Efficient non-doped monochrome and white phosphorescent organic light-emitting diodes based on ultrathin emissive layers

•We successfully demonstrated efficient non-doped OLEDs with simplified device structure.•We also discussed the working mechanism of the OLEDs based on ultrathin emissive layers.•The designed white device showed very stable spectra and higher power efficiency than the control one.•The effect of the ultrathin layer thickness on the performance of OLEDs was investigated.