Stable and all solution processable quantum dot light-emitting diodes
Embodiments of the invention are directed to quantum dot light emitting diodes (QD-LEDs) where the electron injection and transport layer comprises inorganic nanoparticles (I-NPs). The use of I-NPs results in an improved QD-LED over those having a conventional organic based electron injection and transport layer and does not require chemical reaction to form the inorganic layer. In one embodiment of the invention the hole injection and transport layer can be metal oxide nanoparticles (MO-NPs) which allows the entire device to have the stability of an all inorganic system and permit formation of the QD-LED by a series of relatively inexpensive steps involving deposition of suspensions of nanoparticles and removing the suspending vehicle.
1. A quantum dot light emitting diode (QD-LED), comprising:
a light emitting layer comprising a plurality of quantum dots (QDs); and
a particulate electron injection and transport layer consisting of a plurality of ZnO nanoparticles wherein the ZnO nanoparticies have a diameter less than 5 nm.
2. The QD-LED of claim 1 , wherein said QDs comprise: Group II-VI compound semiconductor nanocrystals; Group III-V or IV-VI compound semiconductor nanocrystals; CuInSe 2 nanocrystals; metal oxide nanoparticles; core-shell structured nanocrystals; said semiconductor nanocrystals doped with rare earth elements or transition metal elements; or any combination thereof.
3. The QD-LED of claim 2 , wherein said Group II-VI compound semiconductor nanocrystals comprises CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, CdSTe, or any combination thereof.
4. The QD-LED of claim 2 , wherein said Group III-V or IV-VI compound semiconductor nanocrystals comprises GaP, GaAs, GaSb, InP InAs and InSb; PbS, PbSe, PbTe or any combination thereof.
5. The QD-LED of claim 2 , wherein said core-shell structured nanocrystals comprise CdSe/ZnSe, CdSe/ZnS, CdS/ZnSe, CdS/ZnS, ZnSe/ZnS,InP/ZnS ZnO/MgO, or any combination thereof.
6. The QD-LED of claim 2 , wherein said semiconductor nanocrystals doped with rare earth elements comprise Eu, Er, Tb, Tm, Dy or any combination thereof.
7. The QD-LED of claim 1 , wherein said QDs have a mean characteristic diameter of less than 5 nm.
8. The QD-LED of claim 1 , further comprising a low work function electrode and a transparent high work function electrode.
9. The QD-LED of claim 8 , further comprising a hole injection and transport layer comprising a plurality of metal oxide nanoparticles (MO-NPs).
10. The QD-LED of claim 9 , wherein said MO-NPs comprises NiO, MoO 3 , MoS 2 , Cr 2 O 3 and Bi 2 O 3 , p-type ZnO, p-type GaN, or any combination thereof.
11. The QD-LED of claim 9 , wherein said electron injection and transport layer is between said low work function electrode and said light emitting layer and said hole injection and transport layer is between said light emitting layer and said transparent high work function electrode.
12. The QD-LED of claim 9 , wherein said electron injection and transport layer is between said high work function transparent electrode and said light emitting layer and said hole injection and transport layer is between said light emitting layer and said low work function electrode.
13. The QD-LED of claim 8 , wherein said low work function electrode comprises: aluminum; magnesium; calcium; barium; or a thin layer of LiF, CsF, or Cs 2 CO 3 covered with aluminum.
14. The QD-LED of claim 8 , wherein said transparent high work function electrode comprises poly(3,4-ethylenedioxylenethiophene):polystyrene sulfonic acid (PEDOT:PSS) or polythienothiophene (PTT) doped with poly(perfluoroethylene-perfluoroethersulfonic acid) (PFFSA) on indium-tin-oxide (ITO).
15. The QD-LED of claim 8 , wherein said transparent high work function electrode comprises indium-tin-oxide (ITO), indium-zinc-oxide (IZO), zinc-tin-oxide (ZTO), copper-indium-oxide (CIO), copper-zinc-oxide (CZO), gallium-zinc-oxide (GZO), aluminum-zinc-oxide (AZO), or carbon nanotubes.
16. The QD-LED of claim 15 , wherein said transparent high work function electrode further comprises poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4-(N-(4-sec-butylphenyl)) diphenylamine)] (TFB), poly(N,N′-bis( 4 -butylphenyl)-N,N′-bis(phenyl)benzidine) (poly-TPD), or poly-n-vinylcarbazole (PVK).
17. A method of preparing a QD-LED comprising:
providing an electrode;
depositing a particulate electron injection and transport layer;
depositing a light emitting layer comprising a plurality of QDs;
depositing a hole injection and transport layer; and
capping said QD-LED with a counter electrode, wherein said steps of depositing comprise a non-reactive fluid deposition method and wherein said electron injection and transport layer consists of ZnO nanoparticles, wherein said ZnO nanoparticles have a diameter less than 5 nm.
18. The method of claim 17 , wherein said depositing an electron injection and transport layer comprises spin coating, printing, casting, or spraying a surface of said electrode or said light emitting layer with a suspension of said ZnO nanoparticles and removing a suspending vehicle from said deposited suspension of said ZnO nanoparticles.
19. The method of claim 17 , wherein said depositing a hole injection and transport layer comprises spin coating, printing, casting, or spraying a surface of said electrode or said light emitting layer with a suspension of MO-NPs and removing a suspending vehicle from said deposited suspension of MO-NPs.
20. The method of claim 19 , wherein said MO-NPs comprise NiO, MoO 3 , MoS 2 , Cr 2 O 3 and Bi 2 O 3 , p-type ZnO, p-type GaN, or any combination thereof.
21. The method of claim 17 , wherein said depositing a hole injection and transport layer comprises spin coating, printing, casting, or spraying a surface of said electrode or said light emitting layer with a solution of one or more inorganic materials and removing a solvent from said deposited solution of inorganic materials.
22. The method of claim 17 , wherein said depositing a hole injection and transport layer comprises chemical vapor deposition, sputtering, e-beam evaporation or vacuum deposition.
23. The method of claim 17 , wherein each of said depositing steps comprises spin coating, printing, casting, or spraying a solution or suspension and subsequently removing a solvent or suspending vehicle from said deposited solution or suspension.