Organic light emitting device with increased light out coupling
View Patent ↗The invention relates to an organic light-emitting device (OLED) comprising at least: a first electrode ( 102 ); a second electrode ( 105 ); an organic light emissive layer ( 104 ) arranged between said first electrode and said second electrode; and an organic charge transport layer ( 103 ) arranged between said first electrode and said emissive layer, wherein i) the charge transport layer is patterned or provided with a periodic surface structure on a surface of the charge transport layer facing the emissive layer, and/or ii) an alignment layer ( 406 ) which allows for charge transport to the emissive layer is provided between said charge transport layer and said emissive layer, which alignment layer promotes alignment of the optical dipoles of molecules of said light emissive layer towards a common preferred direction of the molecular axes. The use of the patterned or structured charge transport layer and/or the alignment layer provides improved light out coupling from the OLED layer stack, i.e. increased external quantum efficiency.
1. An organic light-emitting device (OLED) comprising at least:
a first electrode;
a second electrode;
an organic light emissive layer arranged between said first electrode and said second electrode; and
an organic charge transport layer arranged between said first electrode and said emissive layer, wherein
i) the charge transport layer is patterned, having a discontinuous pattern on a surface of the charge transport layer facing the emissive layer, the pattern including selected portions removed from an initial continuous layer via lithography or etching; and
ii) an alignment layer that provides charge transport to the emissive layer is provided between said charge transport layer and said emissive layer, wherein the alignment layer is treated to promote alignment of the optical dipoles of molecules of said light emissive layer towards a common preferred direction of the molecular axes.
2. An OLED according to claim 1 , wherein said alignment layer is provided between the charge transport layer and the emissive layer and in direct contact with both the charge transport layer and the emissive layer.
3. An OLED according to claim 1 , wherein the alignment layer comprises a monolayer.
4. An OLED according to claim 2 , wherein the pattern of the charge transport layer has period dimensions in the range of from 10 Å to 100 nm.
5. An OLED according to claim 1 , wherein the charge transport layer has a refractive index which is lower than the refractive indices of any other of said layers of the OLED.
6. An OLED according to claim 5 , wherein the charge transport layer forms a photonic crystal.
7. An OLED according to claim 5 , wherein the pattern of the charge transport layer has period dimensions in the range of from 1 nm to 100 μm.
8. An OLED according to claim 5 , wherein the pattern of the charge transport layer has period dimensions in the range of from 1 nm to 1 μm.
9. An OLED according to claim 6 , wherein the optical density of states of the photonic crystal in the in-plane direction is suppressed by the charge transport layer being patterned, and/or the optical density of states in directions with angles smaller than the critical angle of total internal reflection (θc), defined with respect to the layer normal, is enhanced by the charge transport layer being patterned.
10. An OLED according to claim 1 , wherein at least one of said layers is solution processed.
11. An OLED according to claim 10 , wherein at least the charge transport layer is solution processed.
12. An OLED according to claim 1 , wherein the alignment layer is treated by rubbing or by photo irradiation to promote alignment of the optical dipoles of molecules of said light emissive layer towards the common preferred direction of the molecular axes.