New emission band of PtOEP phosphor in organic LED devices

Electroluminescence (EL) and transient EL response have been studied on organic light-emitting diode (OLED) devices based on phosphorescent PtOEP molecule. As the emitting layer, we used layer of PtOEP doped in CBP host material and layer formed by 100%PtOEP (without doping in host). Three EL bands are observed at 500, 527 and 570 nm in the latter device besides red EL due to PtOEP. The 500 and 527 nm ELs are attributed to emission from hole- and electron-transport layers, respectively, while the 570 nm EL to emission from exciplex formed at the interface between the hole-blocking layer and emitting layer. Weak emission from the thermally populated triplet state is observed in single layer OLED device with 100%PtOEP layer and multi-layer device with PtOEP doped in host. Double exponential decay is observed in the electrophoresecence in the 100%PtOEP layer device, while a single exponential decay is observed in the device with PtOEP doped in host.