The doped-free structure is used to realize organic light-emitting devices with low blue harm, low color temperature and high color rendering index

With the development of light-emitting devices, researcher gradually shift their attention from the efficiency of the devices to the health of lighting sources. Herein, we first designed a low correlated color temperature (CCT) and high color rendering index (CRI) spectrum with minimal blue light accession, which is beneficial to reduce the inhibitory effect of melatonin secretion. Besides, the spectrum had suitable near-infrared light with a wavelength of 670-810 nm, which could promote cellular metabolism, migration, and value-added, achieving more comfortable and healthy lighting. To meet the requirement of this spectrum, an organic light-emitting device (OLED) was prepared through the construction of a tri-layered structure, to which the ultrathin emitting layers (UEMLs) position between TCTA and TmPyPB. By controlling the thickness of these phosphorescent UEMLs, the ratio of emission peaks of UEMLs were modulated precisely, and the device showed a CRI of 91.7 at a low CCT of 1850K, a maximum current efficiency (CE) of 38.4 cd/A and a power efficiency (PE) of 24.3 lm/W. This study provided a simple and low-cost preparation strategy for OLED with low CCT and high CRI and provided a powerful reference for the construction of healthy near-eye display devices and indoor light sources.