Organic Light-Emitting Diodes (OLEDs) are a novel platform device emerging in the bio/medical field. Research on OLED as a future device has been conducted to overcome the disadvantages of Light-Emitting Diodes (LEDs) and laser light sources. The skin penetration depth of any light is determined by the scattering and absorption coefficients of human tissue. Light can penetrate deep into the skin at red wavelength above. In particular, OLEDs with Near Infra-Red (NIR) wavelengths are expected to be more effective for pain relief and pain treatment. However, it is difficult to fabricate NIR emitters because, according to the law of energy band gap, the nonradiative rate increases as the energy gap between HOMO and LUMO decreases. Therefore, research has been performed on NIR OLEDs that can be applied in various ways in the bio/medical field. NIR OLEDs fabricated using solution process have an unfavorably broad Full Width Half Maximum (FWHM), insufficient radiant emittance for application to phototherapy, and an undetermined life span. NIR OLEDs produced by synthesizing NIR emitter also have limitations such as broad FWHM and unstable lifetime. Moreover, with these latter devices it is impossible to control the wavelength.

In this study, using the micro-cavity tandem structure shown in Fig. 1(a, b), we fabricate highly reliable NIR OLEDs with narrow FWHM (34 nm) and sufficient radiant emittance (6.64 mW/cm2). The important Charge Generation Layer (CGL), which supplies electric charge to adjacent emitting layers, is composed of an n-type ETL and p-type metal oxide. Li-based compound was used as n-type dopant, and MoO3 was used as p-type metal oxide.

Finally, we confirm the cell proliferation effect by irradiating NIR OLEDs, with results shown in Fig.1(c), and show that devices can be applied to various areas in the bio/medical field.