in mobile phones and television screens. In a typical flat-panel display (LCD or OLED display), each pixel consists of laterally separated red (R), green (G), and blue (B) sub-pixels in a side-by-side geometry. Creating the sub-pixel pattern requires complex and delicate fine metal shadow mask technology or the use of laminated color filters. The latter limits overall device efficiency and the former struggles to provide the accuracy required for the smaller pixel size and higher pixel density of generation OLED displays. The most important work on this topic has been published almost two decades ago, when compared to current state-of-the-art display technology, the devices have only rather low brightness, poor electrical performance, low efficiency, and only mediocre color gamut[1,2]
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