Cascaded organic electroluminescent device having connecting units with N-type and P-type organic layers
View Patent ↗A cascaded organic electroluminescent device includes an anode and a cathode. The device also includes a plurality of organic electroluminescent units disposed between the anode and the cathode, wherein the organic electroluminescent units comprise at least a hole-transporting layer, an electron-transporting layer, and an electroluminescent zone formed between the hole-transporting layer and the electron-transporting layer wherein the physical spacing between adjacent electroluminescent zones is more than 90 nm; and a connecting unit disposed between each adjacent organic electroluminescent unit, wherein the connecting unit comprises, in sequence, an n-type doped organic layer and a p-type doped organic layer forming a transparent p-n junction structure wherein the resistivity of each of the doped layers is higher than 10 Ω-cm.
1. A cascaded organic electroluminescent device comprising:
a) an anode;
b) a cathode;
c) a plurality of organic electroluminescent units disposed between the anode and the cathode, wherein the organic electroluminescent units comprise at least a hole-transporting layer, an electron-transporting layer, and an electroluminescent zone formed between the hole-transporting layer and the electron-transporting layer wherein the physical spacing between adjacent electroluminescent zones is more than 90 nm; and
d) a connecting unit disposed between each adjacent organic electroluminescent unit, wherein the connecting unit comprises, in sequence, an n-type doped organic layer and a p-type doped organic layer forming a transparent p-n junction structure wherein the resistivity of each of the doped layers is higher than 10 Ω-cm.
2. The cascaded organic electroluminescent device of claim 1 wherein each connecting unit has at least a 90% optical transmission in the visible region of the spectrum.
3. The cascaded organic electroluminescent device of claim 1 wherein the thickness of each connecting unit is in a range of from 1 to 400 nm.
4. The connecting unit of claim 1 wherein the thickness ratio between the n-type doped organic and the p-type doped organic layer is in a range of from 1:10 to 10:1.
5. The cascaded organic electroluminescent device of claim 1 wherein the anode or cathode is a reflective electrode and the optical distance from the electroluminescent zone of each organic electroluminescent unit to the reflective electrode is selected in the range from 0.8×[(2m+1)×(λ/4)] to 1.2×[(2m+1)×(λ/4)], wherein m is an integer of 0, 1, 2, 3, or larger, and λ is the peak emission wavelength of the electroluminescent unit.
6. The cascaded organic electroluminescent device of claim 1 wherein anode or cathode is a reflective electrode and the optical distance from the electroluminescent zone of each organic electroluminescent unit to the reflective electrode is selected as [(2m+η)×(λ/4)] so that the light extraction can be optimized, wherein m is an integer of 0, 1, 2, 3, or larger, η is a coefficient selected in the range of from 0.6 to 1.0, and λ is the peak emission wavelength of the electroluminescent unit.
7. The cascaded organic electroluminescent device of claim 1 wherein anode or cathode is a reflective electrode and the physical spacing between the electroluminescent zone of each organic electroluminescent unit and the reflective electrode is selected in accordance with the corresponding optical distance.
8. The cascaded organic electroluminescent device of claim 1 wherein the physical spacing between each electroluminescent zone of the electroluminescent units is selected to improve the light extraction from the electroluminescent device.
9. The cascaded organic electroluminescent device of claim 1 wherein anode or cathode is a reflective electrode and the physical spacing from the electroluminescent zone of each organic electroluminescent unit to the reflective electrode is adjusted by changing the thickness of the connecting unit.
10. The cascaded organic electroluminescent device of claim 1 wherein anode or cathode is a reflective electrode and the physical spacing from the electroluminescent zone of each organic electroluminescent unit to the reflective electrode is adjusted by choosing the host materials of the connecting unit with suitable refraction indexes.