Abstract
A recent and emerging application of organic light emitting diodes (OLEDs) is in wearable technologies as they are flexible, stretchable and have uniform illumination over a large area. In such applications, transmission of OLED emission through skin is an important part and therefore, understanding spectral changes associated with transmission of OLED emission through human skin is crucial. Here, we report results on transmission of OLED emission through human skin samples for yellow and red emitting OLEDs. We found that the intensity of transmitted light varies depending on the site from where the skin samples are taken. Additionally, we show that the amount of transmitted light reduces by ~ 35–40% when edge emissions from the OLEDs are blocked by a mask exposing only the light emitting area of the OLED. Further, the emission/electroluminescence spectra of the OLEDs widen significantly upon passing through skin and the full width at half maximum increases by >20 nm and >15 nm for yellow and red OLEDs, respectively. For comparison, emission profile and intensities of transmitted light for yellow and red inorganic LEDs are also presented. Our results are highly relevant for the rapidly expanding area of non-invasive wearable technologies that use organic optoelectronic devices for sensing.
Highlights
Applications of organic light emitting diodes (OLEDs) in wearable technology are mainly as a light source where emission from an OLED needs to penetrate past the skin barrier[1,2]
The EL of both yellow and red OLEDs has a full width half maximum (FWHM) of around 90 nm, which is typical of fluorescent OLEDs15,16
The ELs of yellow flat (YF) and yellow round (YR) LEDs are almost exactly the same, whereas EL of red round (RR) LED is red-shifted as compared to red flat (RF) LED
Summary
Applications of OLEDs in wearable technology are mainly as a light source where emission from an OLED needs to penetrate past the skin barrier[1,2]. Accurate measurements have been reported for cutaneous sensors with OLEDs, such as pulse oximetry. Such applications require OLED light to penetrate the skin, which is a highly inhomogeneous medium with a very complex multi-layered structure. Light from OLEDs are highly incoherent and non-monochromatic, and OLEDs have a wide electroluminescence (EL) spectrum. We describe the changes in intensity and EL spectrum of emission from yellow and red OLEDs when it penetrates human skin. These results provide guidelines for the application of OLEDs in wearable technologies
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