Recent advances in light outcoupling from white organic light-emitting diodes

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.

Exploiting the Potential of OLED-Based Photo-Organic Sensors for Biotechnological Applications

“…This is especially important in top-emitting devices where the cathode is composed of a thin semitransparent metal layer such as Ag. The device efficiency can be doubled [15] by applying additional light out-coupling measures.…”

Enhanced Outcoupling in Organic Light-Emitting Diodes via a High-Index Contrast Scattering Layer

“…Outcoupling efficiency can be calculated with the aid of advanced modeling techniques 14-16 which show that only approximately 20-30% of emitted photons escape a noncavity planar OLED fabricated on a conventional glass substrate. [17][18][19] Hence, in order to fully convert the input electrical power into optical power, it is essential to overcome this low outcoupling efficiency.It should be noted that two factors are closely associated with typically low OLED outcoupling efficiency: the planarity of the device and refractive indices of the thin film stack. A planar organic/metal interface leads to evanescently coupled surface plasmonic losses, 20 while an index gradient starting from high-index organic layers to mid-index glass substrate to low-index ambient air leads to laterally travelling waveguided and substrate-trapped loss modes.…”

“…Outcoupling efficiency can be calculated with the aid of advanced modeling techniques 14-16 which show that only approximately 20-30% of emitted photons escape a noncavity planar OLED fabricated on a conventional glass substrate. [17][18][19] Hence, in order to fully convert the input electrical power into optical power, it is essential to overcome this low outcoupling efficiency.…”

“…Outcoupling efficiency can be calculated with the aid of advanced modeling techniques [14][15][16] which show that only approximately 20-30% of emitted photons escape a noncavity planar OLED fabricated on a conventional glass substrate. [17][18][19] Hence, in order to fully convert the input electrical power into optical power, it is essential to overcome this low outcoupling efficiency. 3 It should be noted that two factors are closely associated with typically low OLED outcoupling efficiency: the planarity of the device and refractive indices of the thin film stack.…”

White organic light-emitting diodes with 4 nm metal electrode

“…15 However, for white emission, light outcoupling needs to be optimized for all colors, and therefore, thinner Ag layers with high transmission over a broad wavelength regime are essential. [16][17][18] We have previously demonstrated that a wetting layer comprised of a few nanometers of gold (Au) enables formation of ultrathin Ag electrodes that show excellent performance as top-electrodes of white inverted and non-inverted top-emitting OLEDs, and top-illuminated organic solar cells. [19][20][21] However, the replacement of the ITO bottom anode by such composite ultrathin electrodes has not been studied before.…”