Abstract
Organic light-emitting diodes (OLEDs) have been successfully introduced to the smartphone display market and have geared up to become contenders for applications in general illumination where they promise to combine efficient generation of white light with excellent color quality, glare-free illumination, and highly attractive designs. Device efficiency is the key requirement for such white OLEDs, not only from a sustainability perspective, but also because at the high brightness required for general illumination, losses lead to heating and may, thus, cause rapid device degradation. The efficiency of white OLEDs increased tremendously over the past two decades, and internal charge-to-photon conversion can now be achieved at ∼100% yield. However, the extraction of photons remains rather inefficient (typically <30%). Here, we provide an introduction to the underlying physics of outcoupling in white OLEDs and review recent progress toward making light extraction more efficient. We describe how structures that scatter, refract, or diffract light can be attached to the outside of white OLEDs (external outcoupling) or can be integrated close to the active layers of the device (internal outcoupling). Moreover, the prospects of using top-emitting metal–metal microcavity designs for white OLEDs and of tuning the average orientation of the emissive molecules within the OLED are discussed.
Highlights
The idea of using organic compounds with extended conjugated electron systems for efficient, sustainable, and flexible generation of light has fascinated scientists around the world for nearly three decades
organic light-emitting diodes (OLEDs) were initially developed mostly as the active element in emissive displays, the technology has matured to a level that brings within reach applications in general lighting, a field that poses in many regards much stricter requirements on device performance
We review the recent progress in the field of white OLEDs, with particular emphasis on recent developments for improved outcoupling
Summary
The idea of using organic compounds with extended conjugated electron systems for efficient, sustainable, and flexible generation of light has fascinated scientists around the world for nearly three decades now. The idea of using organic compounds with extended conjugated electron systems for efficient, sustainable, and flexible generation of light has fascinated scientists around the world for nearly three decades Within this timeframe, the efficiency, brightness, and stability of organic light-emitting diodes (OLEDs) have improved dramatically. General lighting requires OLEDs to generate balanced white emission, produce high brightness levels, and to do so at competitive efficiency when compared to established technology, in particular, fluorescent lamps and conventional LEDs. For many years, a primary focus has been to improve the internal efficiency of OLEDs, i.e., the yield of charge-to-photon conversion. We will discuss the prospect of white top-emitting OLEDs and work on tuning the spatial orientation of the light-emitting molecules within the device to further enhance light extraction efficiency
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