WO2008154915A1

WO2008154915A1 - Use of a metal complex as a p-dopant for an organic semiconductive matrix material, organic semiconductor material, and electronic component

Info

Publication number: WO2008154915A1
Application number: PCT/DE2008/001034
Authority: WO
Inventors: Günter Schmid; Ralf Krause
Original assignee: Osram Opto Semiconductors Gmbh
Priority date: 2007-06-20
Filing date: 2008-06-18
Publication date: 2008-12-24
Also published as: DE102007028237A1

Abstract

The invention relates to the use of a dirhodium metal complex as a p-dopant for an organic semiconductive matrix material, an organic semiconductor material, and an organic electronic component. The invention describes the use of metal complexes acting as Lewis acids as p-dopants in organic matrix materials.

Description

description

USE OF METAL COMPLEX AS P-DOTAND

FOR AN ORGANIC SEMICONDUCTOR MATRIX MATERIAL, ORGANIC

SEMICONDUCTOR MATERIAL AND ELECTRONIC COMPONENT

The invention relates to the use of a metal complex as p-dopant for an organic semiconductive matrix material, an organic semiconductor material and electronic component.

The doping of organic semiconducting materials with electron acceptors for increasing the conductivity in organic matrix materials is known, for example, from WO 2005/086251. There, metal complexes, in particular polynuclear metal complexes such as the paddle-wheel complexes, are described as n-dopants for electron injection because of their strong donor properties.

However, there is a need to provide p-dopants for doping the hole injection layer.

The object of the present invention is therefore to provide p-dopants for a hole-conducting matrix and to disclose the uses of such doped hole-conducting matrix materials in an organic electronic component.

This object is achieved by the features of the independent claims, in particular by the use of neutral metal complexes with Lewis acid character as p-dopants in hole-conducting organic matrix materials. Furthermore, the object is achieved by the provision of an organic semiconductive material with a compound of such a metal complex with Lewis acid character as p-dopant. Finally, the object is achieved by providing organic electronic components with at least one layer of an organic matrix material according to the invention. The invention relates to the use of a neutral metal complex having Lewis acid properties as a p-type dopant of an organic semiconductive matrix material. The invention further provides a hole conductor layer consisting of a hole-conducting organic matrix material with a proportion of 0.1 to 50 (layer thickness%) of metal complex as p-dopant. Finally, the subject matter of the invention is an organic electronic semiconductor component comprising at least one layer of a doped hole conductor material which contains a metal complex as p-dopant.

Lewis acids are compounds that act as electron pair acceptors. A Lewis base is accordingly an electron pair donor that can donate electron pairs. In particular, the Lewis acid property of the metal complexes has to be set with respect to the hole-conducting organic matrix material, which then represents (or contains) the corresponding Lewis base.

A metal complex is a compound in which a metal atom or metal ion is coordinated by one or more ligands. As a rule, the metal complex is an organometallic compound, that is, a complex in which at least some of the ligands are carbon-containing and often also hydrocarbon-containing.

Advantageously, the metal complex is a polynuclear complex, in particular a complex with at least one metal-metal bond.

According to an advantageous embodiment, at least one central atom of the metal complex is selected from the group of platinum metals, comprising the following elements: ruthenium, rhodium, palladium, osmium, iridium and platinum. In particular, rhodium complexes are preferred. According to an advantageous embodiment, the central atom is a neutral or charged, in particular positively charged, transition metal atom.

Among hole conductors, the typical materials which are hole-conducting in an organic electronic semiconductor device, such as NPB (N ₇ N'-di-1-naphthyl-diphenylbenzidine, HOMO = 5.5 eV, LUMO = 2.4 eV) or naphdata (4 , 4 ', 4 "-Tris (N- (1-naphthyl) -N-phenyl-amino) -triphenylamine, - HOMO = 5.1 eV, LUMO = 2.3 eV) understood.

The doping will be given below in relative layer thicknesses, i. x% means that the deposition rate of the donor is x% with respect to the deposition rate of the matrix.

Advantageously, a complex with a so-called "paddle-wheel / paddle wheel" structure is used as the neutral metal complex, particularly preferably bi- and polynuclear metal complexes having at least one metal-metal structure.

Binding, such as, for example, Cotton FA, Gruhn NE, Gu J, Huang P, Lichtenberger DL, Murillo Ca, Van Dorn LO and Wilkinson CC: "Closed Shell Molecules That Ionize Readily More Than Cesium" in Science, 2002, 298, 1971- 1974. These structures are also described in WO 2005/086251, where it is assumed, however, that multinuclear metal complexes with a paddle wheel structure act as "n-dopants", but this does not apply to all paddle wheels. Wheel complexes or the structures mentioned there, as could be shown in the present case.

In WO 2005/086251 A2 complexes with paddle wheel structure are presented as typical n-dopants. To investigate the utility of dirhodium tetra-trifluoroacetate (PDW-2), a typical representative of the strong Lewis metal complexes.

Acid character as present as p-dopants below Protection to be verified as n-dopant, the following experiment was performed:

On a ITO (indium-tin-oxide = indium-doped tin oxide) electrode, a 150 nm thick layer of the electron conductor BCP (= 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenantholin) was deposited by thermal evaporation. The exposed electrode was a 150 nm thick aluminum layer. FIG. 1 shows the result, with a 4 mm ² component being measured, which yielded the characteristic curve marked by squares (FIG. 1, squares).

In a second experiment 10% PDW-2 is doped into the BCP layer by co-evaporation. The characteristic marked by circles in FIG. 1 differs only insignificantly from the characteristic curve of the pure BCP. Thus, PDW-2 is generally not usable as n-dopant, in particular not in an organic electronic semiconductor device and the typical electronic conductors used therein with a typical HOMO in the range 5.8 - 6.2 eV or a typical LUMO in the range of 3, 0-2.4 eV.

Analogously to the experiment described above, PDW-2 is by coevaporation in the hole ladder NPB (= bis-N, N, N ', N' - (naphthyl-phenyl) benzidine) doped. For a doping of 0% (circles full), 1% (squares), 5% (triangles) and 10% (circles empty), the curves shown in Figure 2 were obtained.

These clearly demonstrate the potential for p-doping of hole-conducting matrix materials by PDW-2. Surprisingly, can be injected (negative branch of the x-axis), whereby a rectification factor of 3-10 ^"7 yields of aluminum no holes for effective doping just relative layer thicknesses range% from (particularly 0 -. 50%, particularly preferably 0 The characteristic curves between 1 - 10% PDW-2 in NPB are almost identical and the characteristics are also very steep, saturating at higher voltages the characteristic, which results in a current-limiting behavior.

The doping of organic matrix materials with p-dopants is of crucial relevance for organic electronic components. Doped transport layers have the advantage that only a fraction of the voltage required for operation drops in them relative to the overall structure (<< 30%). Particularly preferably, the falling voltage is even smaller by a power of ten or more, so that no voltage drop is observed at the transport layers.

FIG. 3 shows an example of a layer structure of a photodetector.

The structure is shown in the form of a stack consisting of top electrode 5, bottom electrode 3, the carrier substrate 1 and the organic photodiode layer 4 and the hole-guiding layer 6.

An example of the construction of an organic photodetector having two active organic layers 4 and 6 can be seen. The layer 6 shows the p-doped hole transporter according to the invention. The actual photoconductive layer is designated by the reference numeral 4. In addition to the layers 5, 3, 1, 4 and 6 shown, the protection of the photodetector by means of encapsulation is also expedient.

The bottom electrode 3 (anode) can be made of indium tin oxide (ITO) or of another metal. The top electrode 5 (cathode) may consist of aluminum (Al) or for example also of a Ca / Ag layer system or also of LiF / Al.

Via the electrical line 7, the electrodes are connected to the voltage source. In the case of large-area photodiodes, the homogeneity of the charge injection plays an important role. Particles, crystallites or tips cause field elevations and thus potential starting points for "dark spots" which can lead to failure of the diode, through a hole injection layer or hole transport layer 6 in which, for example, dinuclear rhodium acetate-based paddle-wheel complexes are embedded. For example, a layer can be produced which exhibits an unexpectedly high current carrying capacity in conjunction with an inherent current limitation.

Rhodium complexes are preferably used, such as metal complex compounds having a Rh ₂ ⁴⁺ core and a metal-metal bond, which act as p-dopant and electron acceptor due to their high Lewis acid character.

Particularly preferred is the dirhodium tetratrifluoroacetate (Figure 4), which is very well suited due to its favorable sublimation properties. The Chemical Literature [FA Cotton, CA Murillo, RA Walton's "Multiple Bonds between Metal Atoms" 3rd Edition, Springer Science and Business Media, Inc. 2005. 465-611.] Could also be shown, crystallographically, that even unsubstituted - Can serve as aromatic donor for the Rh ₂ ⁴⁺ core in the axial position. Experimentally, by doping NPB or naphdata (Naphdata = 4,4 ', 4 "-tris ((N-naphthyl) -N-phenyl-amino) -triphenylamine) with PDW-2 in experiments described above, it could be shown that this Operation causes a p-doping.

Figure 4 shows the structure of Rh ₂ (CF ₃ COO) ₄ , to which the aromatic system hexamethylbenzene is coordinated.

The metal complexes that are isoelectronic with Rh ₂ ⁴⁺ complexes to this structure, especially those that are still similar

Sizes such as an analogue with Ru ₂ ²⁺ ions as central atoms are also suitable as p-dopants. These effect on the one hand the Schaufelradstruktur and on the other the very high Lewis acidity of these complexes. , Particularly suitable are the central atoms or metal complexes suitable as p-dopants, which can coordinate directly to aromatic systems, such as, for example, uncharged aromatic systems. As central atoms, therefore, especially the metals of the 6th to 9th subgroup are considered

In a paddle-wheel complex, at least two, usually exactly two, metal central atoms, in particular transition metal atoms, are bridged by 1, 2, 3, 4 or more multidentate (in particular bidentate) ligands which each bind a ligand atom to the at least two metal central atoms. The metal atoms are here, depending on the radius, usually 4 times coordinated with the mentioned ligands. The Lewis acid character of the paddle-wheel complexes is given in particular by the presence of a loose or empty coordination site on at least one metal atom, at which, for example, the attachment of an aromatic ring can take place, as shown in FIG. The coordination environment of the metal atom is preferably such that there is a metal-metal bond and 4 equatorial bonds to ligands. As a rule, therefore, the axial position has the loose or empty coordination point, whereby the complex is Lewis acid depending on the ligand and central atom.

Suitable ligands are in particular all two or more dentate ligands, preferably electron-withdrawing ligands. Examples which may be mentioned are the anions of electron-withdrawing carboxylic acids, such as, for example, CH aI _x H ₃ . _{X is} COOH, and in particular CF _X H ₃ - _X COOH and CC1 _X H ₃ _ _X COOH (wherein x and Hal is an integer between 0 and 3 represents a halogen atom), (CRi, R _2, R ₃₎ COOH, where R 1, R ₂ and R _3, independently of one another, are alkyl, particularly preferably H, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, and also benzoic acid and its substituted analogs (o, p, m-fluorobenzoic acid, o, p, m-cyanobenzoic acid, nitrobenzoic acid, alkylbenzoic acids with fluorinated or partially fluorinated alkyl groups, if appropriate may also be monosubstituted or polysubstituted, pyridinecarboxylic acids, etc.).

The metal complexes used in accordance with the invention are preferably molecules which can be vaporized independently of one another. It is understood that individual metal complexes may each be bonded to each other or to other components such as the matrix material.

In purely formal terms, the valence electrons of PDW-2 could be calculated as follows:

In group IX with 4 single negatively charged bidentate

Ligands gives the following picture for metal-metal:

4 x 4e = 16 electrons from the ligands 1 x 2e = 2 from the single bond between Rh-Rh

2 x 9e = 18 of rhodium

Sum 36, so that each Rh has noble gas configuration, i. stable

Alternatively, the sum of 36 for other metals equals the same ligands: Group 6 metals: metal - metal quadruple bond, i. σ,

2 x π, I x δ bond occupied

Group 7 metals: metal - metal triple bond i. σ,

2 x π, I x δ bond, 1 x δ * occupied

Group 8 metals: metal - metal double bond i. σ, 2 x π, 1 x δ bond, 1 x δ *, 1 x π * occupied

Group 9 metals: metal - metal single bond i. σ,

2 x π, I x δ bond, 1 x δ *, 2 x π * occupied

It is understood that individual metal complexes can each be bound together or with other components such as the matrix material. By binding form the donor Akzeptorwechselwirkung and ^■ the molecular size of the dopants are fixed in the matrix.

Suitable organic matrix materials are all common hole conductor matrices, such as NPB; NaphDATA; N, N ¹ -bis (naphthalen-1-yl) -N, N ¹ -bis (phenyl) -benzidines; N, N ¹ - bis (naphthalen-2-yl) -N, N '-bis (phenyl) -benzidines; N, N ^! -To 3- methylphenyl) -N, N ¹ -bis (phenyl) -benzidines; N, N'-bis (3-methylphenyl) -N, N ¹ -bis (phenyl) -9,9-spirobifluorene; N, N '- bis (naphthalen-1-yl) -N, N' -bis (phenyl) -9,9-spirobifluorenes; N, N'-bis (3-methylphenyl) -N, N ¹ -bis (phenyl) -9,9-dimethylfluorenes; N, N ¹ -bis (3-naphthalen-1-yl) -N, N ¹ -bis (phenyl) -9,9-dimethyl-fluorenes; N, N ¹ -bis (3-methylphenyl) -N, N ¹ -bis (phenyl) -9,9-diphenyl-fluorenes; N, N ¹ -bis (3-naphthalen-1-yl) -N, N ¹ -bis (phenyl) -9,9-diphenyl-fluorenes; 2, 2 ', 7, 7' tetrakis (N, N-diphenylamino) -9,9'-spirobifluorenes; 9,9-bis [4- (N, N-bis-biphenyl-4-yl-amino) -phenyl] -9H-fluorenes; 9,9-bis [4- (N, N-bis-naphthalen-2-ylamino) -phenyl] -9H-fluorenes; 9,9-bis [4- (N, N- ¹ -bis-naphthalen-2-yl-N, N'-bis-phenyl-amino) -phenyl] -9H-fluorenes; 2, 2 ', 7, 7' tetrakis [(N-naphthalenyl (phenyl) amino] - 9, 9-spirobifluorene; N, N ¹ -bis (phenanthren-9-yl) -N, N ¹ - bis ( 2,7-bis [N, N-bis (9,9-spiro-bifluoren-2-yl) -amino] -9,9-spirobifluorene; 2,2 '-bis [N, N-] phenylbenzidine; bis (biphenyl-4-yl) -amino] -9,9-spirobifluorenes; 2,2'-bis (N, N-di-phenylamino) -9,9-spirobifluorenes; phthalocyanine-copper complex; 4, 4 ', 4 "-tris (N-3-methylphenyl-N-phenyl-amino) triphenylamine; 4, 4 ', 4" -tris (N- (2-naphthyl) -N-phenyl-amino) triphenylamine; 4.4 ', 4 "-tris (N- (1-naphthyl) -N-phenyl-amino) triphenylamine; 4, 4', 4" -tris (N, N-diphenyl-amino) triphenylamine; titanium oxide phthalocyanine 2, 3, 5, 6-tetrafluoro-7, 7, 8, 8, -tetracyanoquinodimethanes; pyrazino [2,3-f] [1,10] phenanthrolone-2, 3-dicarbonitriles; N, N, N ', N' -Tetrakis (4-methoxyphenyl) benzidines; 2, 7 -Bis [N, N-bis (4-methoxyphenyl) amino] -9,9-spirobifluorenes; 2,2 '-Bis [N, N bis (4-methoxyphenyl) amino] -9, 9-spi robifluorene; 1, 3-bis (carbazol-9-yl) benzene; 1,3,5-tris (carbazol-9-yl) benzene, -4,4 ', 4 "-tris (carbazol-9-yl) triphenylamine; 4,4'-bis (carbazol-9-yl) biphenyl; 4,4'-bis (9-carbazolyl) -2,2'-dimethyl-biphenyl; 2, 7 -Bis (carbazol-9-yl) -9,9-dimentylfluorenes and 2, 2 ', 7, 7'-tetrakis (carbazol-9-yl) -9,9'-spirobifluorenes.

By means of the metal complexes used according to the invention, it is possible to produce semiconducting layers, which if appropriate also have a linear shape, such as, for example, as suffering pathways, contact or the like. Using the organic p-doped materials according to the invention, which can be arranged in electronic organic components, in particular in the form of layers or electrical conduction paths, a multiplicity of electronic components or devices containing them can be produced. For the purposes of the invention, the term "electronic component" also encompasses optoelectronic components.The invention particularly includes organic photodiodes, organic solar cells, organic field-effect transistors and organic photovoltaics in general.

By means of the uses according to the invention, the electronic properties of an electronically functionally effective region of the component, such as its electrical charge carrier mobility, light-absorbing properties or the like, can be advantageously changed. The use according to the invention can be used within a hole conductor or hole transport layer as well as in a bulk heterojunction.

The metal complexes can be used according to the invention in the electronic components but also in layers, conductivity paths, point contacts or the like.

The experimentally found current limitation has not been observed in any of the published material systems suitable for doping. This aspect is particularly important for large-area organic photodiodes because it causes a homogenization of the absorption density. Field peaks on particles or tips in the substrate material are through

Strata with current limitation compensated because the maximum current flow no longer depends on the applied field.

In the following, the invention will be clarified on the basis of some experimental results:

Example for FIG. 5: Analogously to the experiment described above, PDW-2 is by coevaporation in the hole ladder NPB (= bis-N, N, N ', N' - (naphthyl-phenyl) benzidine) doped. For a doping of 0%, 1%, 5% and 10% and 100% PDW2, the characteristics shown in FIG. 5 result.

An additional band in the UV spectrum in the range between 550-600 nm shows the dopability of NPB by PDW-2.

The graph of FIG. 6 shows the photoluminescence spectrum of the layers shown in FIG. 5 in the example described above. Upon excitation of the layer with UV light of 342 nm, the fluorescence of the NPB layer decreases steadily. In line with other dopants, PDW-2 also quenches the fluorescence.

Example for FIG. 7:

On an ITO (indium-tin-oxide = indium-doped tin oxide) electrode successive layers are deposited by thermal evaporation to build an organic light emitting diode (AIq = aluminum trishydroxyquinoline, LiF = lithium fluoride).

a. 50 nm NPB; 40 nm NPB; 40 nm Alq; 0.7 nm LiF; 200 nm Al (circles full) b. 50 nm NPB: PDW-2 [10%]; 40 nm NPB; 40 nm Alq; 0.7 nm LiF; 200 nm Al (circles empty)

By using the doped hole injection layer, the voltage in the IV characteristic is reduced from 5.77 V to 5.03 V in order to achieve a current density of 10 mA / cm ² . The efficiency of this diode is thereby significantly improved, as can be seen from FIG.

By reducing the supply voltage is the

Luminance of 1000 cd / m ² even at 6.18 V with the doping th hole injection layer and only at 7.10 V with the undoped hole injection layer reached (Figure 8).

Example for FIG. 9:

PDW-2 is similarly efficient in structures analogous to the example of Figure 5, as other literature known dopants such as MoO ₃ or F ₄ TCNQ as the comparison shown here proves.

Example for FIG. 10:

The charge carrier density can also be increased in other hole guides such as naph data by the PDW-2 dopant.

Transient dark current measurements show that at a doping level of 10% PDW-2 in Naphdata mobility remains almost constant. As the example of FIG. 10 demonstrates, the charge carrier density available for the organic light-emitting diode increases sharply, which has a very positive effect on the characteristics of organic light-emitting diodes.

(σ = conductivity, μ = mobility, n = number of charge carriers, e = elementary charge)

Example for FIG. 11:

An analogous to Figure 7 constructed light emitting diode with naphdata instead of NPB in the hole injection layer.

a. 50 nm Naphdata; 40 nm NPB; 40 nm Alq; 0.7 nm LiF; 200 nm Al (circles full) b. 50 nm Naphdata: PDW-2 [10%]; 40 nm NPB; 40 nm Alq; 0.7 nm LiF; 200 nm Al (circles empty)

By using the doped hole injection layer, the voltage in the IV characteristic is reduced from 11.6 V to 8.0 V in order to achieve a current density of 10 mA / cm ² . The Efficiency of this diode is thereby significantly improved (FIG. 11)

Example for FIG. 12:

By reducing the supply voltage, the luminance of 1000 cd / m ^{2 is achieved} even at 10.6 V with the doped hole injection layer and only at 13.9 V with the undoped hole injection layer (FIG. 12).

The experimentally found current limitation has not been observed in any of the published material systems suitable for doping. This aspect is particularly important for large-area organic photodiodes because it causes a homogenization of the absorption density. Field peaks on particles or tips in the substrate material are compensated for by current-limiting layers, since the maximum current flow no longer depends on the applied field.

The invention is characterized in particular by the fact that the materials used are compatible with the base materials of organic electronic components and that, for example, in the preferred binuclear metal complexes with the metal-metal bond formally the charge during current transport in the molecule is distributed to two metal atoms, resulting in Stability of the total layer contributes.

The invention relates to the use of a metal complex as p-dopant for an organic semiconducting matrix material, an organic semiconductor material and an organic electronic semiconductor component. The invention discloses the use of metal complexes which act as Lewis acids as p-dopants in organic matrix materials.

Claims

claims

1. Use of a metal complex as p-dopant for doping a hole-conducting organic matrix material, wherein the metal complex is a metal complex with Lewis acid property and acts as an electron pair acceptor.

2. Use according to claim 1, wherein the metal complex is a polynuclear metal complex.

3. Use according to any one of the preceding claims 1 or 2, wherein the central atom of the metal complex is a neutral or charged transition metal atom.

4. Use according to one of the preceding claims, wherein at least one central atom from the 6th to 9th subgroup is selected.

5. Use according to the preceding claim, wherein at least one central atom is rhodium.

Use according to any one of the preceding claims wherein the metal complex is a polynuclear metal complex in which at least one ligand coordinately couples two central atoms.

7. Use according to one of the preceding claims, wherein at least one central atom is square-planar surrounded by ligands.

8. Use according to one of the preceding claims, wherein the metal complex is multi-nuclear and symmetrical.

9. Use according to one of the preceding claims, wherein the ligands are carboxylic acids or carboxylic anions with electron-withdrawing substituents.

Use according to any one of the preceding claims, wherein at least one metal complex has a paddle wheel structure.

11. A semiconductive material prepared using a metal complex according to any one of claims 1 to 10 in the form of an electrically contactable layer.

12. An organic semiconductive material containing at least one organic matrix material and a p-dopant according to any one of claims 1 to 10.

The organic semiconductive material of claim 11, wherein the molar doping ratio of p-dopant to monomeric units of a polymeric matrix molecule is between 1: 1 and 1: 100,000.

14. A process for producing an organic semiconductive material comprising an organic matrix material and a p-dopant, wherein as p-dopant at least one or more metal complexes according to one of claims 1 to 10 are used.

15. An organic electronic component comprising an electronically functionally effective region, wherein the electronically functionally effective region is prepared using at least one or more metal complexes according to any one of claims 1 to 10.

16. The organic electronic device of claim 15, wherein the electronically functionally effective region comprises an organic semiconductive matrix material comprising at least one p-dopant for altering the electronic properties of the semiconductive matrix material using at least one or more metal complexes according to any one of claims 1 to 10 is doped.

17. Organic electronic component according to one of claims 15 to 16 in the form of a photovoltaic cell, an organic solar cell, an organic diode, an organic photodiode and / or an organic field effect A transistor in which the semiconductive material doped with at least one or more metal complexes according to any one of claims 1 to 10 constitutes an electronically functionally effective part of the electronic component.