OLEDs are considered to be particularly suitable for wearable devices or human contact devices. They can be processed at low temperature on various flexible substrates, such as plastics, which are very useful for light sources such as goose feather, flexible, stretchable and conformal objects. In fact, most of the display devices used in smart watch wearable devices are plastic active matrix OLED because of its light and thin appearance. The application of OLEDs in wearable devices is not limited to the display screen of smart watch. In fact, OLEDs can also play an important role in the field of mobile medicine, especially in the form of wearable devices. For example, health monitoring sensors measure important human signals, such as heart rate and blood oxygen levels, as well as light patches for advanced wound care or skin care, as shown in Figure 1. Here we will review the highlights and key issues of these OLEDs in wearable healthcare applications.

OLEDs for wearable pulse oximetry sensor

Cardiovascular circulation is the most important biological activity to maintain life. Therefore, it is very important to monitor it in an appropriate way. In many cases, measurement of these activities is limited to in-hospital care, but it is rapidly expanding to mobile or personal health care. In particular, the progress of wearable electronic devices makes it possible to measure daily activities from health tracking to biological signal monitoring of infants, patients with chronic diseases or discharged patients after surgery. In cardiovascular monitoring methods, photoplethysmography (PPG) signal and blood oxygen saturation (SpO2) levels are measured noninvasively by using light-emitting devices and photodetectors. Organic light emitting diodes (OLEDs) and organic photodiodes (OPDS) can be used as light sources and detectors for wearable PPG and / or SpO2 sensors due to their good compatibility with wearable or human body attached form factors. At present, some research groups have proved that OLED technology is a feasible and promising wearable health monitoring technology.

Wearable OLED patch for advanced wound care

Photobiomodulation (PBM) refers to the biological changes caused by the interaction of molecules in cells or tissues with light. The therapeutic effect of PBM has been discovered in ancient times, but it has become popular recently with the development of various light sources such as laser and led. For example, photons absorbed by chromophores known as cytochrome c oxidase can lead to luminescent chemical reactions, promote the synthesis of adenosine triphosphate, and provide energy for various processes in the organism. This process can help cells grow more efficiently, thus allowing tissue damage to heal faster. So far, these phototherapies have installed light sources in hospitals, which often limits the frequency and duration of PBM treatment per patient. In this sense, OLEDs are very useful in a wearable, patched form because they can be used for personal healthcare. Even in a hospital setting, a deep trauma patient does not need to move to the location of the PBM light source; instead, the patient can apply a PBM patch to the wound in his or her bed, just like a bandage. As a kind of area light source, OLED is considered to be very beneficial. It produces uniform light output without producing too much heat, which is very important to prevent heat damage to cells and tissues.


After realizing this potential, people have made great efforts to develop OLED based phototherapy technology, and proposed a PBM device based on OLED (Fig. 5a-c). As a surface light source, OLED can produce uniform light output at 10 mW cm − 2 irradiance. Effective wavelength tuning can be achieved through microcavity effect.