Hitachi Research Laboratory (HRL) of Hitachi Ltd exhibited a prototype of an OLED lighting panel made by using a coating process at Lighting Fair 2013, a trade show on lighting technologies, which runs from March 5 to 8, 2013, in Tokyo.
For the panel, HRL used the "spontaneous multilayer light-emitting layer formation material," which enables to make an OLED lighting panel just by applying HRL's own red (R), green (G) and blue (B) light-emitting materials once.
In general, white OLED lighting panels made by using a coating process are made by applying RGB light-emitting materials in three or more stages to form RGB light-emitting layers. However, in this process, upper layers react with lower layers, destroying the layer structure.
On the other hand, with the spontaneous multilayer light-emitting layer formation material, after mixing together the RGB light-emitting materials (dopants) consisting of low-molecular materials and applying it once, green, blue and red layers are automatically formed in this order from bottom up because of the effect of self-organization.
As a host material, the same wide band-gap material is used for the RGB dopants. The prototyped OLED panel with a light-extraction layer emits light with a luminous efficiency of up to 70lm/W.