Recombination zone shift in phosphorescent white organic light-emitting devices with single host structure of multi-emission layers

• We investigated the recombination zone shift in the white OLEDs.
• Single host structure of multi-emission layers was used for white OLEDs.
• The EL spectrum was strongly dependent on the electron transport layer.
• The recombination zone was determined by the carrier injection.
• High efficiency white OLED was obtained by optimizing the recombination zone.

We have investigated the recombination zone in the phosphorescent white organic light-emitting devices with single host structure of multi-emission layers. Blue, green, and orange-red phosphorescent emitters were doped into the separate layers of single host material for fabricating the white devices with multi-emission layers. The electroluminescence spectrum was substantially modified by the shift of the recombination zone that was dependent upon the thickness of the electron transport layer. We investigated the recombination zone shift in terms of electric field distribution and carrier injection. A maximum external quantum efficiency of 15.9% and a maximum power efficiency of 28.9 lm/W were achieved by optimizing the recombination zone.