Polymer buffer layers and their use in light-emitting diodes
View Patent ↗The present invention is directed to improved transparent electrically conductive buffer layers for light-emitting diodes. The use of an aqueous dispersion containing an electrically conducting polymer and a non-ionic surfactant or an ionic fluorosurfactant to form the buffer layer has been shown to provide a buffer layer that results in improved light-emitting diode performance.
1. A light-emitting device on a substrate, said light-emitting device comprising:
(a) an anode;
(b) a cathode;
(c) an active emission layer positioned between said anode and said cathode; and
(d) a buffer layer positioned between said anode and said active emission layer, wherein said buffer layer is comprised of an electrically conducting polymer and a surfactant, the amount of said surfactant is from about 0.5 wt % to about 15 wt % of the total weight of said surfactant and said electrically conducting polymer, and said surfactant is a fluorosurfactant or a polyoxyethylene alkylphenol ether.
2. The device of claim 1 , wherein said surfactant is a non-ionic surfactant.
3. The device of claim 2 , wherein said non-ionic surfactant is a fluorosurfactant.
4. The device of claim 3 , wherein said fluorosurfactant contains a perfluoroalkyl group with the formula F(CF 2 CF 2 ) 3-8 .
5. The device of claim 4 , wherein said fluorosurfactant is a perfluoroalkylpolyoxyethylene.
6. The device of claim 3 , wherein said fluorosurfactant is comprised of a fluoroaliphatic polymeric ester.
7. The device of claim 2 , wherein said non-ionic surfactant is a polyoxyethlyene alkylphenol ether.
8. The device of claim 7 , wherein said polyoxyethlyene alkylphenol ether is polyoxyethylene (10) isooctylphenyl ether.
9. The device of claim 1 wherein said fluorosurfactant is an ionic fluorosurfactant.
10. The device of claim 1 , wherein the amount of said surfactant is from about 1 wt % to about 10 wt % of the total weight of said surfactant and said electrically conducting polymer.
11. The device of claim 1 , wherein said electrically conducting polymer is a polyaniline.
12. The device of claim 1 , wherein said electrically conducting polymer is a poly(dioxythiopene).
13. The device of claim 12 , wherein said poly(dioxythiopene) is poly(3,4-ethylenedioxythiophene).
14. The device of claim 1 , wherein said anode is comprised of at least one bilayer comprised of a metal layer and a dielectric layer and wherein at least one of said dielectric layer is adjacent to said buffer layer.
15. The device of claim 14 , wherein at least one of said dielectric layer disposed adjacent to said buffer layer is disposed directly on said buffer layer.
16. A light-emitting device on a substrate, said light-emitting device comprising:
(a) an anode;
(b) a cathode;
(c) an active emission layer positioned between said anode and said cathode; and
(d) a buffer layer positioned between said anode and said active emission layer, wherein said buffer layer is formed using an aqueous dispersion of an electrically conducting polymer to which has been added a surfactant, said dispersion is characterized by a surface tension of between 25 and 35 mN/M, the concentration of said electrically conducting polymer is from 0.1 to 5.0% w/w of said electrically conducting polymer in said dispersion, the concentration of said surfactant is less than about 0.4% w/w of said surfactant in said dispersion, and said surfactant is a fluorosurfactant or a polyoxyethylene alkylphenol ether.
17. The device of claim 16 , wherein said surfactant is a non-ionic surfactant.
18. The device of claim 17 , wherein said non-ionic surfactant is a fluorosurfactant.
19. The device of claim 18 , wherein said fluorosurfactant contains a perfluoroalkyl group with the formula F(CF 2 CF 2 ) 3-8 .
20. The device of claim 19 , wherein said fluorosurfactant is a perfluoroalkylpolyoxyethylene.
21. The device of claim 18 , wherein said fluorosurfactant is comprised of a fluoroaliphatic polymeric ester.
22. The device of claim 17 , wherein said non-ionic surfactant is a polyoxyethlyene alkylphenol ether.
23. The device of claim 22 , wherein said polyoxyethlyene alkylphenol ether is polyoxyethylene (10) isooctylphenyl ether.
24. The device of claim 16 , wherein said concentration of said electrically conducting polymer is from 0.1 to 5.0% w/w of said electrically conducting polymer in said dispersion and said concentration of said surfactant is less than about 0.3% w/w of said surfactant in said dispersion.
25. The device of claim 16 , wherein said electrically conducting polymer is a polyaniline.
26. The device of claim 16 , wherein said electrically conducting polymer is a poly(dioxythiopene).
27. The device of claim 26 , wherein said poly(dioxythiopene) is poly(3,4-ethylenedioxythiophene).
28. The device of claim 16 , wherein said anode is comprised of indium tin oxide.
29. The device of claim 16 , wherein said anode is comprised of at least one bilayer, each of the at least one bilayer comprising a metal layer and a dielectric layer, wherein at least one of said dielectric layer is adjacent to said buffer layer.
30. The device of claim 29 , wherein at least one of said dielectric layer disposed adjacent to said buffer layer is disposed directly on said buffer layer.