Light-emitting device including quantum dots
A light emitting device including an emissive material comprising quantum dots is disclosed. In one embodiment, the device includes a cathode, a layer comprising a material capable of transporting and injection electrons comprising an inorganic material, an emissive layer comprising quantum dots, a layer comprising a material capable of transporting holes, a layer comprising a hole injection material, and an anode. In certain embodiments, the hole injection material can be a p-type doped hole transport material. In certain preferred embodiments, quantum dots comprise semiconductor nanocrystals. In another aspect of the invention, there is provided a light emitting device wherein the device has an initial turn-on voltage that is not greater than 1240/λ, wherein λ represents the wavelength (nm) of light emitted by the emissive layer. Other light emitting devices and a method are disclosed.
1. A light emitting device including:
a pair of electrodes comprising
an anode, and
a cathode, wherein at least one of the anode and the cathode comprises indium tin oxide;
a layer comprising a light emissive material comprising quantum dots provided between the electrodes;
a layer comprising an inorganic material provided between the emissive layer and the cathode;
a layer comprising a hole transporting material provided between the emissive layer and the anode; and
a layer comprising a hole-injection material provided between the anode and the layer comprising the hole transporting material,
wherein the inorganic material comprises a crystalline zinc oxide,
wherein the layer comprising the inorganic material comprises a stratified structure including three or more horizontal zones having different conductivities from each other, and
wherein the three or more horizontal zones comprise,
a first zone at an upper portion of the layer nearer the emissive layer, the first zone comprising a hole blocking material,
a third zone at a lower portion of the layer more remote from the emissive layer, the third zone comprising an electron injecting material, and
a second zone between the first zone and the third zone, the second zone comprising an electron transporting material,
wherein the hole blocking material comprises an intrinsic inorganic material,
the electron injecting material comprises a first slightly n-doped inorganic material, and
the electron transporting material comprises a second slightly n-doped inorganic material having a lower concentration of n-type doping than the first slightly n-doped inorganic material.
2. A light emitting device in accordance with claim 1 wherein the inorganic material included in each of the first zone, the second zone, and the third zones of the stratified structure can be doped or undoped forms of the same or different materials.
3. A light emitting device in accordance with claim 2 wherein electron and hole populations are balanced at the emissive layer of the device.
4. A light emitting device in accordance with claim 1 wherein the inorganic material comprises a metal chalcogenide.
5. A light emitting device in accordance with claim 1 wherein the inorganic material comprises a metal oxide.
6. A light emitting device in accordance with claim 1 wherein the inorganic material comprises zinc oxide.
7. A light emitting device in accordance with claim 6 wherein the zinc oxide is surface treated with an oxidizing agent to render a surface proximate to the emissive layer intrinsic.
8. A light emitting device in accordance with claim 1 wherein the inorganic material comprises a mixture of two or more inorganic materials.
9. A light emitting device in accordance with claim 1 wherein the inorganic material comprises an inorganic semiconductor material.
10. A light emitting device according to claim 1 , wherein the cathode comprises indium tin oxide.
11. A light emitting device in accordance with claim 1 wherein the third zone comprises an n-type doped zinc oxide, the second zone comprises an n-type doped zinc oxide having a lower n-type dopant concentration than that of the zinc oxide in the third zone, and the first zone comprises intrinsic zinc oxide.
12. A light emitting device in accordance with claim 1 wherein the inorganic material comprises a mixture of the crystalline zinc oxide and a titanium oxide.
13. A light emitting device in accordance with claim 1 , wherein the hole transporting material comprises a first organic material and the hole injection material comprises a second organic material different from the first organic material or an inorganic material.